XI. LITERATURE AND HISTORY (part 4 of 5)

XI. LITERATURE AND HISTORY (part 4 of 5)

A similar dome-building or a composition of the polythalamous shell by pairs of cupolas we find also in the next (fifth) family, the Zonarida. But here the true cause of the peculiar dome-structure is quite different, not an apposition of new chambers, but the constriction of a cortical shell-like Larnacalpis by two or more constrictions. These constrictions lie in dimensive planes (or in planes parallel to these), and therefore the cupolas are (all or partly) in diagonal planes, a condition quite opposite to that found in the Tholonida. One of the annular constrictions is constantly in the sagittal plane (separating the right and left halves of the shell). The number of the constrictions in the few genera is two, three, and four, and therefore the number of the cupolas four, six, or eight. As this cortical shell constantly encloses a trizonal medullary shell (or Larnacilla-shell), we cannot doubt that the Zonarida must be derived from the Larnacida.

{603}Whilst in all the foregoing five families of #Larcoidea# the shell-form is regular and their geometrical fundamental form is a lentellipsis (or a triaxial ellipsoid, with three unequal isopolar dimensive axes), in the four remaining families of this suborder the shell becomes bilateral or irregular (with the poles of the axes unequal). In two of these families (Lithelida and Streblemida) the growth of the shell becomes spiral, in the last two families (Soreumida and Phorticida) quite irregular. But as in all four families we encounter the typical trizonal medullary shell (or Larnacilla-shell), we are convinced that they must be derived (wholly or partially) from the Larnacida.

The Lithelida (the sixth family) are #Larcoidea# with spiral growth and bilateral form (like Nautilus); therefore the spiral line lies in one plane and this spiral plane divides the whole shell into two symmetrical halves (right and left). The axis of the spiral (around which the shell winds) is a straight line, one of the three dimensive axes. In the greater part of Lithelida (in the Larcospirida) the primordial of central chamber of the polythalamous shell is a trizonal medullary shell or Larnacilla-shell, and the growth of the first spiral turning begins as the development of the first (transverse) cortical girdle of Amphipyle; but as one wing (or lateral half) of this girdle grows more rapidly than the other, it overgrows the latter and begins the spiral winding; if the other wing follow and overgrow the first, the spiral becomes double. Each of the three dimensive girdles (of the Pylonida) may begin the spiral winding. There can be no doubt that all these Lithelida (the Larcospirida) must be derived from the Pylonida, by unequal growth of the two halves of one girdle. Perhaps from these may also derived the other part of this family, the Spiremida (Spirema and Lithelius); in these the primordial chamber of the spiral shell is simple, and may be derived by reduction of the original Larnacilla-shell. But it is also possible that the Spiremida proceed directly from the Larcarida, and that their ancestors did not possess a Larnacilla-shell.

The Streblemida (the seventh family) are #Larcoidea# with spiral growth and asymmetrical form of the polythalamous shell (like Helix or Turrilites); therefore the spiral line is twisted like a winding stair, and the spiral face is curved and divides the shell into two unequal halves. The Streblemida have the same likeness and relation to the turbinoid Foraminifera (Rotalia, Globigerina, &c.) as the Lithelida to the nautiloid Foraminifera (Polystomella, Nummulina, &c.). As in these calcareous Rhizopods also the peculiar growth of the siliceous Streblemida begins from a primordial chamber to which a variable number of roundish chambers (of increasing size) is apposed. But the building of these chambers and of their septa is by no means so regular and complete as in the greater number of turbinoid Foraminifera. As in a part of this family the primordial chamber is Larnacilla-shell, these also may be derived from the Larnacida, but the other part (with simple central chamber) is perhaps produced directly from the Larcarida.

The eighth family, Soreumida, is perhaps derived from the Streblemida by the loss of the spiral growth. The polythalamous shell is similar to the latter, but the chambers are {604}aggregated without any order, like the Acervulinida among the Foraminifera. In some cases also here the primordial chamber is a trizonal Larnacilla-shell, in other cases it is a simple, subspherical or lentelliptical shell.

The last family, the Phorticida, is formed of irregular #Larcoidea#, in which a lentelliptical trizonal Larnacilla-shell (as an inner medullary shell) is enveloped by an irregular, latticed, or spongy cortical shell. They can be regarded as abnormalities or irregular deformities of Larnacida or Pylonida.

The central capsule of the #Larcoidea# is originally lentelliptical and preserves this form, the "triaxial ellipsoid," in the greater number of genera. In some groups it follows the prevalent growth of the shell in the direction of one of the three dimensive axes, and becomes prolonged in this way. In many chambered forms (particularly Tholonida and Zonarida) the growing central capsule gets constricted, corresponding to the constrictions of the shell. In the Soreumida and Phorticida its form often becomes irregular. But in general for the greater number of #Larcoidea# the lentelliptical form of their central capsule is quite characteristic.

Synopsis of the Families of #Larcoidea#.

------------------------------------------------------------------------- #Larcoidea# with a regular or symmetrical shell, the growth of which is determined by the three dimensive axes. (Both poles of each axis are equal.) ------------------------------------------------------------------------- {Medullary shell absent or Cortical shell completely { simple (spherical or latticed, without external { lentelliptical), 1. LARCARIDA. gates (or interzonal { fissures), without annular {Medullary shell trizonal or constrictions and domes. { Larnacilla-shaped { (composed of three { dimensive girdles), 2. LARNACIDA.

Cortical shell incompletely latticed, with two to four or more symmetrically disposed gates or fissures remaining between latticed dimensive girdles, 3. PYLONIDA.

Cortical shell completely }Constrictions of the latticed, without external } cortical shell in gates (or interzonal } diagonal planes; domes fissures), with two or } in dimensive axes, 4. THOLONIDA. more annular constrictions,} which separate three to }Constrictions of the six or more dome-shaped } cortical shell in protuberances. } dimensive planes; domes } in diagonal axes, 5. ZONARIDA. ------------------------------------------------------------------------- #Larcoidea# with a symmetrical or irregular shell, either with spiral growth or with quite irregular growth. (Both poles of one axis are different.) ------------------------------------------------------------------------- {Spiral cortical shell bilateral { (with plane spiral), 6. LITHELIDA. Cortical shell with { spiral growth. {Spiral cortical shell { asymmetrical (with ascending { spiral), 7. STREBLEMIDA.

{Cortical shell simple, with { one single chamber, 8. PHORTICIDA. Cortical shell with quite { irregular growth. {Cortical shell composed of { a number of heaped up { or aggregated chambers, 9. SOREUMIDA.

{605}Family XXIV. #LARCARIDA#, Haeckel, 1883 (Pl. 50, figs. 1, 2).

Definition.--#Larcoidea# with a regular, completely latticed, lentelliptical cortical shell, without open gates and annular constrictions; medullary shell absent or simple (not trizonal), connected with the cortical shell by radial beams.

The family #Larcarida# opens the long series of #Larcoidea# as the most simple group of this suborder. It commences with Cenolarcus, a quite simple lentelliptical latticed shell, which is characterised by three unequal isopolar dimensive axes, perpendicular one to another. The major of these three axes is the longitudinal or principal, the middle is the lateral or transverse, and the minor is the equatorial or sagittal axis (as in the human body). Among the three dimensive planes, which are determined by pairs of these axes, the lateral plane is the largest (halved by the crossed principal and lateral axes). The intermediate is the sagittal plane or median plane (halved by the crossed principal and sagittal axes). The smallest is the equatorial plane or transverse plane (halved by the crossed lateral and sagittal axes). Therefore the shell has all the characters of the true Lentellipsis or of the "triaxial ellipsoid," and its axes agree with the three axes of the "rhombic crystalline system."

In the three subfamilies of Larcarida this lentelliptical shell assumes a different shape: in the Cenolarcida it remains simple, in the Spongolarcida it becomes spongy (sometimes quite filled out with a spongy framework), in the Coccolarcida it is composed of two or more concentric lentelliptical shells (at least an inner medullary and one outer cortical shell). These shells are simply connected by radial beams, and not, as in the Larnacida, by latticed wings (or half girdles).

The network of the Larcarida shell is sometimes regular, commonly irregular (as in the greater number of #Larcoidea#). The surface of the shell is sometimes smooth or thorny, at other times covered with radial spines. These are often symmetrically disposed, either on the poles of the dimensive axes or in crossed diagonal planes.

The central capsule is a true "lentellipsis" in a geometrical sense; it is halved by three elliptical dimensive planes of different sizes, perpendicular one to another. In the Cenolarcida the central capsule lies freely inside the simple (cortical) shell, only separated from it by the jelly-mantle. In the Coccolarcida it contains the medullary shell, and is enclosed by the simple or double cortical shell, perforated by the radial beams connecting the two shells. The spongy shell of the Spongolarcida exhibits a different relation to the central capsule: in Spongolarcus the latter lies freely in the internal cavity of the spongy shell; in Stypolarcus, where this cavity is quite filled with a spongy network, the central capsule also contains a part of it.

The morphological and phylogenetic relations of the Larcarida to the other families of SPUMELLARIA admit of a different explanation. As this family contains the {606}most simple forms of all #Larcoidea#, we can regard the Cenolarcus as the common ancestral form of this group, having originated from Actilarcus (or the lentelliptical Actissa) by the building of a simple lentelliptical lattice-shell. But it is also possible that a part of the Larcarida (or all?) descend from Larnacida by reduction or loss of the original Larnacilla-shell (compare Cenolarcus triaxonius, p. 607).

Synopsis of the Genera of the Larcarida.

------------------------------------------------------------------------- I. Subfamily Cenolarcida. Shell simple, latticed (lentelliptical cortical shell). ------------------------------------------------------------------------- Without radial spines, 266. Cenolarcus.

With radial spines, 267. Larcarium. ------------------------------------------------------------------------- II. Subfamily Coccolarcida. Shell composed of two or more concentric latticed shells (inner medullary and outer cortical). ------------------------------------------------------------------------- Without radial spines, 268. Coccolarcus.

With radial spines, 269. Larcidium. ------------------------------------------------------------------------- III. Subfamily Spongolarcida. Shell spongy, partly or whole composed of a spongy framework. ------------------------------------------------------------------------- With an internal cavity, 270. Spongolarcus.

Without an internal cavity, 271. Stypolarcus.

Subfamily 1. CENOLARCIDA, Haeckel.

Definition.--#Larcarida# with a simple, lentelliptical latticed shell (cortical shell without a medullary shell).

Genus 266. Cenolarcus,[305] n. gen.

Definition.--#Larcarida# with a simple, lentelliptical latticed shell, without a medullary shell, without radial spines.

The genus Cenolarcus begins the group of #Larcoidea# as the most simple form of this suborder. It corresponds to Cenosphæra among the #Sphæroidea#, to Cenodiscus among the #Discoidea#, to Cenellipsis among the #Prunoidea#. The simple latticed shell is distinguished from that of the three other genera by its typical lentelliptical form, a triaxial ellipsoid with three dimensive axes of unequal length. Probably Cenolarcus is the original ancestral form of the #Larcoidea#, derived from Actilarcus (the lentelliptical Actissa) by the formation of a simple fenestrated shell around the lentelliptical central capsule. But possibly also some species of Cenolarcus may be derived from Coccolarcus or Larnacilla by reduction and loss of the medullary shell (compare Cenolarcus triaxonius, n. sp.).

{607}1. Cenolarcus primordialis, n. sp. (Pl. 50, figs. 7, 7_a_, 7_b_).

Network of the shell regular, with circular, hexagonally framed pores, twice as broad as the elevated bars; about ten pores on the half meridian, eight on the half equator. Surface a little rough. Proportion of the three dimensive axes = 2 : 2.5 : 3.

Dimensions.--Principal axis (or length) 0.12, transverse axis (or breadth) 0.1, sagittal axis (or thickness) 0.08; pores 0.01, bars 0.005.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

2. Cenolarcus dimensivus, n. sp.

Network of the shell regular, with circular pores (without hexagonal frames), three times as broad as the thin bars; about twelve pores on the half meridian, nine on the half equator. Surface thorny. Proportion of the three dimensive axes = 3 : 4 : 5.

Dimensions.--Principal axis 0.15, transverse axis 0.12, sagittal axis 0.09; pores 0.012, bars 0.004.

Habitat.--North Pacific, Station 244, surface.

3. Cenolarcus triaxonius, n. sp.

Network of the shell regular, with circular, hexagonally framed pores, four times as broad as the thin bars; about twelve pores on the half meridian, nine on the equator. Surface smooth. From the inner surface of the shell arise six very thin radial beams, opposite in pairs in the three dimensive axes; all six beams end freely in a little knob, at an equal distance from the centre; therefore this remarkable species seems to have lost a medullary shell (descending from Coccolarcus or Larnacilla?). Proportion of the three dimensive axes = 2 : 2.5 : 3.

Dimensions.--Principal axis 0.13, transverse axis 0.11, sagittal axis 0.09; pores 0.012, bars 0.03.

Habitat.--Tropical Atlantic, Station 338, depth 1990 fathoms.

4. Cenolarcus lentellipticus, n. sp.

Network of the shell regular, with circular pores of the same breadth as the thick bars; about eighteen pores on the half meridian, fourteen on the half equator. Surface smooth. Proportion of the three dimensive axes = 2 : 3 : 4.

Dimensions.--Principal axis 0.16, transverse axis 0.12, sagittal axis 0.08; pores and bars 0.004.

Habitat.--Western Tropical Pacific, Station 224, surface.

5. Cenolarcus minimus, n. sp.

Network of the shell subregular, with very small circular pores of the same breadth as the bars; only four pores on the half meridian, three on the half equator. Surface smooth. Proportion of the three dimensive axes = 3 : 4 : 5.

{608}Dimensions.--Principal axis 0.05, transverse 0.04, sagittal axis 0.03; pores and bars 0.006.

Habitat.--Pacific, central area, Station 266, depth 2750 fathoms.

Genus 267. Larcarium,[306] n. gen.

Definition.--#Larcarida# with a simple, lentelliptical latticed shell, without a medullary shell; surface covered with radial spines.

The genus Larcarium differs from Cenolarcus only in the possession of radial spines on the surface of the simple fenestrated lentelliptical shell. These spines are commonly disposed symmetrically, opposite in pairs, either on the poles of the three dimensive axes, or on the poles of certain diagonal axes. Larcarium differs from the similar genera Larcidium, Larnacidium, and Larnacantha by the absence of any medullary shell.

1. Larcarium amphistylum, n. sp.

Shell thorny, with two large conical spines, opposite on both poles of the principal axis, somewhat longer than it. Network of the shell regular, with circular, hexagonally framed pores, twice as broad as the bars; about twelve pores on the half meridian, ten on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5.

Dimensions.--Principal axis (or length) 0.15, transverse axis (or breadth) 0.12, sagittal axis (or thickness) 0.09; pores 0.01, bars 0.005.

Habitat.--Pacific, central area, Station 274, depth 2750 fathoms.

2. Larcarium staurostylum, n. sp.

Shell smooth, with four short three-sided pyramidal spines of equal length, opposite in pairs on the poles of the principal and lateral axes. Network of the shell regular, with circular pores of the same breadth as the bars; about eight pores on the half meridian, six on the half equator. Proportion of the three dimensive axes = 2 : 2.5 : 3.

Dimensions.--Length of the shell 0.12, breadth 0.1, thickness 0.08; pores and bars 0.006.

Habitat.--South Pacific, Station 300, depth 1375 fathoms.

3. Larcarium hexastylum, n. sp.

Shell smooth, with six short conical spines of equal length (= the shortest axis of the shell), opposite in pairs on the poles of the three dimensive axes. Network of the shell subregular, with {609}circular pores three times as broad as the bars; about eleven pores on the half meridian, nine on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5.

Dimensions.--Length of the shell 0.1, breadth 0.08, thickness 0.06, pores 0.006; bars 0.002.

Habitat.--North Pacific, Station 244, surface.

4. Larcarium axostylum, n. sp.

Shell thorny, with six strong conical radial spines, opposite in pairs on the poles of the three dimensive axes. All three pairs are of different sizes, the length of each spine corresponding nearly to the size of the shell-axis, of which it is the prolongation. Network of the shell subregular, with circular pores twice as broad as the bars; ten on the half meridian, eight on the half equator. Proportion of the three dimensive axes = 2 : 3 : 4.

Dimensions.--Length of the shell 0.12, breadth 0.09, thickness 0.06; pores 0.01, bars 0.005.

Habitat.--Western Tropical Pacific, Station 225, depth 4475 fathoms.

5. Larcarium octostylum, n. sp.

Shell thorny, with eight thin cylindrical radial spines, opposite in pairs in two crossed diagonal planes. Network of the shell irregular, with roundish pores, twice to four times as broad as the bars; nine to eleven on the half meridian, five to seven on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5.

Dimensions.--Length of the shell 0.11, breadth 0.09, thickness 0.07; pores 0.006 to 0.012, bars 0.003.

Habitat.--Pacific, central area, Station 267, surface.

6. Larcarium polystylum, n. sp.

Shell thorny, with numerous (twenty to thirty) stronger conical radial spines, about as long as the shortest axis of the shell. Network of the shell irregular, with roundish pores, twice to four times as broad as the bars; seven to eight on the half meridian, five to six on the half equator. Proportion of the three dimensive axes = 1 : 2 : 3.

Dimensions.--Length of the shell 0.09, breadth 0.06, thickness 0.03; pores 0.006 to 0.012, bars 0.003.

Habitat.--South Atlantic, Station 323, surface.

7. Larcarium chætostylum, n. sp.

Shell bristly, with very numerous (sixty to eighty or more) very thin, bristle-like, radial spines, somewhat longer than the longest axis of the shell. Network irregular, with very small roundish pores, about the same size as the bars; sixteen to eighteen on the half meridian, thirteen to fifteen on the half equator. Proportion of the three dimensive axes = 1 : 1.5 : 2.

{610}Dimensions.--Length of the shell (without spines) 0.13, breadth 0.1, thickness 0.07; pores and bars 0.004 to 0.006.

Habitat.--Pacific, central area, Station 273, surface.

Subfamily 2. COCCOLARCIDA, Haeckel.

Definition.--#Larcarida# with encased lentelliptical shell, composed of two or more concentric lentelliptical latticed shells, which are united by radial beams (at least one inner medullary shell and one outer cortical shell).

Genus 268. Coccolarcus,[307] n. gen.

Definition.--#Larcarida# with two concentric latticed shells, an outer lentelliptical cortical shell, and an inner (spherical or lentelliptical) medullary shell, both connected by radial beams. Surface without radial spines.

The genus Coccolarcus differs from Cenolarcus by the possession of an internal medullary shell. This is quite simple, either spherical or lentelliptical, and connected with the outer cortical shell by a number of radial beams. In the similar Larnacilla this connection is effected by four internal latticed lamellæ (the half lateral wings of the transverse girdle); therefore we find here four internal gates (on the poles of the principal axis), absent in Coccolarcus.

1. Coccolarcus lentellipsis, n. sp.

Cortical shell with smooth surface and regular network; pores circular, twice as broad as the bars; about thirteen on the half meridian, eleven on the half equator. Proportion of the three dimensive axes = 3 : 4 : 5. Medullary shell spherical, half as broad as the transverse radius.

Dimensions.--Principal axis (or length) of the cortical shell 0.15, transverse axis (or breadth) 0.12, sagittal axis (or thickness) 0.09; pores 0.01, bars 0.005; diameter of the medullary shell 0.03.

Habitat.--Pacific, central area, Station 272, depth 2600 fathoms.

2. Coccolarcus platellipsis, n. sp.

Cortical shell with thorny surface and irregular network; pores roundish, twice to three times as broad as the bars; sixteen to eighteen on the half meridian, ten to twelve on the half equator. Proportion of the three dimensive axes = 1 : 2 : 3. Medullary shell lentelliptical, one-third as large as the cortical shell.

{611}Dimensions.--Length of the cortical shell 0.17, breadth 0.11, thickness 0.06; pores 0.008 to 0.012, bars 0.004; medullary shell 0.03 to 0.06.

Habitat.--Pacific, central area, Station 274, depth 2750 fathoms.

Genus 269. Larcidium,[308] n. gen.

Definition.--#Larcarida# with two concentric latticed shells, an outer lentelliptical cortical shell, and an inner (spherical or lentelliptical) medullary shell, both connected by radial beams. Surface covered with radial spines.

The genus Larcidium differs from the foregoing Coccolarcus only in the possession of radial spines, and bears to it the same relation that Larcarium does to Cenolarcus. The spines are commonly symmetrically disposed, opposite in pairs in the dimensive axes, sometimes also in diagonal axes.

1. Larcidium dissacanthum, n. sp.

Cortical shell with thorny surface and regular network; pores circular, hexagonally framed, three times as broad as the bars; about thirteen on the half meridian, eleven on the half equator. Proportion of the three dimensive axes = 2 : 3 : 5. Medullary shell spherical, one-fourth as broad as the cortical, connected with it by two thin beams, lying in the principal axis, and prolonged on its poles into two strong conical spines, somewhat longer than the greatest axis.

Dimensions.--Length of the cortical shell (or principal axis) 0.15, breadth 0.09, thickness 0.07; pores 0.015, bars 0.005; medullary shell 0.025.

Habitat.--North Pacific, Station 253, depth 3125 fathoms.

2. Larcidium hexacanthum, n. sp.

Cortical shell with smooth surface and regular network; pores circular, twice as broad as the bars; about eleven on the half meridian, nine on the half equator. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell spherical, one-third as broad as the cortical. On the surface six strong, three-sided pyramidal spines, all about as long as the breadth of the cortical shell.

Dimensions.--Length of the cortical shell 0.12, breadth 0.1, thickness 0.08; pores 0.01, bars 0.005; medullary shell 0.035.

Habitat.--Pacific, central area. Station 266, surface.

3. Larcidium axacanthum, n. sp.

Cortical shell with rough surface and irregular network; pores roundish, twice to four times as broad as the bars; about fifteen to nineteen on the half meridian, twelve to fourteen on the half {612}equator. Proportion of the three axes = 2 : 3 : 4. Medullary shell lentelliptical, of the same form and structure as the cortical, but only one-third as large, connected with it by six thin radial beams, lying in pairs in the three dimensive axes; on the outside they are prolonged into six strong conical radial spines, which are in pairs of different size (as in Larcarium axostylum); the length of each spine nearly equals the axis of the cortical shell, of which it is the prolongation.

Dimensions.--Length of the cortical shell (and the principal spines) 0.18, breadth of it (and length of the lateral spines) 0.135, thickness of it (and length of the sagittal spines) 0.09; pores 0.005 to 0.013, bars 0.003.

Habitat.--Pacific, central area, Station 271, surface.

4. Larcidium octacanthum, n. sp.

Cortical shell thorny, with irregular network; pores roundish, once to four times as broad as the bars; about thirteen to fifteen on the half meridian, eleven to thirteen on the half equator. Proportion of the three axes = 1 : 2.5 : 4. Medullary shell lentelliptical, one-fifth as large as the cortical, connected with it by eight radial beams, which are situated in two crossed diagonal planes (opposite in pairs), and are prolonged on the surface into eight long and thin cylindrical radial spines similar to Tetrapyle octacantha.

Dimensions.--Length of the cortical shell 0.16, breadth 0.11, thickness 0.045; pores 0.003 to 0.012, bars 0.003; medullary shell 0.02 to 0.03.

Habitat.--Pacific, central area, Station 263, depth 2650 fathoms.

5. Larcidium dodecanthum, n. sp. (Pl. 50, figs. 8, 8_a_).

Cortical shell rough, with irregular network; pores roundish, twice to four times as broad as the bars; about twelve to fourteen on the half meridian, eight to ten on the half equator. Proportion of the three axes = 2 : 3 : 4. Medullary shell lentelliptical, one-third as large as the cortical, connected with it by twelve thin radial beams, which are prolonged outside into twelve strong conical radial spines, about half as long as the breadth of the shell.

Dimensions.--Length of the cortical shell 0.14, breadth 0.1, thickness 0.07; pores 0.008 to 0.015, bars 0.004; medullary shell 0.04 to 0.05.

Habitat.--South Pacific, Station 288, surface.

6. Larcidium polyacanthum, n. sp.

Cortical shell spiny, with irregular network; pores roundish, once to twice as broad as the bars; about ten to twelve on the half meridian, six to eight on the half equator. Proportion of the three axes = 1 : 2 : 3. Medullary shell lentelliptical, half as large as the cortical shell, connected with it by numerous (twenty to twenty-five) radial beams, which are prolonged outside into three-sided pyramidal spines, about as long as the breadth of the shell.

Dimensions.--Length of the cortical shell 0.18, breadth 0.12, thickness 0.06; pores 0.01 to 0.015, bars 0.008; medullary shell 0.03 to 0.09.

Habitat.--North Pacific, Station 244, depth 2900 fathoms.

{613}Subfamily 3. SPONGOLARCIDA, Haeckel.

Definition.--#Larcarida# with spongy lentelliptical shell (with or without enclosed medullary shell).

Genus 270. Spongolarcus,[309] n. gen.

Definition.--#Larcarida# with lentelliptical spongy shell, containing a central cavity of the same form, without medullary shell (without radial spines).

The genus Spongolarcus differs from Cenolarcus (its probable ancestral form) only in the development of spongy framework forming the wall of the hollow lentelliptical shell. It corresponds, therefore, to Plegmosphæra among the #Sphæroidea#, and to Spongellipsis among the #Prunoidea#. From these two similar spongy #Sphærellaria# it differs in its characteristic lentelliptical form, with three dimensive axes of unequal length.

1. Spongolarcus lentellipsis, n. sp.

Spongy network of the shell very loose, its meshes fifteen to twenty times as broad as the bars. Surface of the shell nearly smooth; diameter of its internal cavity twice as large as the thickness of its wall. Proportion of the three dimensive axes = 2 : 3 : 4.

Dimensions.--Length 0.16, breadth 0.12, height 0.08; thickness of the spongy wall 0.05.

Habitat.--Pacific, central area, Station 274, surface.

2. Spongolarcus triaxonius, n. sp.

Spongy network of the shell rather loose, its meshes twelve to sixteen times as broad as the bars. Surface of the shell rough; diameter of its internal cavity about eight times as large as the thickness of its wall. Proportion of the three dimensive axes = 2 : 2.5 : 3.

Dimensions.--Length 0.25, breadth 0.2, height 0.16; thickness of the spongy wall 0.025.

Habitat.--North Pacific, Station 253, surface.

3. Spongolarcus dimensivus, n. sp.

Spongy network of the shell dense, its meshes four to eight times as broad as the bars. Surface of the shell thorny; diameter of its internal cavity about fifteen times as large as the thickness of its wall. Proportion of the three dimensive axes = 3 : 4 : 5.

Dimensions.--Length 0.2, breadth 0.16, height 0.12; thickness of the spongy wall 0.01.

Habitat.--Western Tropical Pacific, Station 225, depth 4475 fathoms.

{614}4. Spongolarcus amphicentria, Haeckel.

? Amphicentria salpa, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 296; Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, Taf. ii. fig. 18.

? Spongurus salpa, Haeckel, 1862, Monogr. d. Radiol., p. 466.

Spongy network of the shell compact, its meshes about the same breadth as the bars. Surface of the shell spiny, with some larger spines around the poles of the axis; diameter of the internal cavity about six times as large as the thickness of its wall. Proportion of the three dimensive axes = 1 : 2 : 3. (Perhaps this Spongolarcus is identical with Amphicentria salpa, very imperfectly described and figured by Ehrenberg, loc. cit.?)

Dimensions.--Length 0.14, breadth 0.09, height 0.05; thickness of the spongy wall 0.015.

Habitat.--North Atlantic; off Greenland, 1000 fathoms, Ehrenberg; Station 64, depth (2700) fathoms.

Genus 271. Stypolarcus,[310] n. gen.

Definition.--#Larcarida# with lentelliptical spongy shell, composed of compact spongy framework, without central cavity and medullary shell (without radial spines).

The genus Stypolarcus differs from Spongolarcus in the absence of any central cavity. This is quite filled up by spongy framework, which forms the whole mass of the lentelliptical body. Stypolarcus bears therefore the same relation to Spongolarcus that Styptosphæra does to Plegmosphæra.

1. Stypolarcus spongiosus, n. sp.

Lentelliptical shell composed in the whole mass of loose, spongy framework of similar texture, with irregular meshes, about ten to twenty times as broad as the thin bars. Surface rough, without radial spines. Proportion of the three axes = 3 : 4 : 5.

Dimensions.--Length 0.2, breadth 0.16, height 0.12.

Habitat.--Antarctic Ocean, Station 157, depth 1950 fathoms.

Family XXV. #LARNACIDA#, Haeckel, 1883 (Pl. 50, figs. 3-8).

Definition.--#Larcoidea# with a regular, completely latticed, lentelliptical cortical shell, without open gates and annular constrictions; either this cortical shell or the enclosed medullary shell is trizonal, composed of three elliptical, latticed, dimensive girdles of different sizes, perpendicular one to another.

{615}The family #Larnacida# immediately follows the Larcarida as the next simple group of all #Larcoidea#; some genera of both groups (such as Larnacalpis and Coccolarcus, or Larnacantha and Larcidium) may easily be confounded from their being so much alike. In both the lentelliptical shell is composed of two concentric shells, an inner (medullary) and an outer (cortical) shell. But the connection between these shells and the construction of the inner shell is quite different in the two groups. Whilst in the Larcarida the medullary shell is connected with the cortical shell simply by radial beams, here in the Larnacida this connection is effected by two latticed lamellæ, which are the lateral wings of a transverse girdle. Therefore we encounter here for the first time that peculiar mode of growth which characterises the greater part of the #Larcoidea#, but particularly the Pylonida. But whilst in the Pylonida between the three crossed lattice-girdles, remain four open gates, here in the Larnacida the gates become closed by lattice-work; the lentelliptical cortical shell becomes perfect.

The most simple genus of Larnacida, and no doubt the common ancestral form of this whole family, is Larnacilla (Pl. 50, figs. 1, 1_a_, 1_b_). The most important shell of this typical genus is composed of a simple lentelliptical medullary shell and of three elliptical latticed girdles surrounding it, perpendicular one to another. These three "dimensive girdles" lie in the perimeter of the three dimensive planes, the minor (and first) in the equatorial plane, the second (and major) in the lateral plane, the third (and intermediate) in the sagittal plane. Therefore we have before us the same "trizonal shell" as in the important genus Trizonium among the Pylonida. But whilst in Trizonium, as in all Pylonida, the four gates between the girdles remain open, here in Larnacilla they become perfectly closed by lattice-work.

The formation of the typical "Larnacilla-shell" begins with a simple, spherical or lentelliptical lattice-shell, from both sides of which arise two latticed "lateral wings" opposite on the poles of the transverse axis. These two wings are comparable to the lateral chambers of Tholartus (among the Tholonida), but differ by two large openings. Each wing is a short cylindrical tube with latticed wall, open at both ends; the axis of the tube (going through the centre of the open ends) is parallel to the principal axis of the whole shell (and of the central chamber). Therefore both wings form together a transverse ring, the middle of which encloses the central chamber. The distal parts of both wings grow towards the poles of the principal axis; if they became united here, the second (lateral) girdle would be complete. Between it and the first girdle four open gates remain ("Tetrapyle"); but these become overgrown by the third or sagittal girdle, and at last the gates between this and the two other girdles become closed by lattice-work. This perfect fenestration of the trizonal cortical shell, and the complete closing of the gates between the girdles by network, is the only difference between Trizonium and Larnacilla.

In Larnacilla and in the nearly allied Larnacidium (only differing by radial spines {616}on the surface) the "trizonal shell" is an external or "cortical shell," enclosing the central capsule, the interior of which only contains the simple central chamber and the jointed proximal parts of both lateral wings. In the other genera of Larnacida (by proceeding growth) this trizonal Larnacilla-shell becomes enclosed by the growing central capsule and is now only a "medullary shell," whilst on the outside of the central capsule in the same manner is developed an outer cortical shell (Larnacalpis, Larnacantha); and perhaps the same process may be repeated. But sometimes also this cortical shell becomes doubled by a simple envelop of network (Larnacoma). In the Larnacospongida the cortical shell is composed of a spongy framework (corresponding to the Spongolarcida in the foregoing family).

The lattice-work of the Larnacida is commonly irregular (as in most other #Larcoidea#), and its pores have little signification for the different species. On the outer surface often arise radial spines, symmetrically disposed either in dimensive planes or in diagonal planes.

The central capsule is constantly a true lentellipsis or a "triaxial ellipsoid," characterised by three halving, elliptical dimensive planes, perpendicular one to another. It bears a different relation to the skeleton in the two subfamilies of Larnacida. In the first subfamily, the Larnacillida (Larnacilla, Larnacidium), the central capsule encloses only the simple spherical or lentelliptical central chamber ("simple medullary shell"), and is enveloped by the trizonal cortical shell. In the other subfamily, the Larnacalpida (Larnacalpis, Larnacospongus, &c.), this trizonal "Larnacilla-shell" becomes enclosed by the overgrowing central capsule, which now becomes enveloped by an external, latticed or spongy, lentelliptical "cortical shell."

Synopsis of the Genera of Larnacida.

------------------------------------------------------------------------- I. Subfamily Larnacillida. Medullary shell simple, spherical or subspherical. Cortical shell lentelliptical, trizonal; between them four gates. ------------------------------------------------------------------------- Shell without radial spines, 272. Larnacilla.

Shell with radial spines, 273. Larnacidium. ------------------------------------------------------------------------- II. Subfamily Larnacalpida. Medullary shell Larnacilla-shaped, double; the inner spherical or subspherical, the outer lentelliptical and trizonal. ------------------------------------------------------------------------- { { Without radial { Cortical { spines, 274. Larnacalpis. { shell { Cortical shell simple { simple. { With radial or double, but not { { spines, 275. Larnacantha. spongy. { { Cortical shell double, { without radial spines, 276. Larnacoma.

{ Shell without radial Cortical shell simple { spines, 277. Larnacospongus. or double, wholly or { partly spongy. { Shell with radial spines, 278. Larnacostupa.

{617}Subfamily 1. LARNACILLIDA, Haeckel.

Definition.--#Larnacida# with a simple, spherical or lentelliptical, medullary shell, connected by the lateral wings of a latticed transverse girdle with the simple lentelliptical trizonal cortical shell; the central capsule encloses the former and is enveloped by the latter.

Genus 272. Larnacilla,[311] n. gen.

Definition.--#Larnacida# with a simple lentelliptical cortical shell, connected by the lateral wings of a latticed transverse girdle with the simple, spherical or lentelliptical, medullary shell. Surface without radial spines.

The genus Larnacilla represents the most simple form of Larnacida, and at the same time the most important common ancestral form, from which the greater number of #Larcoidea# may be derived, viz., all those genera which possess the characteristic "Larnacilla-shaped medullary shell." This typical form of medullary shell may be derived from the genus Trizonium among the Pylonida by the closing of the four open gates of this genus. The free opening of these four gates becomes overgrown and closed by lattice-work, developed from the free edges of the three crossed girdles, and thus finally all three girdles are united in the form of a simple lentelliptical shell (Pl. 50, figs. 1, 1_a_, 1_b_). Seen from the sagittal poles (or from the poles of the shortest axis, fig. 1), the shell exhibits on both sides of the small spherical medullary shell the two lateral wings of the transverse girdle from the face; seen from the lateral poles (or from the poles of the transverse axis, fig. 1_a_), one of these wings appears in the optical section as an oblong ring, which seemingly encloses the concentric medullary shell, and on both sides is grown together with the sagittal girdle; seen from the principal poles (or from the poles of the longitudinal axis, fig. 1_b_), both wings exhibit their elliptical opening (at the right and left from the central medullary shell). The two concentric shells are only connected by the two lateral tube-like wings of the transverse girdle; the lateral and the sagittal girdles have no connection with the medullary shell. The latter is sometimes spherical, at other times lentelliptical.

1. Larnacilla typus, n. sp. (Pl. 50, fig. 1, 1_a_, 1_b_).

Cortical shell with smooth surface and with subregular network; pores twice as broad as the bars; about twelve pores on the half meridian, ten on the half equator. Proportion of the three dimensive axes = 2 : 3 : 4. Internal four gates (between transverse and lateral girdles) roundish-triangular, little broader than high. Medullary shell spherical, scarcely one-third as broad as the lentelliptical cortical shell.

{618}Dimensions.--Length of the cortical shell (or principal axis) 0.13, breadth of it (or transverse axis) 0.1, height of it (or sagittal axis) 0.07; pores 0.006, bars 0.003; medullary shell (diameter) 0.03.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

2. Larnacilla prometor, n. sp.

Cortical shell with rough surface and regular network; pores three times as broad as the bars; about ten on the half meridian, eight on the half equator. Proportion of the three axes = 1 : 2 : 3. Internal four gates (between transverse and lateral girdles) kidney-shaped, twice as broad as high. Medullary shell lentelliptical, of the same form as the external cortical shell, but only one third as large.

Dimensions.--Length of the cortical shell 0.15, breadth 0.1, height 0.05, pores 0.015, bars 0.005; medullary shell 0.02 to 0.05.

Habitat.--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

3. Larnacilla subglobosa, n. sp.

Cortical shell nearly spherical, with thorny surface and irregular network; pores roundish, twice to four times as broad as the bars; twelve to sixteen in the half circumference. Proportion of the three axes very little different = 1.3 : 1.4 : 1.5. Internal four gates elliptical, one and a half times as broad as high. Medullary shell spherical, one-fourth as broad as the cortical shell.

Dimensions.--Length of the cortical shell 0.15, breadth 0.14, height 0.13; pores 0.006 to 0.012, bars 0.003; medullary shell 0.035.

Habitat.--Pacific, central area. Station 266, depth 2750 fathoms.

4. Larnacilla medullaris, n. sp.

Cortical shell lentelliptical, with smooth surface and irregular network; pores roundish, very small, scarcely as broad as the bars; about eight to nine on the half meridian, six to seven on the half equator. Proportion of the three axes = 3 : 4 : 6. Internal four gates elliptical. Medullary shell spherical, scarcely one-third as broad as the cortical shell. (This small species may be only the medullary shell of some other Larcoid, the cortical shell of which is not yet formed.)

Dimensions.--Length of the cortical shell 0.06, breadth 0.04, height 0.03; pores and bars about 0.004; medullary shell 0.013.

Habitat.--Pacific, central area, Station 265, depth 2900 fathoms.

Genus 273. Larnacidium,[312] n. gen.

Definition.--#Larnacida# with a simple lentelliptical cortical shell, connected by the lateral wings of a latticed transverse girdle with the simple, spherical or lentelliptical, medullary shell. Surface armed with radial spines.

{619}The genus Larnacidium has the same shell-formation as the foregoing Larnacilla, and differs from it only in the possession of radial spines on the surface, which in all known species exhibit a symmetrical disposition. From the nearly allied genus Larcidium it differs in the characteristic mode of connection between the two shells, owing to the different kind of growth. In Larcidium this connection is effected only by radial beams, whereas in Larnacidium (as in all Larnacida) by two lateral latticed tubes, the wings of the primary transverse girdle.

1. Larnacidium staurobelonium, n. sp.

Cortical shell smooth, with four strong conical, radial spines in the lateral plane, opposite in pairs, two on the poles of the principal and two on the poles of the transverse axis. Pores subregular, circular, twice as broad as the bars; about twelve on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell spherical, one-third as broad as the cortical shell.

Dimensions.--Length of the cortical shell 0.12, breadth 0.09, height 0.06; pores 0.008, bars 0.04; medullary shell 0.03.

Habitat.--North Pacific Station 244, depth 2900 fathoms.

2. Larnacidium hexabelonium, n. sp.

Cortical shell thorny, with six strong, three-sided pyramidal, radial spines, lying opposite in pairs on the poles of the three dimensive axes. Pores subregular, circular, three times as broad as the bars; about fourteen on the half meridian. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell spherical, one-third as broad as the cortical shell.

Dimensions.--Length of the cortical shell 0.14, breadth 0.11, height 0.08; pores 0.01, bars 0.003; medullary shell 0.04.

Habitat.--South Pacific, Station 295, depth 1500 fathoms.

3. Larnacidium polybelonium, n. sp.

Cortical shell very spiny, with numerous (twenty to thirty or more) larger thin radial spines, about as long as the shell. Pores irregular, twice to five times as broad as the bars; about sixteen on the half meridian. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell lentelliptical, half as large as the cortical shell.

Dimensions.--Length of the cortical shell 0.11, breadth 0.09, height 0.07; pores 0.004 to 0.01, bars 0.002; length of the medullary shell 0.06, breadth 0.05, height 0.04.

Habitat.--Western Tropical Pacific, Station 225. depth 4475 fathoms.

Subfamily 2. LARNACALPIDA, Haeckel.

Definition.--#Larnacida# with a double, trizonal, Larnacilla-shaped medullary shell, enclosed in the central capsule, and enveloped by a simple or double, latticed or spongy, lentelliptical, cortical shell.

{620}Genus 274. Larnacalpis,[313] n. gen.

Definition.--#Larnacida# with a simple lentelliptical cortical shell, without radial spines. Medullary shell double, Larnacilla-shaped.

The genus Larnacalpis represents the most simple form of the sub-family Larnacalpida, and is very important as the common original form of all those #Larcoidea# in which a double Larnacilla-shaped medullary shell is surrounded by a simple, perfectly closed, latticed, lentelliptical cortical shell. Therefore the same typical, trizonal, lentelliptical shell, which in Larnacilla represents the external envelop (or cortical shell) of the central capsule, here in Larnacalpis becomes enclosed as an internal nucleus (or medullary shell) in the interior of the central capsule, and this latter becomes overgrown by a new lentelliptical cortical shell. The connection between the two shells of Larnacalpis is either effected by a number of radial beams (e.g., in Larnacalpis triaxonia by six beams situated in the three dimensive axes), or by two lateral, latticed, tube-like wings, which are repetitions of the smaller lateral wings connecting its external shell with the internal medullary shell (as in Larnacalpis lentellipsis). The latter species may be regarded as a Pylonium with a completely latticed shell.

1. Larnacalpis lentellipsis, n. sp. (Pl. 50, figs. 2, 2_a_, 2_b_).

Cortical shell with thorny surface and irregular network; pores roundish, twice to four times as broad as the bars; about sixteen on the half meridian, twelve on the half equator. Proportion of the three dimensive axes = 2 : 3 : 4. Medullary shell one-third as large as the cortical, with four elliptical internal gates, connected with it by two opposite beams in the principal axis and by two latticed wings in the transverse axis; therefore between the two shells are four large kidney-shaped gates, halved by the polar beams (as in Octopyle).

Dimensions.--Length of the cortical shell (or principal axis) 0.14, breadth (or transverse axis) 0.11, height (or sagittal axis) 0.07; pores 0.01 to 0.02, bars 0.005; length of the medullary shell 0.05, breadth 0.04, height 0.03.

Habitat.--Pacific, central area, Station 273, depth 2600 fathoms.

2. Larnacalpis phacodiscus, n. sp.

Cortical shell with thorny surface and regular network; pores circular, twice as broad as the bars; about ten on the half meridian, eight on the half equator. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell half as large as the cortical, with four kidney-shaped internal gates.

Dimensions.--Length of the cortical shell 0.13, breadth 0.11, height 0.09; pores 0.012, bars 0.006; length of the medullary shell 0.06, breadth 0.045, height 0.03.

Habitat.--North Pacific, Station 253, depth 3125 fathoms.

{621}3. Larnacalpis macrococcus, n. sp.

Cortical shell with spiny surface and regular network; pores circular, small, of the same breadth as the bars; about twenty-two on the half meridian, nineteen on the half equator. Proportion of the three axes = 2 : 3 : 4. Medullary shell two-thirds as large as the cortical, with four wide internal semicircular gates.

Dimensions.--Length of the cortical shell 0.1, breadth 0.075, height 0.05; pores and bars 0.003; length of the medullary shell 0.066, breadth 0.05, height 0.032.

Habitat.--Western Tropical Pacific, Station 224, depth 1850 fathoms.

4. Larnacalpis subsphærica, n. sp.

Cortical shell with rough surface and irregular network; roundish pores twice to five times as broad as the bars; about twenty-four on the half meridian, twenty-one on the half equator. Proportion of the three axes = 1.2 : 1.3 : 1.4. Medullary shell half as large as the cortical, with four elliptical internal gates.

Dimensions.--Length of the cortical shell 0.14, breadth 0.13, height 0.12; pores 0.004 to 0.01, bars 0.002; length of the medullary shell 0.08, breadth 0.07, height 0.06.

Habitat.--Pacific, central area, Station 266, depth 2750 fathoms.

5. Larnacalpis triaxonia, n. sp. (Pl. 50, fig. 3).

Cortical shell with smooth surface and peculiar network, composed of four meridian rows of larger pores (five large elliptical pores on each half meridian, the largest in the equator) and numerous small irregular pores between them. Proportion of the three axes = 2 : 3 : 4. Medullary shell with four semicircular internal gates, about one-fourth as large as the cortical, connected with it by six thin radial beams, opposite in pairs in the three dimensive axes.

Dimensions.--Length of the cortical shell 0.14, breadth 0.1, height 0.07; large pores 0.03, small pores 0.002 to 0.01, bars 0.002 to 0.01; length of the medullary shell 0.04, breadth 0.03, height 0.02.

Habitat.--Pacific, central area, Station 263, depth 2650 fathoms.

Genus 275. Larnacantha,[314] n. gen.

Definition.--#Larnacida# with a simple lentelliptical cortical shell, armed with symmetrically disposed radial spines. Medullary shell double, Larnacilla-shaped.

The genus Larnacantha has the same characteristic shell-formation as the foregoing Larnacalpis, and differs from it only in the possession of radial spines, which are symmetrically distributed on the surface in a definite order. Commonly these spines are external prolongations of the internal radial beams, which connect the double Larnacilla-shaped medullary shell with the simple lentelliptical cortical shell.

{622}1. Larnacantha dissacantha, n. sp.

Cortical shell smooth, with two large cylindrical spines, opposite on the poles of the principal axis, and somewhat longer than it. Pores regular, circular, three times as broad as the bars; about eleven on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell one-third as large as the cortical shell.

Dimensions.--Length of the cortical shell (principal axis) 0.13, breadth (transverse axis) 0.1, height (sagittal axis) 0.07; pores 0.009, bars 0.003; length of the Larnacilla-shaped medullary shell 0.045.

Habitat.--North Pacific, Station 256, depth 2950 fathoms.

2. Larnacantha stauracantha, n. sp.

Cortical shell smooth, with four large conical spines in the lateral plane, two larger opposite on the poles of the principal, two smaller on those of the transverse axis. Pores regular, circular, twice as broad as the bars; about seventeen on the half meridian. Proportion of the three axes = 3 : 3.5 : 4. Medullary shell one-third as large as the cortical shell.

Dimensions.--Length of the cortical shell 0.15, breadth 0.13, height 0.11; pores 0.008, bars 0.004; length of the medullary shell 0.05.

Habitat.--Pacific, central area, Station 274, surface.

3. Larnacantha quadricornis, n. sp.

Cortical shell spiny, with four strong, horn-like curved spines in the lateral plane, opposite in pairs on the poles of the crossed diagonal axes. Pores irregular, roundish, twice to four times as broad as the bars; about fourteen on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell one-third as large as the cortical shell.

Dimensions.--Length of the cortical shell 0.14, breadth 0.11, height 0.07; pores 0.006 to 0.012, bars 0.003; length of the medullary shell 0.05.

Habitat.--Pacific, central area, Station 270, surface.

4. Larnacantha hexacantha, n. sp. (Pl. 50, fig. 4).

Cortical shell thorny, with six strong conical radial spines in the lateral plane, two opposite on the poles of the principal axis, four others opposite in pairs on the poles of the two crossed diagonal axes. Pores with peculiar distribution; twelve large elliptical pores (nearly of the size of the medullary shell) symmetrically disposed in four crossed meridians (between the sagittal and the lateral meridians), separated by bands of smaller irregular pores. Proportion of the three axes = 3 : 4 : 5. Medullary shell hexagonal, one-third as large as the cortical shell.

Dimensions.--Length of the cortical shell 0.14, breadth 0.11, height 0.08; large pores 0.04, small pores 0.003 to 0.01, bars 0.004; length of the medullary shell 0.05.

Habitat.--Pacific, central area, Station 263, depth 2650 fathoms.

{623}5. Larnacantha bicruciata, n. sp. (Pl. 50, fig. 5).

Cortical shell thorny, in the lateral plane with eight strong conical radial spines, alternating with eight smaller spines; four of the eight stronger spines opposite on the poles of the principal and transverse axes (in the figure 5, by mistake, not represented large enough), four others between those, opposite on the poles of the two crossed diagonal axes. Pores with a peculiar disposition; on both flat sides of the lentellipsis an elliptical ring of eight large elliptical pores (alternating with the eight stronger radial spines), separated by bands of smaller irregular pores. Proportion of the three axes = 2 : 3 : 4. Medullary shell nearly half as long as the cortical shell.

Dimensions.--Length of the cortical shell 0.16, breadth 0.13, height 0.08; large pores 0.03, small pores 0.003 to 0.01, bars 0.006; length of the medullary shell 0.07.

Habitat.--Indian Ocean, surface, Madagascar (Rabbe).

6. Larnacantha octacantha, n. sp.

Cortical shell thorny, with eight long and thin, cylindrical, radial spines, lying opposite in pairs in two crossed diagonal planes. Pores irregular, roundish, twice to five times as broad as the bars; about sixteen on the half meridian. Proportion of the three axes = 1 : 1-1/3 : 2. Medullary shell scarcely one-fourth as long as the cortical shell. (This species resembles closely the common Tetrapyle octacantha, from which it seems to be developed by a complete over-growing of the four gates, which become closed by a network connecting the free edges of the transverse and lateral girdles.)

Dimensions.--Length of the cortical shell 0.18, breadth 0.13, height 0.1; pores 0.005 to 0.015, bars 0.003; length of the medullary shell 0.04.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

7. Larnacantha cladacantha, n. sp.

Cortical shell very spiny, with eight longer ramified spines, lying opposite in pairs in two crossed diagonal planes; each spine with two to six irregular, lateral branches. Pores irregular, roundish, twice to three times as broad as the bars; about twelve on the half meridian. Proportion of the three axes = 5 : 6 : 7. Medullary shell nearly half as long as the cortical shell. (Differs from the foregoing by the branching spines end the larger medullary shell.)

Dimensions.--Length of the cortical shell 0.15, breadth 0.13, height 0.11; pores 0.01 to 0.015, bars 0.005; length of the medullary shell 0.07.

Habitat.--Indian Ocean, surface, Cocos Islands (Rabbe).

8. Larnacantha prismatica, n. sp. (Pl. 50, fig. 6).

Cortical shell smooth, four-sided prismatic, with eight short, parallel, three-sided pyramidal spines; these lie opposite in pairs in four parallel longitudinal lines, as prolongations of the four {624}lateral edges of the prism, and arise from its eight corners. Pores regular, circular, three times as broad as the bars; about fourteen on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell half as long as the cortical shell.

Dimensions.--Length of the cortical shell 0.11, breadth 0.07, height 0.05; pores 0.006, bars 0.002; length of the medullary shell 0.06.

Habitat.--Pacific, central area, Station 263, depth 2650 fathoms.

9. Larnacantha decacantha, n. sp.

Cortical shell thorny, with ten short and stout, conical, radial spines, two opposite on the poles of the principal axis (as prolongations of inner axial beams), eight others opposite in pairs in two crossed diagonal planes. Pores irregular, roundish, twice to four times as broad as the bars; about sixteen on the half meridian. Proportion of the three axes = 3 : 3.75 : 4. Medullary shell about one-third as long as the cortical shell.

Dimensions.--Length of the cortical shell 0.16, breadth 0.15, height 0.12; pores 0.008 to 0.016, bars 0.004; length of the medullary shell 0.06.

Habitat.--North Atlantic, Station 354, surface.

10. Larnacantha dodecantha, n. sp.

Cortical shell nearly smooth, but with twelve strong conical radial spines; four in the lateral plane opposite in pairs (two on the poles of the principal, and two on the poles of the transverse axis); eight others opposite in pairs in two crossed diagonal planes. Pores with a peculiar disposition: twelve large elliptical pores in two crossed meridian planes (alternating with the twelve spines), separated by bands of irregular small pores. Proportion of the three axes = 1 : 1.5 : 2. Medullary shell hexagonal, one-third as long as the cortical shell.

Dimensions.--Length of the cortical shell 0.15, breadth 0.11, height 0.08; large pores 0.03, small pores 0.005 to 0.01, bars 0.003; length of the medullary shell 0.05.

Habitat.--Pacific, central area, Station 265, depth 2900 fathoms.

11. Larnacantha drymacantha, n. sp.

Cortical shell very spiny, on the whole surface covered with a forest of numerous (thirty to fifty or more) large branched spines, about the length of the shell; each spine with three to nine lateral branches, simple or forked (very similar to Cromyodrymus abietinus, Pl. 30, fig. 6). Pores very irregular, roundish. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell half as long as the cortical shell.

Dimensions.--Length of the cortical shell 0.16, breadth 0.13, height 0.1; pores 0.005 to 0.015, bars 0.03; length of the medullary shell 0.08.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

{625}Genus 276. Larnacoma,[315] n. gen.

Definition.--#Larnacida# with double lentelliptical cortical shell, without radial spines. Medullary shell double, Larnacilla-shaped.

The genus Larnacoma has originated from the nearly allied Larnacalpis by duplication of the cortical shell. Whilst in both genera the connection between the Larnacilla-shaped medullary shell and the primary cortical shell is the same, many short radial beams arise from the surface of the latter in Larnacoma, which at constant equal distances from it unite by a network forming the secondary or outer cortical shell. It differs from the similar Druppulida (Cromyodruppa) by the sagittal flattening of the lentelliptical shell and the Larnacilla-form of the double medullary shell.

1. Larnacoma lentellipticum, n. sp.

Shell with smooth surface and elliptical perimeter, one and a third times as long as broad. All four shells lentelliptical. Distance between the two cortical shells about twice as great as the distance of the inner cortical and outer medullary shell. Network of both outer shells irregular, with large roundish pores, twice to six times as broad as the bars.

Dimensions.--Length (or principal axis) of the first (innermost) shell 0.03, second 0.08, third 0.16, fourth (outermost) 0.27, breadth (or transverse axis) corresponding--(A) 0.02, (B) 0.05, (C) 0.11, (D) 0.2.

Habitat.--South Atlantic, Station 323, depth 1900 fathoms.

2. Larnacoma quadruplex, n. sp.

Shell with thorny surface and elliptical perimeter, one and a fifth times as long as broad. All four shells lentelliptical. Distance between the two cortical shells somewhat smaller than the distance between the inner cortical and outer medullary shell. Network of both outer shells irregular, with large roundish pores, twice to ten times as broad as the bars.

Dimensions.--Length of the first shell 0.02, second 0.06, third 0.15, fourth 0.24; breadth corresponding--(A) 0.016, (B) 0.04, (C) 0.11, (D) 0.2.

Habitat.--South Atlantic, Station 335, depth 1425 fathoms.

3. Larnacoma hexagonium, n. sp.

Shell with thorny surface and hexagonal perimeter, as long as broad. All four shells hexagonal, connected by six piercing radial beams (two in the principal axis, four others in two crossed diagonals). Distance between the two cortical shells somewhat greater than the distance between the inner cortical and outer medullary shell. Network of both outer shells subregular, with small circular pores, twice as broad as the bars.

{626}Dimensions.--Length of the first shell 0.02, second 0.05, third 0.09, fourth 0.16; breadth corresponding--(A) 0.015, (B) 0.035, (C) 0.065, (D) 0.12.

Habitat.--South Atlantic, west of Tristan da Cunha, Station 332, depth 2200 fathoms.

Genus 277. Larnacospongus,[316] n. gen.

Definition.--#Larnacida# with spongy lentelliptical cortical shell, without radial spines. Medullary shell double, Larnacilla-shaped.

The genus Larnacospongus differs from the nearly allied genera Larnacalpis and Larnacoma by the spongy texture of the lentelliptical cortical shell whilst the enclosed medullary shell in both genera is the same trizonal Larnacilla-shell. Therefore Larnacospongus (and the following nearly related Larnacostupa) can be derived directly by development of a spongy envelop either from Larnacilla and Larnacalpis, or from Trizonium and Amphipyle. But some species of these spongy genera appear to be derived rather from Tetrapyle or Pylonium, perhaps also from Cubotholus. Their phylogenetic origin may be explained in different ways.

1. Larnacospongus larnacillifer, n. sp.

Cortical shell lentelliptical, one and a half times as long as broad, with rough surface and rather loose spongy framework, directly enclosing a trizonal Larnacilla-shell of the same form, but of only one-third its size.

Dimensions.--Length of the whole shell 0.17, breadth 0.12; length of the medullary shell 0.06, breadth 0.04.

Habitat.--South Atlantic, east coast of Patagonia, Station 319, surface.

2. Larnacospongus tetrapylifer, n. sp.

Cortical shell lentelliptical, one and a third times as long as broad, with thorny surface; composed of an outer envelop of loose spongy framework and an inner lattice-shell with four kidney-shaped gates, like Tetrapyle; the latter encloses a trizonal medullary shell of one-fourth its size.

Dimensions.--Length of the whole shell 0.22, breadth 0.16; length of the medullary shell 0.045, breadth 0.035.

Habitat.--South Atlantic, west of Tristan da Cunha, Station 332, surface.

{627}Genus 278. Larnacostupa,[317] n. gen.

Definition.--#Larnacida# with spongy lentelliptical cortical shell, with radial spines on the surface. Medullary shell double, Larnacilla-shaped.

The genus Larnacostupa differs from the preceding Larnacospongus only in the possession of radial spines, covering either the whole surface irregularly or disposed in a certain symmetrical order.

1. Larnacostupa octacantha, n. sp.

Cortical shell lentelliptical, with thorny surface, and rather dense, irregular, spongy framework, which arises from an inner latticed cortical shell, like that of Tetrapyle or Pylonium. This latter is twice as large as the enclosed Larnacilla-shell. Eight long and thin, cylindrical, radial spines, opposite in pairs in two diagonal planes. (Seems to be the common Tetrapyle octacantha, enveloped by an outer spongy framework mantle.)

Dimensions.--Length of the whole shell (without spines) 0.22, breadth 0.16; length of the medullary shell 0.06, breadth 0.04.

Habitat.--Indian Ocean, Madagascar, Rabbe, surface.

2. Larnacostupa spinosa, n. sp.

Cortical shell lentelliptical, about one and a half times as long as broad, with very lax and irregular spongy framework, arising from a nearly quadrangular lattice-shell like that of Tetrapyle; this latter encloses a Larnacilla-shell of half its size. Whole surface covered with thin bristle-like radial spines, of about the length of the shell.

Dimensions.--Length of the whole shell (without spines) 0.18, breadth 0.12; length of the medullary shell 0.05, breadth 0.035.

Habitat.--Antarctic Ocean, off Kerguelen, Station 150, surface.

3. Larnacostupa dendrophora, n. sp.

Cortical shell nearly spherical, scarcely longer than broad, with lax, irregular spongy framework, arising from a lentelliptical trizonal medullary shell (like Larnacilla). Whole surface covered with thin arborescent radial spines, about half as long as the shell, each spine with three to six irregular branches.

Dimensions.--Length of the whole shell (without spines) 0.15, breadth 0.13; length of the medullary shell 0.07, breadth 0.04.

Habitat.--Antarctic Ocean, Station 154, surface.

{628}Family XXVI. #PYLONIDA#, Haeckel, 1881 (Pl. 9).

Pylonida, Haeckel, 1881, Prodromus, p. 463.

Definition.--#Larcoidea# with regular, incompletely latticed cortical shell, distinguished by two to four or more symmetrically disposed gates or large fissures remaining between one to three latticed dimensive girdles (perpendicular one to another). One, two, or three concentric systems of such girdles (each system with three girdles) may be developed.

The family #Pylonida# is the most important and interesting among all the #Larcoidea#, not only because it is much richer in different and peculiar forms than the other families of this section, but also because it has direct and very complex relations to all the other families of #Larcoidea#. It is even possible that the Pylonida represent the original ancestral group of the whole section, and that the apparently simpler group of the Larcarida must be derived from the former by retrogressive metamorphosis.

Till the year 1881 the family Pylonida, which here now exhibits ten genera with eighty-six species, was only represented by one single species, accurately described and extensively illustrated by Johannes Müller in 1858, the well known and widely distributed cosmopolitan Tetrapyle octacantha (Abhandl. d. k. Akad. d. Wiss. Berlin, p. 33, Taf. iii.). A slight modification of it was afterwards described by Ehrenberg as Schizomma quadrilobum (Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, Taf. ii. fig. 12). A more accurate description of it, with a good explanation of its characteristic growth, was given in 1879 by Richard Hertwig in his Organismus der Radiolarien (pp. 52-54, Taf. iv. figs. 7, 8; Taf. vi. figs. 2, 5). In my Prodromus (1881, p. 463) I constituted for a large number of allied species, detected in the Challenger collection, the special family Pylonida, and distinguished among it twelve different genera. However, I think it now better to restrict the definition of the family as given in the above definition, and to remove from it a number of genera formerly with it united, as the genera Triopyle and Hexapyle, appertaining to the #Discoidea#.

The characteristic type of all true Pylonida is clearly demonstrated by their peculiar mode of growth, the consequence of which is the imperfect lattice-work of the fenestrated larcoid shell. This remarkable growth is effected by the development of elliptical latticed girdles (or rings), which enclose a quite simple, spherical, subspherical, or lentelliptical primordial shell. The girdles lie in three different planes, perpendicular to one another, and are of different sizes; each girdle being somewhat larger than the foregoing and somewhat smaller than the following girdle. Between these latticed girdles remain on the surface of the shell large openings or "gates," which are not closed by network, and it is just the symmetrical disposition and form of these open "gates," separated and enclosed by the fenestrated girdles, which give to the Pylonida their characteristic appearance.

{629}To understand clearly this peculiar constitution of the Pylonida-shell by a system of alternating girdles, developing one after the other it is indispensable to pay careful attention to the three different elliptical dimensive planes, which characterise all #Larcoidea#, and to the three different dimensive axes, which bisect those planes. The girdle which first develops around simple primordial shell or central chamber is the transverse girdle, lying in the equatorial plane; then comes, secondly, the lateral girdle, lying in the lateral plane; and thirdly follows the sagittal girdle, lying in the sagittal or median plane. The three simplest genera of the Pylonida--Monozonium, Dizonium, Trizonium--represent these three different stages, with one, two, or three girdles. These three genera constitute the first subfamily, Haplozonaria (with one single system of girdles); all three girdles lie in the surface of a simple lentelliptical cortical shell.

From this first subfamily the other two subfamilies of Pylonida must be derived, by repetition of the same characteristic process of growth. In the Diplozonaria a second system of girdles has been developed, constituting a second (outer) cortical shell of lentelliptical form, concentric with the first. Also in this second system the transverse girdle is first developed, secondly the lateral girdle, thirdly the sagittal girdle. The three genera Amphipyle, Tetrapyle (with Octopyle), and Pylonium represent these three different stages of growth.

Commonly the growth of the Pylonida stops with the completion of the second system but sometimes the same process is once repeated and a third system of girdles is formed, constituting a third lentelliptical shell; in this case also the succession of the three latticed girdles is the same; firstly the (third) transverse girdle is formed, secondly the (third) lateral girdle, and thirdly the (third) sagittal girdle. Each of these three girdles of the third system encloses concentrically the corresponding girdles of the second and first system. The three corresponding genera of this third subfamily (Triplozonaria) are Amphipylonium, Tetrapylonium, and Pylozonium. But in general this highest number of girdles (nine) is very seldom reached; commonly the growth of the Pylonida stops with five girdles (Tetrapyle and Octopyle). More than nine girdles I have never observed, though there remains the possibility of the apposition of a fourth system owing to the peculiar imperfect character of the growth itself.

The central or primordial chamber of the shell, with which in all Pylonida the shell-building commences, is a quite simple, very small fenestrated shell. Commonly one sees on the surface only five to ten small pores (three to four on the diameter). Its form seems to be sometimes spherical, sometimes elongated, ellipsoidal or probably lentelliptical. It may be originally a small Cenolarcus. This simple central chamber, the true "medullary shell" of the small Haplozonaria, is quite different from the medullary shell of the larger Diplozonaria, and particularly of the well-known Tetrapyle. The former observers, J. Müller as well as R. Hertwig, have described in these forms also the medullary shell as a simple spherical or oblong body. But a careful {630}comparison of many hundred specimens of them and of their dimensions, has convinced me that this was an error, and that the small spherical or elliptical medullary shell of Tetrapyle and the other Diplozonaria possesses already the same complex structure, composed of a system of three girdles, as Trizonium and Larnacilla. Whilst in the Haplozonaria probably the simple central chamber only represents the medullary shell (enclosed in the central capsule), and the first system of girdles (complete in Trizonium) the external cortical shell, with the progressive growth this latter becomes enclosed in the central capsule and so constitutes the "trizonal medullary shell" of the Diplozonaria and Triplozonaria.

A very difficult matter is the mode of connection between the cortical and medullary shell. In most of the Pylonida it seems that the first or transverse girdle (in each system) is produced by the formation of two lateral wings or chambers (one on each side of the medullary shell), so that each wing (or half girdle) represents a short and wide, nearly cylindrical tube, the axis of which (with free openings on both poles) is parallel to the principal axis of the medullary shell. In this case (probably the ordinary one) both principal faces of the medullary shell itself (dorsal and ventral face) constitute the middle part of the first girdle whilst its lateral parts are formed by the wings (comparable to the lateral chambers of Amphitholus).

In the second case (probably a much rarer one) there is a free ring-shaped space between the medullary shell and the first (transverse) girdle, and both are connected by a small number of very short and small radial beams (R. Hertwig, loc. cit., p. 52, line 19 to 21 from above). This mode of connection would be the same as is common between the concentric shells of the #Sphæroidea# and #Prunoidea#. The distinction between these two different modes of connection is often very difficult.

The second or lateral girdle is commonly not in direct connection with the medullary shell, or only by some scattered radial beams (mainly in the principal axis). This lateral guide arises by prolongation of both wings of the transverse girdle in the lateral plane, so that from both sides (right and left) they become united on the poles of the principal axis. The minor axis of the elliptical lateral ring (thus formed) is therefore the major axis of the foregoing (transverse) elliptical ring; the major axes of both are perpendicular one to another. The major axis of the lateral ring is the principal (or longitudinal) axis of the whole body.

The third or sagittal girdle becomes developed from the second almost in the same manner as the second from the first. On both poles of the principal axis two latticed wings arise from the lateral girdle, growing further in the direction of an elliptical ring, which represents the perimeter of the sagittal plane or median plane. These wings are already mentioned by J. Müller as "prominent roofs, protecting the gates of the Tetrapyle-shell." If these roofs grow towards the equatorial plane of the shell and become united in pairs on the poles of the sagittal axis, the third girdle becomes {631}complete. R. Hertwig supposes that the minor axis of this sagittal girdle is constantly at the same time the major axis of the lateral girdle, but this is not always the case. Very often the size of both these girdles is nearly the same, or one is not much larger than the other. In this case the principal axis of the body is the major axis of the second as well as of the third girdle.

The characteristic "gates" of the Pylonida, or the large wide openings in their cortical shell, remaining between the crossed latticed girdles, are in general roundish, sometimes nearly circular, commonly more elliptical, kidney-shaped or semilunar, their special form varying much according to the different form of the girdles. The narrowest part of each girdle, or its "isthmus," in the case of the halves of the transverse girdle is commonly at their origin from the medullary shell, in the case of the halves of the lateral girdle at the poles of the principal axis, and in the case of the halves of the sagittal girdle at the poles of the sagittal axis. The number of the gates is quite constant in the different genera. If only one girdle (the transverse) be developed, we find only two large gates, between the two wings on the poles of the principal axis (in Monozonium, Amphipyle, Amphipylonium). In all other cases there are four gates (determining the original name "Tetrapyle"), as well if only two or if all three girdles be completed. If two girdles be complete (in Dizonium, Tetrapyle, Tetrapylonium) the four gates lie opposite in pairs on the sagittal faces (two anterior and two posterior gates), and are limited by the transverse and lateral girdles. If all three girdles be complete (in Trizonium, Pylonium, Pylozonium) the four gates lie opposite in pairs on the lateral faces (two dorsal and two ventral gates), and are limited by the sagittal and the transverse girdles. If we turn the shell through an angle of 90°, we have the same aspect as in the former group. A sagittal septum sometimes becomes developed, beginning with two polar beams, rising from the poles of the principal axis. If these polar beams become branched and connected with the middle part of the lateral girdle, we get a latticed vertical septum, which divides the four gates of Tetrapyle into eight gates, Octopyle.

The lattice-work of the Pylonida is commonly very variable and irregular, with roundish meshes of very unequal size, therefore without value in the determination of the species. Commonly the outside of the shell is thorny, and often distinguished by larger radial spines, symmetrically disposed. We can separate these into two groups; "dimensive" spines, lying in one of the three dimensive axes (principal, transverse, or sagittal), and "diagonal" spines, lying crossed in pairs in diagonal axes. Among these latter eight diagonal wing-spines, which arise from the lateral edges of the four gates, are particularly remarkable; they are not only characteristic of Tetrapyle octacantha, but also of a large number of other Pylonida, and form the starting-point for many specific forms.

The shell of the Pylonida is characterised by extraordinary variability and great {632}inclination to individual abnormalities, formation of varieties and transitions into other families, hence derived, as Larnacida, Tholonida, Lithelida, &c.

The central capsule in all Pylonida, in which I could observe it, was a true lentellipsis (or a "triaxial ellipsoid" in the geometrical sense, with the three unequal isopolar axes of the "rhombic octahedron"). In the living Pylonida it is commonly coloured pink or scarlet. During growth its dimensions are probably more or less changed, and perhaps the axes alternate. Regarding the relation of the central capsule to the skeleton, we can distinguish two different groups, quite as in the nearly allied Larnacida. In the Haplozonaria (as also in the Larnacillida) the central capsule encloses only the central chamber and is enveloped by the first system of girdles, whereas in the Diplozonaria and Triplozonaria (as in the Larnacalpida) that "trizonal shell" becomes enclosed (as the "medullary shell") in the central capsule, which is now enveloped by the second system of girdles as the "cortical shell."

Synopsis of the Genera of Pylonida.

------------------------------------------------------------------------- I. Subfamily Haplozonaria. One system of girdles. Medullary shell simple, spherical or lentelliptical; cortical shell simple, with one, two, or three girdles. ------------------------------------------------------------------------- Cortical shell only with one latticed (transverse) girdle, 279. Monozonium.

Cortical shell with two perfect girdles (transverse and lateral), 280. Dizonium.

Cortical shell with three perfect girdles (transverse, lateral, and sagittal), 281. Trizonium. ------------------------------------------------------------------------- II. Subfamily Diplozonaria. Two systems of concentric girdles. Medullary shell trizonal, with three perfect girdles; cortical shell simple, with one, two or three girdles. ------------------------------------------------------------------------- Cortical shell only with one perfect (transverse) girdle, 282. Amphipyle.

Cortical shell with two { Four gates simple, 283. Tetrapyle. perfect girdles (the { transverse and lateral).{ Four gates bisected by { a sagittal septum, 284. Octopyle.

Cortical shell with three perfect girdles (transverse, lateral, and sagittal), 285. Pylonium. ------------------------------------------------------------------------- III. Subfamily Triplozonaria. Three systems of concentric girdles. Medullary shell trizonal, with three perfect girdles, quite as the inner cortical shell; outer cortical shell with one, two, or three girdles. ------------------------------------------------------------------------- Outer cortical shell (third system) only with one perfect (transverse) girdle, 286. Amphipylonium.

Outer cortical shell with two perfect girdles (transverse and lateral), 287. Tetrapylonium.

Outer cortical shell with three perfect girdles (transverse, lateral, and sagittal), 288. Pylozonium.

Subfamily 1. HAPLOZONARIA, Haeckel.

Definition.--#Pylonida# with one single system of fenestrated girdles (with one, two, or three girdles, lying in one lentelliptical face).

{633}Genus 279. Monozonium,[318] n. gen.

Definition.--#Pylonida# with simple, spherical or subspherical, central chamber, surrounded by one single (transverse) latticed girdle.

The genus Monozonium is the most simple and primitive of all Pylonida, and may be regarded as their common ancestral form; it may probably be derived phylogenetically either directly from Cenosphæra or from Lentellipsis, either by apposition of two imperfect lateral chambers, or by surrounding it with an equatorial latticed girdle. This transverse girdle is composed of three parts, the central chamber and two lateral wings, which represent two short hollow latticed tubes, the axes of which are parallel to the principal axis. On both principal sides (on the anterior and posterior faces) there are two large open gates as in Amphipyle. If we imagine the openings of the tube-shaped lateral wings closed by lattice-work, Monozonium becomes transformed into Tholartus, the most simple form of Tholonida. Probably in all Pylonida the ontogeny of the shell begins with the formation of a Monozonium.

Subgenus 1. Monozonaris, Haeckel.

Definition.--Shell smooth or rough, without radial spines or thorns.

1. Monozonium primordiale, n. sp.

Central chamber of the shell spherical, smooth, with three to four pores on the half equator. Both wings of the girdle of the same breadth, but of twice the length of the central chamber, with three to four longitudinal rows of pores. No radial spines.

Dimensions.--Diameter of the central chamber 0.02; breadth of the wings 0.02, length 0.04; pores and bars 0.003.

Habitat.--Pacific, central area, Station 271, surface.

2. Monozonium alatum, n. sp. (Pl. 9, fig. 1).

Central chamber of the shell lentelliptical, smooth, one and a half times as long as broad, with three to four pores on the half equator. Both wings of the girdle twice as broad, and somewhat longer than the central chamber, with five to six longitudinal rows of pores. No radial spines.

Dimensions.--Length of the central chamber 0.03, breadth 0.02; breadth of the wings 0.04, length 0.05; pores and bars 0.004.

Habitat.--North Pacific, Station 241, surface.

Monozonium hartingii = Haliomma amphiaspis, Harting, 1863 (L. N. 18, p. 15, pl. 2, fig. 43).

{634}Subgenus 2. Monozonitis, Haeckel.

Definition.--Shell with radial spines or thorns, symmetrically disposed.

3. Monozonium pleurostylum, n. sp.

Central chamber spherical, smooth, with four to five pores on the half equator. Both wings of the girdle of the same breadth, but somewhat longer than the central chamber, with four to five longitudinal rows of pores. On the poles of the lateral axis two opposite strong conical spines (one in the middle of each wing).

Dimensions.--Diameter of the central chamber 0.025; breadth of the wings 0.025, length 0.03; pores and bars 0.005.

Habitat.--Pacific, central area, Station 265, surface.

4. Monozonium amphistylum, n. sp.

Central chamber lentelliptical, one and a half times as long as broad, with three to four pores on the half equator. Breadth and length of each wing somewhat greater than that of the central chamber. On the latter two strong conical spines, opposite on the poles of the principal or longitudinal axis.

Dimensions.--Length of the central chamber 0.03, breadth 0.02; breadth of the wings 0.025, length 0.04; pores and bars 0.004.

Habitat.--South Atlantic, Station 332, surface.

5. Monozonium staurostylum, n. sp.

Central chamber lentelliptical, one and a third times as long as broad, with four to five pores on the half equator. Both wings of the girdle have the same breadth, but one and a half times the length of the central chamber. Four conical radial spines, two opposite on the poles of the lateral, two on the poles of the principal axis.

Dimensions.--Length of the central chamber 0.028, breadth 0.021; breadth of the wings 0.02, length 0.04.

Habitat.--South Pacific, Station 295, surface.

Genus 280. Dizonium,[319] n. gen.

Definition.--#Pylonida# with simple, spherical or subspherical, central chamber, surrounded by two crossed latticed girdles, one smaller (primary) transverse and one larger (secondary) lateral girdle.

The genus Dizonium differs from the preceding Monozonium in the possession of two crossed elliptical lattice-girdles. The smaller girdle, immediately surrounding the {635}central chamber, is the transverse girdle (the single girdle of Monozonium). On the poles of its major axis (the transverse axis) it is connected with the larger girdle, the elliptical perimeter of which circumscribes the lateral plane. The minor axis of this latter is the major axis of the former. Between the two crossed girdles remain four larger openings or gates, quite as in Tetrapyle. But whilst in Tetrapyle the enclosed medullary shell is a trizonal Larnacilla-shell, here in Dizonium it is a simple spherical or lentelliptical chamber.

Subgenus 1. Dizonaris, Haeckel.

Definition.--Shell smooth or rough, without radial spines or thorns.

1. Dizonium circulare, n. sp.

Central chamber of the shell spherical, smooth, with four to five pores on the half equator. Lateral girdle circular, three times as broad as the former. Four gates semilunar, twice as broad as high. No radial spines.

Dimensions.--Diameter of the central chamber 0.02, of the lateral girdle 0.06; height of the gates 0.02, breadth 0.04.

Habitat.--Pacific, central area, Station 274, surface.

2. Dizonium ellipticum, n. sp.

Central chamber of the shell elliptical, smooth, with three to four pores on the half equator. Lateral girdle elliptical, three times as long and broad as the central chamber. Four gates kidney-shaped, twice as broad as high. No radial spines.

Dimensions.--Length of the central chamber 0.03, breadth 0.02; length of the lateral girdle 0.09, breadth 0.06; height of the gates 0.02, breadth 0.038.

Habitat.--South Pacific, Station 288, surface.

3. Dizonium transversum, n. sp.

Central chamber of the shell spherical, rough, with five to six pores on the half equator. Lateral girdle transverse-elliptical, so that its longer axis corresponds to the lateral axis of the transverse girdle, and equals four times the diameter of the central chamber. Four gates kidney-shaped, four times as broad as high. No radial spines.

Dimensions.--Diameter of the central chamber 0.02; length of the lateral girdle 0.05, breadth 0.08; height of the gates 0.01, breadth 0.04.

Habitat.--Pacific, central area, Station 274, depth 2750 fathoms.

{636}Subgenus 2. Dizonitis, Haeckel.

Definition.--Shell with radial spines or thorns, symmetrically disposed.

4. Dizonium pleuracanthum, n. sp. (Pl. 9, fig. 2).

Central chamber of the shell nearly spherical, smooth. Lateral girdle elliptical, one and a third times as long as broad, three times as long as the central chamber. Four gates transverse-elliptical, one and a half times as broad as high. Two conical spines, opposite on the poles of the lateral axis.

Dimensions.--Diameter of the central chamber 0.03; length of the lateral girdle 0.1, breadth 0.075; height of the gates 0.026, breadth 0.04.

Habitat.--Western Tropical Pacific, Station 224, depth 1850 fathoms.

5. Dizonium amphacanthum, n. sp.

Central chamber elliptical. Lateral girdle elliptical, twice as long as broad. Four gates heart-shaped, about as high as broad. Two conical spines, opposite on the poles of the principal axis.

Dimensions.--Length of the central chamber 0.03, breadth 0.02; length of the lateral girdle 0.1, breadth 0.05; height and breadth of the gates 0.03.

Habitat.--Pacific, central area, Station 270, depth 2925 fathoms.

6. Dizonium stauracanthum, n. sp. (Pl. 9, fig. 3).

Central chamber spherical. Lateral girdle elliptical, one and a third times as long as broad. Four gates elliptical, one and a half times as broad as high, halved by an axial beam (as in Octopyle). Four conical radial spines opposite in pairs, two on the poles of the principal, two on the poles of the transverse axis.

Dimensions.--Diameter of the central chamber 0.025; length of the lateral girdle 0.09, breadth 0.06; height of the gates 0.024, breadth 0.036.

Habitat.--South Atlantic, Station 332, depth 2200 fathoms.

7. Dizonium octacanthum, n. sp.

Central chamber spherical. Lateral girdle elliptical, one and a half times as long as broad. Four gates kidney-shaped, twice as broad as high. Eight radial spines, opposite in pairs in two crossed diagonal planes.

Dimensions.--Diameter of the central chamber 0.02; length of the lateral girdle 0.075, breadth 0.05; height of the gates 0.02, breadth 0.04.

Habitat.--Pacific, central area, Station 272, surface.

{637}Genus 281. Trizonium,[320] n. gen.

Definition.--#Pylonida# with simple, spherical or subspherical, central chamber, surrounded by three latticed girdles, one smaller (primary) transverse, one larger (secondary) lateral, and one (tertiary) sagittal girdle.

The genus Trizonium represents the most highly developed form of the Haplozonaria, with three complete elliptical latticed girdles, crossed at right angles and lying in the perimeter of the three dimensive planes. Commonly the first (transverse) girdle is the smallest, immediately connected with the spherical or lentelliptical central chamber. The minor axis of the second (lateral) girdle is identical with the major axis of the first girdle. The third (sagittal) girdle is either larger than both others, or intermediate between them. If the four gates between the girdles become afterwards closed by lattice-work, the "trizonal shell" of Trizonium passes over into the typical Larnacilla, the ancestral form of a great many #Larcoidea#.

Subgenus 1. Trizonaris, Haeckel.

Definition.--Shell smooth or rough, without radial spines or thorns.

1. Trizonium tricinctum, n. sp. (Pl. 9, fig. 4).

Central chamber of the shell elliptical. Lateral girdle elliptical, one and a half times as long as broad. Four gates kidney-shaped, one and a half times as broad as high. Ten to eleven pores on the half equator, fourteen to sixteen on the half meridian of the lentelliptical shell. No radial spines on the surface.

Dimensions.--Length of the central chamber 0.024, breadth 0.016; length of the lateral girdle 0.075, breadth 0.05; height of the four gates 0.026, breadth 0.04.

Habitat.--Pacific, central area, Station 272, depth 2600 fathoms.

2. Trizonium constrictum, n. sp.

Central chamber elliptical. Lateral girdle violin-shaped, on both sides in the middle constricted, twice as long as broad. Four gates transverse-elliptical, twice as broad as high. Eight to nine pores on the half equator, twelve to thirteen on the half meridian. No radial spines.

Dimensions.--Length of the central chamber 0.03, breadth 0.02; length of the lateral girdle 0.09, breadth (in the middle) 0.045; height of the gates 0.022, breadth 0.044.

Habitat.--Pacific, central area, Station 263, surface.

{638}3. Trizonium hexagonium, n. sp.

Central chamber spherical. Lateral girdle hexagonal, with parallel sides, twice as long as broad. Four gates triangular, twice as broad as high. Eleven to twelve pores on the half equator, sixteen to eighteen on the half meridian. No radial spines.

Dimensions.--Diameter of the central chamber 0.025; length of the lateral girdle 0.08, breadth 0.04; height of the gates 0.018, breadth 0.036.

Habitat.--Pacific, central area, Station 266, depth 2750 fathoms.

4. Trizonium octogonium, n. sp.

Central chamber spherical. Lateral girdle octagonal; two lateral sides of the octagon twice as long as the two polar sides and the four diagonal sides. Four gates hexagonal, one and a half times as broad as high. Nine to ten pores on the half equator, twelve to fourteen on the half meridian. No radial spines.

Dimensions.--Diameter of the central chamber 0.02; length of the lateral girdle 0.01, breadth 0.07; height of the gates 0.04, breadth 0.06.

Habitat.--Indian Ocean, surface; Ceylon, Haeckel.

Subgenus 2. Trizonitis, Haeckel.

Definition.--Shell with radial spines or thorns, symmetrically disposed.

5. Trizonium pleurobelonium, n. sp.

Central chamber spherical. Lateral girdle elliptical, one and a third times as long as broad. Four gates nearly circular. Ten to eleven pores on the half equator, fifteen to sixteen on the half meridian. Two opposite conical spines on the poles of the lateral axis.

Dimensions.--Diameter of the central chamber 0.02; length of the lateral girdle 0.08, breadth 0.06; height and breadth of the gates 0.025.

Habitat.--South Atlantic, off Buenos Ayres, Station 323, depth 1900 fathoms.

6. Trizonium amphibelonium, n. sp.

? Echinosphæra datura, R. Hertwig (partim), 1879, Organismus d. Radiol., p. 54, Taf. iv. figs. 8, 8_a_.

Central chamber lentelliptical. Lateral girdle lanceolate, nearly one and a half times as long as broad. Four gates subtriangular. Eight to nine pores on the half equator, ten to twelve on the half meridian. Two opposite thin and long spines on the poles of the principal axis, numerous shorter radial spines on the whole surface. Possibly this species is identical with one of the three different #Larcoidea# which R. Hertwig has described as Echinosphæra datura. His fig. 8, Taf. iv., would be the aspect from the sagittal girdle.

{639}Dimensions.--Length of the central chamber 0.04, breadth 0.025; length of the lateral girdle 0.11, breadth 0.08; height of the gates 0.03, breadth 0.04.

Habitat.--Mediterranean (Genoa), Haeckel, (Messina), R. Hertwig, surface; Tropical Atlantic, Station 348, surface.

7. Trizonium staurobelonium, n. sp.

Central chamber spherical, with two opposite polar beams. Lateral girdle elliptical, one and a half times as long as broad. Four gates transverse-elliptical, half as high as broad. Ten to eleven pores on the half equator, fourteen to fifteen on the half meridian. Four conical radial spines, two on the poles of the lateral, two on the poles of the principal axis.

Dimensions.--Diameter of the central chamber 0.02; length of the lateral girdle 0.075, breadth 0.05; height of the gates 0.014, breadth 0.028.

Habitat.--North Pacific, Station 241, depth 2300 fathoms.

8. Trizonium hexabelonium, n. sp.

Central chamber elliptical. Lateral girdle hexagonal, one and a half times as long as broad. Four gates rhombic, two-thirds as high as broad. Eight to nine pores on the half equator, twelve to thirteen on the half meridian. Six radial spines in the lateral plane, opposite in pairs on the six corners of the lateral girdle (two principal and four diagonal).

Dimensions.--Length of the central chamber 0.024, breadth 0.018; length of the lateral girdle 0.06, breadth 0.04; height of the gates 0.02, breadth 0.03.

Habitat.--Pacific, central area, Station 263, depth 2650 fathoms.

9. Trizonium octobelonium, n. sp.

Central chamber elliptical. Lateral girdle hexagonal, one and one-third times as long as broad. Four gates kidney-shaped or nearly rhombic, twice as broad as high. Eleven to twelve pores on the half equator, sixteen to seventeen on the half meridian. Eight radial spines, opposite in pairs in two crossed diagonal planes. (An intermediate stage between Dizonium octacanthum and Amphipyle octostyle.)

Dimensions.--Length of the central chamber 0.03, breadth 0.024; length of the lateral girdle 0.09, breadth 0.07; height of the gates 0.025, breadth 0.05.

Habitat.--Indian Ocean, Madagascar, Rabbe, surface.

10. Trizonium decabelonium, n. sp.

Central chamber elliptical. Lateral girdle hexagonal, one and a half times as long as broad. Four gates rhombic, twice as broad as high. Twelve to thirteen pores on the half equator, seventeen to eighteen on the half meridian. Ten radial spines, two opposite on the two poles of the principal axis, eight others opposite in pairs in two crossed diagonal planes.

{640}Dimensions.--Length of the central chamber 0.04, breadth 0.03; length of the lateral girdle 0.12, breadth 0.08; height of the gates 0.03, breadth 0.06.

Habitat.--North Atlantic, Station 353, surface.

11. Trizonium dodecabelos, n. sp.

Central chamber spherical. Lateral girdle octagonal, nearly twice an long as broad. Four gates hexagonal, one and a half times as broad as high. Nine to ten pores on the half equator, fifteen to sixteen on the half meridian. Twelve radial spines, four in the lateral plane, in pairs on both sides of the poles of the principal axis, eight others opposite in pairs in two crossed diagonal axes.

Dimensions.--Diameter of the central chamber 0.025; length of the lateral girdle 0.1, breadth 0.06; height of the gates 0.033, breadth 0.05.

Habitat.--Pacific, central area, Station 272, surface.

Subfamily 2. DIPLOZONARIA, Haeckel.

Definition.--#Pylonida# with two concentric systems of fenestrated girdles, lying in two concentric lentelliptical faces (every one system with one to three girdles, lying in one lentelliptical face).

Genus 282. Amphipyle,[321] Haeckel, 1881, Prodromus, p. 463.

Definition.--#Pylonida# with trizonal lentelliptical medullary shell, surrounded by one single (transverse) latticed cortical girdle.

The genus Amphipyle opens the large series of Diplozonaria, comprising all Pylonida, the shell of which is composed of two concentric systems of latticed girdles; the first system constituting the characteristic "trizonal medullary shell" or "Larnacilla-shell;" the second system composed of one to three girdles of the second order. The first system lies inside, the second outside the central capsule. In Amphipyle only the first (transverse) girdle of the second system becomes developed, and therefore on both poles of the principal axis are two large open gates. Amphipyle repeats the two-winged form of Monozonium; but whilst the medullary shell in this latter is a simple central chamber, it is here a trizonal Larnacilla-shell.

Subgenus 1. Amphipylissa, Haeckel.

Definition.--Cortical shell smooth or thorny, but without large, symmetrically disposed spines.

{641}1. Amphipyle aceros, n. sp.

Cortical shell quite smooth, without any spines or thorns. Both lateral wings (or opposite half girdles) semilunar, with convex lateral crest, three times as long as broad; twice as broad as the trizonal lentelliptical medullary shell.

Dimensions.--Length of the medullary shell 0.05, breadth 0.03; length of each lateral wing (or principal dimension of the latticed girdle) 0.18, breadth of it (or transverse dimension of each girdle-tube) 0.06.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

2. Amphipyle stenoptera, n. sp.

Cortical shell smooth, without spines. Both lateral wings of the same breadth as the lentelliptical medullary shell, but five times as long as broad, prolonged on both ends into cylindrical latticed tubes, with rectilinear lateral crest.

Dimensions.--Length of the medullary shell 0.06, breadth 0.04; length of each cylindrical lateral wing 0.2, breadth 0.04.

Habitat.--South Atlantic, off Ascension Island, Station 343, surface.

3. Amphipyle platyptera, n. sp.

Cortical shell thorny, but without larger spines. Both lateral wings nearly triangular, very broad and short, four times as broad as the medullary shell between them, and only twice as long as broad, with rectilinear lateral crest.

Dimensions.--Length of the medullary shell 0.05, breadth 0.25; length of each lateral wing 0.18, breadth 0.09.

Habitat.--Indian Ocean, Ceylon, Haeckel, surface.

Subgenus 2. Amphipylura, Haeckel.

Definition.--Cortical shell armed with large, symmetrically disposed spines.

4. Amphipyle amphiceros, n. sp.

Cortical shell with two conical spines on the poles of the longitudinal axis (of the lentelliptical medullary shell), without other large spines, but with small thorns on the surface; two to three longitudinal rows of irregular, roundish pores on each half wing of the cortical girdle.

Dimensions.--Length of the medullary shell (or principal axis) 0.06, breadth (or transverse axis) 0.04; length of each lateral wing 0.2, breadth of it 0.05.

Habitat.--Western Tropical Pacific, Station 222, surface.

{642}5. Amphipyle tetraceros, n. sp. (Pl. 9, fig. 5).

Cortical shell with smooth surface, and with four strong conical spines in the lateral plane, opposite in pairs on the ends of the concave lateral crests (one pair on the end-points of the lateral line of each wing); four to five longitudinal rows of irregular, roundish pores on each half wing of the cortical girdle. Surface of the medullary shell spiny.

Dimensions.--Length of the medullary shell 0.08, breadth of the same 0.05; length of each lateral wing 0.16, breadth 0.04.

Habitat.--Pacific, central area, Station 271, surface.

6. Amphipyle stauroceros, n. sp.

Cortical shell with four strong conical spines, two on the poles of the longitudinal axis, two opposite on the poles of the transverse axis (perpendicular to the former). Three to four longitudinal rows of irregular, roundish pores on each half wing of the cortical girdle, about six pores in the longest row. Lateral crest convex.

Dimensions.--Length of the medullary shell 0.05, breadth 0.03; length of each lateral wing 0.15, breadth 0.08.

Habitat.--Pacific, central area, Station 268, depth 2900 fathoms.

7. Amphipyle amphiptera, n. sp. (Pl. 9, fig. 7).

Cortical shell with six strong conical spines, lying in the lateral plane in three parallel longitudinal lines; two on the poles of the longitudinal axis, two others on the poles of the wing axes, which are parallel to the former. Two to three longitudinal rows of irregular, roundish pores on each half wing of the cortical girdle, about eight pores in the longest row. Lateral crest convex, thorny.

Dimensions.--Length of the medullary shell 0.06, breadth 0.045; length of each lateral wing 0.09, breadth 0.035.

Habitat.--Western Tropical Pacific, Station 224, surface.

8. Amphipyle hexaceros, n. sp.

Cortical shell thorny, with six strong conical spines lying in the lateral plane; two on the poles of the lateral axis (in the central point of each wing), two on the end-points of the triangular crest of each wing (on both poles of the longitudinal wing-axis).

Dimensions.--Length of the medullary shell 0.06, breadth 0.04; length of each lateral wing 0.13, breadth 0.07.

Habitat.--South Pacific, Station 291, surface.

{643}9. Amphipyle octoceros, n. sp.

Cortical shell thorny, with eight long radial spines, lying in two crossed diagonal planes, opposite in pairs. These eight horns are the prolongations of the anterior and posterior edges of each wing, on both sides of its lateral plane; they are of great importance, as appearing (by heredity) in many other Pylonida (e.g., in Tetrapyle octacantha). Lateral crest of each wing without spines, slightly convex.

Dimensions.--Length of the medullary shell 0.07, breadth 0.05; length of each lateral wing 0.15, breadth 0.06.

Habitat.--Pacific, central area, Stations 270 to 274, surface.

10. Amphipyle cladoceros, n. sp.

Cortical shell spiny, with eight strong ramified radial spines, lying in the same two crossed diagonal planes as in the preceding species. It differs from this in the ramification of the eight horns, which bear six to nine irregular lateral branches, partly simple, partly bifurcate. Lateral crest of each wing spiny, convex.

Dimensions.--Length of the medullary shell 0.06, breadth 0.045; length of each lateral wing (without spines) 0.2, breadth 0.09.

Habitat.--Indian Ocean, surface, Madagascar, Rabbe.

11. Amphipyle decaceros, n. sp.

Cortical shell spiny, with ten strong conical spines; eight lying in two crossed diagonal planes, in the same disposition (opposite in pairs) as in both preceding species; two others opposite on the poles of the principal axis, arising from both poles of the medullary shell (columella-beams). Spiny crest of the wings convex, semilunar.

Dimensions.--Length of the medullary shell 0.04, breadth 0.03; length of each lateral wing 0.12, breadth 0.04.

Habitat.--North Atlantic, Station 354, surface.

12. Amphipyle dodecaceros, n. sp.

Cortical shell thorny, with twelve large cylindrical spines; eight lying in two crossed diagonal planes, in the same disposition (opposite in pairs) as in the three preceding species; four others crossed at right angles in the lateral plane, two opposite on the poles of the principal, two on the poles of the lateral axis (the latter shorter). Both lateral wings nearly rhombic.

Dimensions.--Length of the medullary shell 0.06, breadth 0.04; length of the lateral wings 0.15, breadth 0.05.

Habitat.--South Atlantic, coast of Brazil, Rabbe, surface.

{644}13. Amphipyle callizona, n. sp. (Pl. 9, fig. 6).

Cortical shell smooth, with sixteen strong and short conical spines, lying opposite in pairs in two crossed diagonal planes; each lateral wing four-sided prismatic, its lateral face concave, both ends truncated, and each end provided with four divergent spines. Length of the wings somewhat greater, but breadth smaller, than that of the medullary shell.

Dimensions.--Length of the medullary shell 0.07, breadth 0.05; length of the lateral wings 0.09, breadth 0.03.

Habitat.--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Genus 283. Tetrapyle,[322] J. Müller, 1858, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 154.

Definition.--#Pylonida# with trizonal lentelliptical medullary shell, surrounded by two crossed latticed cortical girdles, one smaller (primary) transverse, and one larger (secondary) lateral girdle. Four gates between the two cortical girdles simple, without a sagittal septum.

The genus Tetrapyle, till 1881 the only known genus of the whole family, was founded by Johannes Müller in 1858, and clearly illustrated by the Mediterranean (and common cosmopolitan) Tetrapyle octacantha, hitherto the best known type of this family. Afterwards (1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 832) Ehrenberg founded the genus Schizomma for a nearly allied form, which exhibits only slight specific differences (compare my Monograph, 1862, p. 434). Some good remarks on the structure of this typical genus and its relations to other Pylonida are to be found in Richard Hertwig's Organismus, &c., 1879, p. 52, but the true trizonal structure of the medullary shell in this genus was not recognised by him, so that his description agrees more with Dizonium. We confine here the genus Tetrapyle to those Pylonida for which Tetrapyle octacantha of J. Müller remains the determining type; the cortical shell is composed only of two perfect lattice-girdles (the transverse and lateral), between which four wide gates remain open. This structure is similar to that of Dizonium; but whilst here the medullary shell is a simple central chamber, in Tetrapyle it is a complete trizonal or Larnacilla-shell.

Subgenus 1. Tetrapylissa, Haeckel.

Definition.--Cortical shell smooth or thorny, but without large, symmetrically disposed spines.

{645}1. Tetrapyle circularis, n. sp. (Pl. 9, fig. 8).

Cortical shell rough, without radial spines. Lateral girdle circular, therefore the longitudinal axis is equal to the transverse. Four gates kidney-shaped, twice as broad as high. In each half wing of the transverse girdle six to seven longitudinal rows of irregular, roundish pores.

Dimensions.--Medullary shell 0.05 long, 0.04 broad; cortical shell 0.15 long and broad; gates 0.04 high, 0.08 broad.

Habitat.--Pacific, central area, Station 263, surface.

2. Tetrapyle circopyle, n. sp.

Cortical shell smooth, without radial spines. Lateral girdle elliptical, one and a half times as long as broad. Four gates nearly circular. On each half wing of the transverse girdle four to five rows of subregular, circular pores. (Similar to Tetrapyle pleuracantha, Pl. 9, fig. 9, but without lateral spines.)

Dimensions.--Medullary shell 0.04 long, 0.03 broad; cortical shell 0.16 long, 0.11 broad; gates 0.05 high and broad.

Habitat.--Pacific, central area, Station 268, depth 2900 fathoms.

3. Tetrapyle quadriloba, Haeckel.

Tetrapyle quadriloba, Haeckel, 1862, Monogr. d. Radiol., p. 436.

Schizomma quadrilobum, Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 815; Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, Taf. x. figs. 12-14.

Cortical shell thorny, without regular, radial spines. Lateral girdle elliptical, one and a half times as long as broad. Four gates nearly circular. On each half wing of the transverse girdle three to four rows of irregular, roundish pores.

Dimensions.--Medullary shell 0.06 long, 0.04 broad; cortical shell 0.16 long, 0.1 broad; diameter of the gates 0.05.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Indian Ocean, Pacific, surface.

4. Tetrapyle nephropyle, n. sp.

Cortical shell thorny, without radial spines. Lateral girdle elliptical, one and a third times as long as broad. Four gates kidney-shaped, nearly twice as broad as high, with two prominent polar spines on the poles of the longitudinal axis of the medullary shell. On each half wing of the transverse girdle three to four longitudinal rows of large roundish pores.

Dimensions.--Medullary shell 0.06 long, 0.04 broad; cortical shell 0.24 long, 0.18 broad; gates 0.05 high, 0.08 broad.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

{646}5. Tetrapyle cardiopyle, n. sp.

Cortical shell rough, without radial spines. Lateral girdle with hexagonal contour, nearly cylindrical in the middle part, conical at both ends, twice as long as broad. Four gates heart-shaped, about as high as broad. On each half wing of the transverse girdle three to four longitudinal rows of subregular, polygonal pores.

Dimensions.--Medullary shell 0.04 long, 0.02 broad; cortical shell 0.14 long, 0.07 broad; gates 0.05 high and broad.

Habitat.--Eastern Tropical Atlantic, Station 348, depth (2450) fathoms.

Subgenus 2. Tetrapylura, Haeckel.

Definition.--Cortical shell armed with large, symmetrically disposed spines.

6. Tetrapyle fusiformis, n. sp.

Cortical shell rough, with two strong conical spines on the poles of the longitudinal axis. Lateral girdle spindle-shaped, one and a half times as long as broad. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle four to five longitudinal rows of irregular, roundish pores.

Dimensions.--Medullary shell 0.07 long, 0.05 broad; cortical shell 0.18 long, 0.12 broad; gates 0.04 high, 0.08 broad.

Habitat.--Western Tropical Atlantic, Mexican Gulf Stream, depth 1500 fathoms, Schaffner.

7. Tetrapyle pleuracantha, n. sp. (Pl. 9, fig. 9).

Cortical shell rough, with two strong conical spines on the poles of the transverse axis. Lateral girdle elliptical, one and half times as long as broad. Four gates subcircular or nearly hexagonal, about as high as broad. On each half wing of the transverse girdle three to four longitudinal rows of very irregular pores.

Dimensions.--Medullary shell 0.045 long, 0.035 broad; cortical shell 0.16 long, 0.11 broad; gates 0.045 high and broad.

Habitat.--Western Tropical Pacific, off New Guinea, Stations 222 to 224, depths 1850 to 2450 fathoms.

8. Tetrapyle transversa, n. sp.

Cortical shell thorny, with two strong conical lateral spines on the poles of the transverse axis. Lateral girdle elliptical, only four-fifths as long as broad. Four gates elliptical, twice as broad as high, with two prominent spines on the poles of the longitudinal axis of the medullary shell. On each half wing of the transverse girdle five to six longitudinal rows of subregular, roundish pores. (Similar to Octopyle transversa, but without sagittal septum and with stronger lateral spines.)

{647}Dimensions.--Medullary shell 0.05 long, 0.035 broad; cortical shell 0.12 long, 0.15 broad; gates 0.03 high, 0.06 broad.

Habitat.--Southern Pacific, Station 290, surface.

9. Tetrapyle cruciata, n. sp.

Cortical shell smooth, with four strong radial spines, two on the poles of the longitudinal axis, two on the poles of the transverse axis. Lateral girdle nearly circular, quite as long as broad. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle five to six rows of subregular, circular pores.

Dimensions.--Medullary shell 0.06 long, 0.05 broad; cortical shell 0.16 long and broad; gates 0.05 high, 0.09 broad.

Habitat.--South Atlantic, Station 330, surface.

10. Tetrapyle staurophora, n. sp.

Cortical shell thorny, with four strong radial spines, two on the poles of the longitudinal axis, two on the poles of the transverse axis. Lateral girdle elliptical, one and a half times as long as broad. Four gates nearly hexagonal, quite as high as broad. On each half wing of the transverse girdle three to four longitudinal rows of irregular, roundish pores.

Dimensions.--Medullary shell 0.06 long, 0.04 broad; cortical shell 0.18 long, 0.12 broad; gates 0.08 high and broad.

Habitat.--Western Tropical Atlantic, coast of Brazil, Rabbe, surface.

11. Tetrapyle quadricornis, n. sp.

Cortical shell thorny, with four strong horn-like curved spines, lying in the lateral plane and converging in pairs towards the poles of the transverse axis. Lateral girdle elliptical, one and a third times as long as broad. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle four to five rows of irregular, roundish pores. (May be only the young form of Pylonium quadricorne, Pl. 9, fig. 14.)

Dimensions.--Medullary shell 0.05 long, 0.04 broad; cortical shell 0.16 long, 0.12 broad; gates 0.03 high, 0.07 broad.

Habitat.--Pacific, central area, Stations 270 to 274, surface.

12. Tetrapyle tetracantha, n. sp.

Cortical shell thorny, with four strong radial spines lying in the lateral plane and in pairs in its two crossed diagonal axes. Lateral girdle elliptical, constricted in the middle, nearly twice as long as broad. Four gates kidney-shaped, one and a half times as broad as high. On each half wing of the transverse girdle three to four longitudinal rows of large, irregular, roundish pores. {648}(Similar to Tetrapylonium quadrangulare, Pl. 49, fig. 15, but without a sagittal girdle and with stronger lateral spines.)

Dimensions.--Medullary shell 0.06 long, 0.04 broad; cortical shell 0.18 long, 0.1 broad; gates 0.007 high, 0.01 broad.

Habitat.--North Atlantic, Canary Islands, Station 353, surface.

13. Tetrapyle quadrigata, n. sp.

Cortical shell thorny, with four brush-like groups of radial spines on the four diagonal corners of the lateral plane, opposite in pairs in diagonal axes. Lateral girdle nearly square, somewhat broader than long. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle five to six longitudinal rows of irregular, roundish pores.

Dimensions.--Medullary shell 0.06 long, 0.04 broad; cortical shell 0.14 long, 0.15 broad; gates 0.03 high, 0.07 broad.

Habitat.--Pacific, central area, Station 270, surface.

14. Tetrapyle octacantha, J. Müller.

Tetrapyle octacantha, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 33, Taf. ii. figs. 1-6.

Tetrapyle octacantha, Haeckel, 1862, Monogr. d. Radiol., p. 435.

Tetrapyle octacantha, R. Hertwig, 1879, Organismus d. Radiol., p. 52, Taf. iv. fig. 7, Taf. vi. figs. 2, 5, 5_a._

Cortical shell thorny, with eight long and thin, cylindrical radial spines, lying in two crossed diagonal planes, opposite in pairs. These eight characteristic diagonal spines (or "angular spines") are the same as in Amphipyle octoceros and many other Pylonida, and arise as prolongations of the proximal edges of the four gates (or of the lateral wings on the eight points, where they are intersected by the edges of the lateral ring). This cosmopolitan, widely distributed and very variable species was a long time the only known species of all the Pylonida, and very accurately first described (1858) by Johannes Müller, afterwards (1879) by R. Hertwig. But in the descriptions of these authors also some different species (such as the following) may be confounded with the true typical Tetrapyle octacantha. The four gates of this species are transverse-elliptical or almost triangular, nearly twice as broad as high.

Dimensions.--Length of the medullary shell 0.04, breadth 0.03; length of the cortical shell 0.18, breadth 0.13; height of the gates 0.05, breadth 0.08.

Habitat.--Cosmopolitan; very common in all warmer seas, Mediterranean, Atlantic, Indian, Pacific, surface.

15. Tetrapyle cladacantha, n. sp.

Cortical shell thorny, with eight strong ramified radial spines, lying opposite in pairs in two crossed diagonal planes, as in the preceding species. It differs from this by the peculiar ramification of the eight spines, which bear two to eight simple or furcate lateral branches arising under {649}right angles (already commencing in a transitional variety of Tetrapyle octacantha, J. Müller, loc. cit., Taf. ii. figs. 5, 6). Four gates transverse-elliptical, one and a half times as broad as high.

Dimensions.--Medullary shell 0.05 long, 0.04 broad; cortical shell 0.16 long, 0.13 broad; gates 0.05 high, 0.08 broad.

Habitat.--Mediterranean (Corfu), Haeckel, surface.

16. Tetrapyle pluteus, Haeckel.

Tetrapyle octacantha, var., J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. iii. figs. 7-12.

Cortical shell thorny, with eight strong radial spines, lying opposite in pairs, as in the two foregoing species. On the distal edge each of the four triangular gates is protected by a prominent roof of lattice-work (or "pluteus"), which arises from the distal part of the lateral girdle and connects the two angular diagonal spines of each gate. Therefore the shell assumes the characteristic form very well represented by J. Müller in his fig. 11 (seen from the lateral side) and fig. 7 (seen from the pole of the principal axis).

Dimensions.--Medullary shell 0.04 long, 0.03 broad; cortical shell 0.15 long, 0.11 broad; gates 0.045 high, 0.07 broad.

Habitat.--Mediterranean, Atlantic, Stations 348 to 353, &c., surface.

17. Tetrapyle turrita, n. sp. (Pl. 9, fig. 10).

Cortical shell smooth, but with ten strong conical spines, two on the poles of the principal axis, eight others symmetrically distributed on both sides of the distal edge of the four roundish gates, and directed towards the transverse axis. Lateral girdle lanceolate, twice as long as broad.

Dimensions.--Medullary shell 0.05 long, 0.04 broad; cortical shell 0.2 long, 0.1 broad; gates 0.05 high, 0.07 broad.

Habitat.--Pacific, central area, Station 274, depth 2750 fathoms.

18. Tetrapyle dodecaceros, n. sp.

Cortical shell thorny, with twelve stronger conical spines, eight diagonal spines in two crossed planes (as in Tetrapyle octacantha), and four others in the lateral plane, in pairs on both sides of a deep sagittal constriction of the quadrangular lateral girdle. Four gates kidney-shaped, twice as broad as high. On each half wing of the transverse girdle five to six longitudinal rows of irregular, roundish pores.

Dimensions.--Medullary shell 0.06 long, 0.04 broad; cortical shell 0.18 long, 0.14 broad; gates 0.04 high, 0.08 broad.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

{650}Genus 284. Octopyle,[323] Haeckel, 1881, Prodromus, p. 464.

Definition.--#Pylonida# with trizonal lentelliptical medullary shell, surrounded by two crossed, latticed, cortical girdles; one smaller (primary) transverse, and one larger (secondary) lateral girdle. Four gates between the two cortical girdles divided by a sagittal septum into eight gates.

The genus Octopyle comprises those Pylonida which are distinguished from the nearly allied Tetrapyle by the development of a sagittal septum, dividing the four gates of the latter into eight separate gates. The septum begins with the formation of two axial rods or columellæ, which afterwards become branched; the branches communicating one with another and with the middle parts of the lateral girdle (on the poles of the principal axis), there is formed a latticed septum in the sagittal plane, which separates more or less incompletely the right and left halves of the shell. The four gates of Tetrapyle become halved by this septum, and their number doubled.

Subgenus 1. Octopylissa, Haeckel.

Definition.--Cortical shell smooth or thorny, but without larger symmetrically disposed spines.

1. Octopyle ovulina, n. sp.

Cortical shell lentelliptical, smooth, without thorns. Lateral girdle elliptical, one and a third times as long as broad. Transverse girdle narrow, with two pores on the isthmus (or on the narrowest part of each quadrant). Sagittal septum as long as the elliptical medullary shell. Eight gates egg-shaped.

Dimensions.--Length of the medullary shell 0.05, breadth 0.035; length of the cortical shell 0.16, breadth 0.12.

Habitat.--Pacific, central area, Station 274, surface.

2. Octopyle quadrata, n. sp.

Cortical shell thorny, nearly square, of equal length and breadth. Lateral girdle quadrangular, with rounded edges, of equal length and breadth. Transverse girdle narrow, with three pores on the isthmus. Sagittal septum of the same length as the subspherical medullary shell. Eight gates nearly circular.

Dimensions.--Diameter of the medullary shell 0.04, of the cortical shell 0.14.

Habitat.--Northern Pacific, Station 244, depth 2900 fathoms.

{651}3. Octopyle subglobosa, n. sp.

Cortical shell nearly spherical, thorny, of equal length and breadth. Lateral girdle broad, nearly circular. Transverse girdle broad, with four pores on the isthmus. Sagittal septum shorter than the subspherical medullary shell. Eight gates egg-shaped.

Dimensions.--Diameter of the medullary shell 0.05, of the cortical shell 0.13.

Habitat.--Southern Pacific, Station 300, depth 1375 fathoms.

4. Octopyle transversaria, n. sp.

Cortical shell thorny, transverse-elliptical. Lateral girdle very broad, one and a third times as broad as long. Transverse girdle also very broad, with five pores on the isthmus. Sagittal septum shorter than the elliptical medullary shell. Eight gates small, roundish.

Dimensions.--Length of the medullary shell 0.05, breadth 0.04; length of the cortical shell 0.11, breadth 0.15.

Habitat.--Western Tropical Pacific, Station 224, depth 1850 fathoms.

Subgenus 2. Octopylura, Haeckel.

Definition.--Cortical shell armed with large, symmetrically disposed spines.

5. Octopyle amphistyle, n. sp.

Cortical shell smooth, nearly spindle-shaped, about twice as long as broad. Transverse girdle broad, with four large pores on the isthmus. Lateral girdle lanceolate. Sagittal septa about as long as the medullary shell, prolonged at both poles of the principal axis into two opposite, strong, angular spines. Eight gates obliquely quadrangular.

Dimensions.--Length of the medullary shell 0.07, breadth 0.05; length of the cortical shell 0.2, breadth 0.12.

Habitat.--Pacific, central area, Station 272, depth 2600 fathoms.

6. Octopyle staurostyle, n. sp.

Cortical shell nearly rhombic, smooth, one and a half times as long as broad, with four strong, conical, radial spines, two on the poles of the principal axis (as prolongations of the sagittal septa), two others on the poles of the transverse axis. Transverse girdle narrow, with two pores on the isthmus. Sagittal septa longer than the medullary shell. Eight gates triangular.

Dimensions.--Length of the medullary shell 0.04, breadth 0.03; length of the cortical shell 0.18, breadth 0.12.

Habitat.--Tropical Atlantic, Station 347, depth 2250 fathoms.

{652}7. Octopyle tetrastyle, n. sp.

Cortical shell lentelliptical, with rough surface and four angular radial spines in the lateral plane, opposite in pairs in two crossed diagonals. Lateral girdle nearly rectangular (each angle with one spine), one and a third times as long as broad. Sagittal septum longer than the hexagonal medullary shell. Eight gates egg-shaped.

Dimensions.--Length of the medullary shell 0.05, breadth 0.03; length of the cortical shell 0.16, breadth 0.12.

Habitat.--North Atlantic, Station 354, surface.

8. Octopyle tetraptera, n. sp.

Cortical shell quadrangular, with thorny surface and four latticed wing-like prolongations on the corners of the quadrangle, opposite in pairs in two crossed diagonals, each wing supported by a strong radial spine. Lateral girdle quadrangular, one and a half times as long as broad. On the isthmus of the transverse girdle four pores. Sagittal septum longer than the hexagonal medullary shell. Eight gates triangular.

Dimensions.--Length of the medullary shell 0.07, breadth 0.04; length of the cortical shell 0.24, breadth 0.16.

Habitat.--Pacific, central area, Station 271, surface.

9. Octopyle stenozona, n. sp. (Pl. 9, fig. 11).

Cortical shell quadrangular, with thorny surface, and four conical spines in the lateral plane, on the points, where both cortical girdles are crossed. Lateral girdle very narrow, nearly square, with rounded corners, of equal length and breadth. On the isthmus of the narrow transverse girdle only one pore. Sagittal septum of the same length as the subspherical medullary shell. Eight gates irregular roundish or nearly circular.

Dimensions.--Diameter of the medullary shell 0.04, of the cortical shell 0.14.

Habitat.--Tropical Atlantic, Station 338, depth 1990 fathoms.

10. Octopyle euryzona, n. sp.

Cortical shell nearly quadrangular, very thorny, with four bunches of stronger radial spines on the four corners. Lateral girdle broad, with rounded edges of the quadrangle, little longer than broad. On the isthmus of the broad transverse girdle four pores. Sagittal septum of the same length as the elliptical medullary shell, with many radial beams. Eight gates nearly square.

Dimensions.--Length of the medullary shell 0.05, breadth 0.035; length of the cortical shell 0.16, breadth 0.14.

Habitat.--Southern Atlantic, Station 332, depth 2200 fathoms.

{653}11. Octopyle hexastyle, n. sp.

Cortical shell nearly rectangular, thorny, with six strong radial spines in the lateral plane, two opposite on the poles of the principal axis (prolongations of the principal beam at the sagittal septum), four others on the truncate corners of the quadrangular lateral girdle, which is one and a half times as long as broad. On the isthmus of the broad transverse girdle three pores. Sagittal septum longer than the hexagonal medullary shell. Eight egg-shaped gates.

Dimensions.--Length of the medullary shell 0.05, breadth 0.04; length of the cortical shell 0.18, breadth 0.12.

Habitat.--Northern Atlantic, surface; Canary Islands, Station 9, depth 3150 fathoms.

12. Octopyle sexangulata, n. sp. (Pl. 9, fig. 12).

Cortical shell thorny, hexagonal, with six strong conical radial spines on the six corners of the lateral girdle, lying in the lateral plane, two opposite on the poles of the transverse axis, four others in pairs on both sides of the annular sagittal constriction, which is only twice as long as the elliptical medullary shell. Transverse girdle broad, with five pores on the isthmus. Eight gates roundish, smaller than the medullary shell.

Dimensions.--Length of the medullary shell 0.045, breadth 0.035; length of the cortical shell 0.11, breadth 0.13.

Habitat.--Pacific, central area, Station 270, surface.

13. Octopyle octostyle, n. sp.

Cortical shell elliptical, thorny, with eight long cylindrical radial spines, lying in two crossed diagonal planes, opposite in pairs, quite as in the nearly related Tetrapyle octacantha. It differs from this species by the perfect, latticed, vertical sagittal septum, which divides every gate into two triangular halves. Lateral girdle elliptical, one and a third times as long as broad. Transverse girdle on the isthmus with three pores. Septum longer than the elliptical medullary shell.

Dimensions.--Length of the medullary shell 0.06, breadth 0.045; length of the cortical shell 0.16, breadth 0.12.

Habitat.--South Pacific, Station 288, surface.

14. Octopyle obtecta, n. sp.

Cortical shell quadrangular, thorny, with eight strong diagonal spines, lying in two crossed planes, and arising from the proximal edges of the gates in the same way as in the foregoing species. It differs from this by four prominent latticed roofs, which arise from the distal edge of the gates and connect the diagonal spines of one gate. Octopyle obtecta bears therefore the same relation to Octopyle octostyle that Tetrapyle pluteus does to Tetrapyle octacantha.

Dimensions.--Length of the medullary shell 0.055, breadth 0.04; length of the cortical shell 0.16, breadth 0.12.

Habitat.--Indian Ocean, surface, Madagascar, Rabbe.

{654}15. Octopyle decastyle, n. sp. (Pl. 9, fig. 13).

Cortical shell thorny, nearly quadrangular, with ten stronger radial spines, two opposite on the poles of the principal axis (as prolongations of the axial beams), eight others opposite in pairs in two diagonal planes (as in the foregoing species). Lateral girdle nearly square, with slightly convex lateral faces, slightly concave principal faces. Transverse girdle broad, with four pores on the isthmus. Sagittal septum of the same length as the hexagonal medullary shell. Eight gates elliptical or irregular roundish.

Dimensions.--Length of the medullary shell 0.05, breadth 0.032; diameter of the cortical shell 0.15.

Habitat.--Western Tropical Pacific, Station 224, depth 1850 fathoms.

Genus 285. Pylonium,[324] Haeckel, 1881, Prodromus, p. 464.

Definition.--#Pylonida# with trizonal lentelliptical medullary shell surrounded by three crossed latticed cortical girdles, one smaller (primary) transverse, one larger (secondary) lateral, and one (tertiary) sagittal girdle.

The genus Pylonium is the most highly developed among the Diplozonaria, with six complete latticed girdles, three on the medullary shell, three on the cortical shell, the latter corresponding to the former. In each of the two systems the transverse girdle is smaller than the lateral; the sagittal girdle may be smaller or larger than the lateral girdle. Pylonium repeats the typical form of Trizonium; but whilst in this latter the medullary centre of the shell is a simple spherical chamber, here in Pylonium it is a true trizonal or Larnacilla-shaped medullary shell.

Subgenus 1. Pylonissa, Haeckel.

Definition.--Cortical shell smooth or thorny, but without large, symmetrically disposed spines.

1. Pylonium circozonium, n. sp.

Cortical shell thorny, without radial spines; all its three girdles nearly of the same size, subcircular, very narrow, only with one to two rows of pores. Four gates subcircular.

Dimensions.--Principal axis 0.12, transverse axis 0.11; diameter of the subspherical medullary shell 0.05.

Habitat.--North Pacific, Station 244, depth 2900 fathoms.

{655}2. Pylonium hexazonium, n. sp.

Cortical shell smooth, without symmetrical radial spines. Transverse girdle elliptical, one and a half times as long as broad. Lateral and sagittal girdles nearly circular. Four gates egg-shaped.

Dimensions.--Principal axis 0.16, transverse axis 0.15; diameter of the subspherical medullary shell 0.04.

Habitat.--South Pacific, Station 295, depth 1500 fathoms.

3. Pylonium nephropylium, n. sp.

Cortical shell thorny, without radial spines. All its three girdles elliptical, one and a third times as long as broad. Four gates kidney-shaped, nearly twice as broad as high.

Dimensions.--Principal axis 0.17, transverse axis 0.13; length of the lentelliptical medullary shell 0.04, breadth 0.03.

Habitat.--Pacific, central area, Station 273, depth 2350 fathoms.

Subgenus 2. Pylonura, Haeckel.

Definition.--Cortical shell armed with large, symmetrically disposed spines.

4. Pylonium quadricorne, n. sp. (Pl. 9, fig. 14).

Cortical shell thorny, with four strong horn-like curved spines in the lateral plane. All its three girdles elliptical, one and a third times as long as broad. Four gates kidney-shaped, twice as broad as high. (This species is a further developmental stage of Tetrapyle quadricornis, with perfect sagittal girdle.)

Dimensions.--Principal axis 0.16, transverse axis 0.12; length of the medullary shell 0.05, breadth 0.04.

Habitat.--Pacific, central area, Stations 270 to 274, surface; Indian Ocean, Madagascar, Rabbe, surface.

5. Pylonium octacanthum, n. sp.

Cortical shell thorny, with eight long and thin cylindrical radial spines, lying in two crossed diagonal planes, opposite in pairs, and arising from the eight points where the transverse girdle is crossed by the lateral girdle. All three girdles elliptical, one and a half times as long as broad; four gates triangular. (This species is a further developmental stage of Tetrapyle octacantha, with perfect sagittal girdle.)

Dimensions.--Principal axis 0.18, transverse axis 0.13; length of the medullary shell 0.03 to 0.04.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

{656}6. Pylonium stenozonium, n. sp.

Cortical shell thorny, with eight short conical radial spines, lying in two crossed diagonal planes (as in the foregoing species). All three girdles nearly of the same size, subcircular, very narrow, only with one to two rows of pores. Four gates kidney-shaped.

Dimensions.--Principal axis 0.15, transverse axis 0.14; diameter of the quadrangular medullary shell 0.04.

Habitat.--Equatorial Atlantic, Station 347, surface.

Subfamily 3. TRIPLOZONARIA, Haeckel.

Definition.--#Pylonida# with three concentric systems of fenestrated girdles, lying in three concentric lentelliptical faces (every system with one to three girdles lying in one lentelliptical face).

Genus 286. Amphipylonium,[325] Haeckel, 1881, Prodromus, p. 463.

Definition.--#Pylonida# with trizonal lentelliptical medullary shell, surrounded by a double latticed cortical shell; inner cortical shell Pylonium-shaped, with three perfect crossed girdles; outer cortical shell only represented by a single (transverse) girdle.

The genus Amphipylonium opens the series of Triplozonaria, or of those Pylonida in which the shell is composed of three concentric systems of latticed girdles. The first (and innermost) system represents the complete trizonal medullary shell, which is probably a lentelliptical Larnacilla-shell. The first and intermediate system is formed of a complete trizonal cortical shell of the same form, but much larger (like Pylonium). The third (and outermost) system is represented by one to three latticed girdles, corresponding to the former and forming an outer or second cortical shell. In Amphipylonium (as the most simple form of the Triplozonaria) there is only developed the first (transverse) girdle of the third system. It repeats therefore the form of Amphipyle, the cortical shell of which is here double (Prodromus, 1881, p. 463).

1. Amphipylonium semilunare, n. sp.

Inner cortical shell lentelliptical, one and a half times as long as broad, with smooth surface and four semilunar gates. Transverse girdle of the outer cortical shell with two smooth semilunar wings, with convex, smooth lateral crests; each wing as broad as the transverse girdle of the inner cortical shell and twice as long as its lateral girdle.

Dimensions.--Length of the lentelliptical medullary shell 0.04, breadth 0.03; length of the inner cortical shell 0.15, breadth 0.1; length of each lateral wing of the outer cortical shell 0.3, breadth 0.1.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

{657}2. Amphipylonium spinosissimum, n. sp.

Inner cortical shell lentelliptical, one and a third times as long as broad, with thorny surface and four kidney-shaped gates. Transverse girdle of the outer cortical shell very spiny, with two semilunar wings, with convex thorny lateral crests; each wing one and a half times as broad as the transverse girdle of the inner cortical shell, and one and a half times as long as its lateral girdle.

Dimensions.--Length of the lentelliptical medullary shell 0.05, breadth 0.03; length of the inner cortical shell 0.16, breadth 0.12; length of each lateral wing of the outer cortical shell 0.24, breadth 0.18.

Habitat.--Western Tropical Pacific, Station 225, depth 4475 fathoms.

3. Amphipylonium tetraceros, n. sp.

Inner cortical shell hexagonal, one and a half times as long as broad, with smooth surface and four transverse elliptical gates. Transverse girdle of the outer cortical shell smooth, with rectilinear smooth lateral crests, which are prolonged at both ends into strong conical spines (therefore four spines in the lateral plane); each wing of the same breadth as the transverse girdle of the inner cortical shell, and twice as long as its lateral girdle.

Dimensions.--Length of the hexagonal medullary shell 0.03, breadth 0.02; length of the inner cortical shell 0.12, breadth 0.08; length of each lateral wing of the outer cortical shell 0.24, breadth 0.08.

Habitat.--Northern Pacific, Station 253, depth 3125 fathoms.

4. Amphipylonium octoceros, n. sp.

Inner cortical shell quadrangular, one and a third times as long as broad, with thorny surface and four kidney-shaped gates. Transverse girdle of the outer cortical shell thorny, constricted at the equator, with concave thorny lateral crests, and with eight strong radial spines, opposite in pairs and lying in two crossed diagonal planes; each wing narrower than the transverse girdle of the inner cortical shell and twice as long as its lateral girdle.

Dimensions.--Length of the subspherical medullary shell 0.04, breadth 0.035; length of the inner cortical shell 0.14, breadth 0.11; length of each lateral wing of the outer cortical shell 0.26, breadth 0.09.

Habitat.--Southern Pacific, Station 295, depth 1500 fathoms.

Genus 267. Tetrapylonium,[326] Haeckel, 1881, Prodromus, p. 464.

Definition.--#Pylonida# with trizonal lentelliptical medullary shell, surrounded by a double latticed cortical shell; inner cortical shell Pylonium-shaped, with three perfect crossed girdles; outer cortical shell represented by two crossed girdles, one (smaller) transverse and one (larger) lateral girdle.

{658}The genus Tetrapylonium represents a further developmental stage of the foregoing Amphipylonium; whilst in this latter the outer cortical shell (or the third system of girdles) is formed only by a transverse girdle, here this is crossed by a lateral girdle. Tetrapylonium repeats therefore the typical form of Tetrapyle, but with doubled cortical shell (Prodromus, 1881, p. 464).

1. Tetrapylonium pantellipticum, n. sp.

Outer cortical shell elliptical, one and a third times as long as broad, with smooth surface and four elliptical gates. Inner cortical shell elliptical, with smooth surface and four elliptical gates which repeat the form of the four outer gates, but are of half the size. Transverse girdle broad, with five pores on the isthmus.

Dimensions.--Length (or principal axis) of the first shell (medullary shell) 0.04, breadth (or transverse axis) 0.03; length of the second (or inner cortical) shell 0.12, breadth 0.09; length of the third (or outer cortical) shell 0.18, breadth 0.14.

Habitat.--Pacific, central area, Station 274, depth 2750 fathoms.

2. Tetrapylonium reniforme, n. sp.

Outer cortical shell elliptical, one and a half times as long as broad, with thorny surface and four large kidney-shaped gates. Inner cortical shell of the same form, but one-third smaller, also with four kidney-shaped gates. Transverse girdle small, but with two pores on the isthmus.

Dimensions.--Length of the first (innermost) shell 0.03, breadth 0.02; length of the second (middle) shell 0.14, breadth 0.08; length of the third (outermost) shell 0.2, breadth 0.11.

Habitat.--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

3. Tetrapylonium quadrangulare, n. sp. (Pl. 9, fig. 15).

Outer cortical shell nearly quadrangular, one and a third times as long as broad, with four rounded corners, from which arise in the lateral plane four three-sided pyramidal radial spines, opposite in pairs in two crossed diagonal axes. Surface thorny; four gates elliptical or nearly quadrangular. Inner cortical shell more elliptical, by one half smaller, with broader transverse girdle and four kidney-shaped gates. Medullary shell nearly spherical, of half the size.

Dimensions.--Length of the first shell 0.045, breadth 0.035; length of the second shell 0.1, breadth 0.07; length of the third shell 0.16, breadth 0.11.

Habitat.--South Atlantic, off Tristan da Cunha, Station 332, depth 2200 fathoms.

4. Tetrapylonium octacanthum, n. sp.

Outer cortical shell elliptical, one and a third times as long as broad, with thorny surface, and eight long and thin radial spines arising from the corners of the four triangular gates, and lying {659}opposite in pairs in two crossed diagonal planes. Inner cortical shell of the same shape, but two-thirds smaller, also thorny. Transverse girdle broad, with four pores on the isthmus. (This species appears to be the common Tetrapyle octacantha, with doubled cortical shell.)

Dimensions.--Length of the first shell 0.04, breadth 0.03; length of the second shell 0.16, breadth 0.12; length of the third shell 0.24, breadth 0.18.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

5. Tetrapylonium armatum, n. sp.

Outer cortical shell nearly quadrangular, one and a fourth times as long as broad, with very spiny surface. Between numerous smaller (simple or branched) thorns arise twelve larger radial spines, symmetrically distributed, eight wing-spines crossed in two diagonal planes (as in Tetrapylonium octacanthum) and four corner spines on the four rounded corners of the lateral plane (as in Tetrapylonium quadrangulare). Therefore this species combines the armature of both foregoing species. Four gates kidney-shaped. Inner cortical shell elliptical, smooth, three-fourths smaller.

Dimensions.--Length of the first shell 0.045, breadth 0.035; length of the second shell 0.18, breadth 0.15; length of the third shell 0.25, breadth 0.2.

Habitat.--Pacific, central area, Station 266, depth 2750 fathoms.

Genus 288. Pylozonium,[327] n. gen.

Definition.--#Pylonida# with trizonal lentelliptical medullary shell, surrounded by double latticed cortical shell; inner cortical shell as well as the outer Pylonium-shaped, each with three perfect crossed girdles (transverse, lateral, and sagittal).

The genus Pylozonium is the most highly developed form of the Pylonida, as all three systems of concentric girdles here become fully developed, each system with three perfect girdles. In this genus only among all the Pylonida we find nine complete latticed girdles, and in each of the three dimensive planes three concentric elliptical girdles. The first system forms the medullary shell, the second system the inner cortical shell, and the third system the outer cortical shell.

1. Pylozonium novemcinctum, n. sp.

Outer cortical shell lentelliptical, thorny, one and a third times as long as broad, without radial spines, with four kidney-shaped gates. Inner cortical shell of the same shape, but one-third smaller, four times as large as the lentelliptical medullary shell.

Dimensions.--Length of the medullary shell 0.04, breadth 0.03; length of the inner cortical shell 0.16, breadth 0.12; length of the outer cortical shell 0.24, breadth 0.18.

Habitat.--North Pacific, Station 253, depth 3125 fathoms.

{660}2. Pylozonium octacanthum, n. sp. (Pl. 9, fig. 16).

Outer cortical shell lentelliptical, one and a third times as long as broad, with thorny surface and eight long and thin radial spines arising from the corners of the four elliptical gates, and lying opposite in pairs in two crossed diagonal planes. Inner cortical shell of the same shape but one-fourth smaller, about twice as large as the lentelliptical medullary shell.

Dimensions.--Length of the medullary shell 0.065, breadth 0.045; length of the inner cortical shell 0.18, breadth 0.12; length of the outer cortical shell 0.24, breadth 0.18.

Habitat.--North Pacific, Station 244, depth 2900 fathoms.

Family XXVII. #THOLONIDA#, n. fam. (Pl. 10).

Definition.--#Larcoidea# with regular, completely latticed cortical shell, which is composed of two to six or more hemispherical or cap-shaped domes (vaulted chambers or cupolas). The domes lie opposite in pairs on the poles of the three dimensive axes, are separated by annular constrictions, and surround a simple or Larnacilla-shaped central chamber.

The family #Tholonida# represents a peculiar and very remarkable group of the #Larcoidea#, distinguished from the other groups of this suborder by the characteristic form of the shell, composed of a variable number of hemispherical domes or cupolas. The middle and original part of the shell is constantly formed of an elliptical or subspherical central chamber, which often, but not constantly, contains a small medullary shell. An even number (two, four, six, or more) of domes is attached to the poles of the three dimensive axes of the central chamber; according as only one, or two, or all three axes develop cupolas, we distinguish in this family three different subfamilies (the Amphitholida, Staurotholida, and Cubotholida). The Amphitholida (or Tholonida monaxonia) form cupolas only on the two poles of one single axis, and this axis corresponds to the minor (or transverse) axis of the central chamber, we find here therefore constantly at least two lateral cupolas (Pl. 10, figs. 1-7). The Staurotholida (or Tholonida diaxonia) form cupolas on the poles of two axes perpendicular one to another; these two axes are the major (principal) and the minor (transverse) axis of the central chamber, we find here therefore constantly at least four cupolas crossed in pairs (Pl. 10, figs. 8-11). The Cubotholida (or Tholonida triaxonia) form cupolas on the poles of all three dimensive axes (perpendicular one to another); corresponding to the principal, transverse, and sagittal axes of the lentelliptical central chamber; therefore we find here constantly at least six cupolas, attached in pairs on the six sides of the central chamber (Pl. 10, figs. 12-17).

The number of genera and species in the family #Tholonida# is rather large, but the number of individuals is much smaller than in most of the other SPUMELLARIA, and {661}particularly than in the nearly allied Pylonida; the greater number of the species are very rare. Besides this they seem to be very variable and inclined to produce numerous abnormalities. Very often intermediate forms of transition are to be found between the Tholonida and other #Larcoidea#, particularly the Pylonida and Lithelida. In many species the thick-walled shell is very opaque, and offers great difficulties to the clear study; in the greater number the structure of the shell cannot be understood completely without rolling the shell to the different sides; and the distinction between the Staurotholida and Cubotholida is often very difficult.

The primordial chamber of the Tholonida, or the central chamber in which its growth begins, is either a simple lentelliptical shell (without enclosed medullary shell), like Cenolarcus, or it is a trizonal shell, like Larnacilla, and contains a small concentric medullary shell. But this important inner shell of the central chamber offers peculiar difficulties for study. In many cases (probably in the greater number) there is no doubt the same characteristic trizonal medullary shell, which we found in the Larnacida and Pylonida, and this is our principal argument, if we regard the Tholonida as #Larcoidea#, which are most nearly allied to both these families, and in which the fenestrated open cortical girdles of the Pylonida are replaced by fenestrated closed cupolas or domes; the characteristic "gates" or large fissures in the cortical shell of the former are therefore here perfectly closed by network. The Tholonida agree in this point with the Larnacida, but are distinguished from them by the prominent vaultings of the hemispherical cupolas or domes, which give them a peculiar appearance. Each pair of domes (opposite on both poles of one dimensive axis) corresponds to one single girdle of the Pylonida.

Regarding the absence or presence of a medullary shell in the central chamber, we may divide the Tholonida into two groups, Cenotholida (without medullary shell) and Coccotholida (with medullary shell). The absence of the medullary shell in many Tholonida may be either primary (original) or secondary (by reduction and loss of it). Probably in the larger proportion (if not always?) its absence is the consequence of reduction and loss, and in this case the Cenotholida must be derived phylogenetically from the Coccotholida, but possibly often (or always?) the contrary may also be the case. At present we cannot find certain arguments for one opinion or the other.

The connection between the medullary (internal) and the cortical (external) shell of the central chamber in the Coccotholida is effected by two lateral wings of a latticed transverse girdle; on both sides of the latter remain the four internal open "gates" of the Pylonida and Larnacida. Very often the limiting edges of these four gates are prolonged into eight external radial spines which lie opposite in pairs in two crossed diagonal planes, and correspond to the eight portal-spines of Tetrapyle octacantha. Besides these, we often find four other beams opposite in pairs in the two crossed axes (principal and lateral). Very often also these radial beams (between medullary and {662}cortical shells) are prolonged on the outside into prominent free radial spines. But other spines may also arise from the surface. Very remarkable is the presence of twenty symmetrically disposed radial spines in some forms of Amphitholida (Amphitholus acanthometra and Amphitholonium acanthonium, &c.). It recalls the twenty radial spines of the #Acanthonida#, though the laws of distribution in the two similar cases are quite different.

The cortical shell of the Tholonida remains either simple, or it becomes doubled by formation of an outer veil or envelope. This outer cortical shell or "veil" may either repeat completely the typical form of the inner with its cupolas, or it may form an ellipsoidal envelope without dome-shaped partitions. Its network is either like that of the inner, or it is very delicate and irregular, spider-web like. The connection between the two cortical shells is effected by a variable number of radial beams, often prolonged on the outside into radial spines.

The growth of the Tholonida by apposition of new chambers is very characteristic, constantly pairs of chambers originating at both opposite poles of the three dimensive axes, firstly on the transverse axis, secondly on the principal axis, thirdly on the sagittal axis. It is possible that by repeated apposition of new chambers the Tholonida are transformed into #Discoidea#, but commonly the number of domes is restricted, two in the Amphitholida, four in the Staurotholida, six in the Coccotholida. If new chambers in an irregular manner or in a spiral order be opposed to those first formed pairs of chambers, the Tholonida may be transformed into Soreumida, Streblemida, or Lithelida. The phylogenetic connection between these families is probably very complex and very worthy of further research.

The network of the shell in the Tholonida is sometimes regular, with circular (often hexagonally framed) pores of equal size, sometimes irregular, with roundish pores of unequal size. Commonly the shell is thick and compact; in those genera in which the cortical shell is doubled, the inner is commonly compact, the outer a very delicate veil.

The central capsule of the Tholonida is originally always enclosed by the central chamber, and like this of lentelliptical form, a triaxial ellipsoid. With the apposition of cupolas the growing central capsule may form dome-shaped protuberances which enter into the former. So we may find in the Amphitholida a central capsule with three joints (separated by two annular parallel constrictions), in the Staurotholida a cross-shaped capsule (with four caps around the central lentellipsis), in the Cubotholida a clustered capsule with six caps, surrounding six sides of the cubical central mass. In the Coccotholida (with medullary shell in the central chamber) the latter encloses in the centre the nucleus of the cell. The calymma, or the jelly-veil between the central capsule and the enveloping shell, probably always exhibits annular constrictions, corresponding to those which separate the cupolas of the shell. All these anatomical peculiarities in the Tholonida require a further accurate study.

{663}Synopsis of the Genera of Tholonida.

------------------------------------------------------------------------- I. Subfamily Amphitholida. Cupolas developed only in the direction of one single axis (commonly two cupolas). (Tholonida unidimensiva.) ------------------------------------------------------------------------- {Two simple cupolas { (without veil), 289. Tholartus. Central chamber simple, { without medullary shell. {Two double cupolas { (with veil), 290. Tholodes.

{Two simple cupolas Central chamber { (without veil), 291. Amphitholus. Larnacilla-shaped, with { enclosed medullary shell. {Two double cupolas { (with veil), 292. Amphitholonium. ------------------------------------------------------------------------- II. Subfamily Staurotholida. Cupolas developed in the direction of two axes perpendicular one to another (commonly four cupolas). (Tholonida bidimensiva.) ------------------------------------------------------------------------- {Four simple cupolas { (without veil), 293. Tholostaurus. Central chamber simple, { without medullary shell. {Four double cupolas { (with veil), 294. Tholoma.

{Four simple cupolas Central chamber { (without veil), 295. Staurotholus. Larnacilla-shaped, with { enclosed medullary shell. {Four double cupolas { (with veil), 296. Staurotholonium. ------------------------------------------------------------------------- III. Subfamily Cubotholida. Cupolas developed in the direction of three axes perpendicular one to another (commonly six cupolas). (Tholonida tridimensiva.) ------------------------------------------------------------------------- {Six simple cupolas { (without veil), 297. Tholocubus. Central chamber simple, { without medullary shell. {Six double cupolas { (with veil), 298. Tholonium.

{Six simple cupolas Central chamber { (without veil), 299. Cubotholus. Larnacilla-shaped, with { enclosed medullary shell. {Six double cupolas { (with veil), 300. Cubotholonium.

Subfamily 1. AMPHITHOLIDA, Haeckel.

Definition.--#Tholonida# with monaxial growth; cupolas opposite on the poles of one axis. (Shell commonly three-chambered, with two domes on both sides of the central chamber.)

Genus 289. Tholartus,[328] n. gen.

Definition.--#Tholonida# with simple cortical shell (without external veil); with two hemispherical cupolas, opposite on the poles of one axis; central chamber between them simple (without medullary shell).

{664}The genus Tholartus (Pl. 10, fig. 1) represents the most simple form of all Tholonida, a three-jointed simple cortical shell without medullary shell; two hemispherical cupolas or domes are attached on both lateral sides of a simple triaxial ellipsoidal central chamber, corresponding to the poles of its lateral or transverse axis. Tholartus may be regarded as the common ancestral form of all Tholonida, and may be derived either from the Pylonida Monozonium (by complete lattice-locking of the lateral wings) or from the Ellipsida Cenellipsis (by development of two lateral protuberances on the poles of the transverse axis). But it is also possible that the absence of the medullary shell is produced by reduction, and in this case Tholartus may be descended from Amphitholus.

Subgenus 1. Tholartella, Haeckel.

Definition.--Surface of the shell smooth or rough, without radial spines.

1. Tholartus tricolus, n. sp. (Pl. 10, fig. 1).

Central chamber one and a half times as high and as broad as both cupolas. Surface of the shell rough. Pores regular, circular, without hexagonal frames, three times as broad as the bars; about sixteen on the half meridian of the central chamber (or its vertical diameter).

Dimensions.--Length of the shell (major axis of the central chamber, vertical) 0.1, breadth of the shell (major axis of the whole three-chambered shell, horizontal) 0.13; pores 0.01, bars 0.003.

Habitat.--Pacific, central area, Station 270, depth 2925 fathoms.

2. Tholartus paniscus, n. sp.

Central chamber of the same breadth, but of the double height of both cupolas. Surface of the shell rough. Pores regular, circular, with hexagonal frames, of the same breadth as the bars; eight to ten on the half meridian of the central chamber.

Dimensions.--Length of the shell (major axis of the central chamber, vertical) 0.12, breadth of the shell (major axis of the whole three-chambered shell, horizontal) 0.15; pores and bars 0.008.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

3. Tholartus isocolus, n. sp.

Central chamber of the same breadth and height as both cupolas. Surface of the shell smooth. Pores irregular, roundish, once to three times as broad as the bars; ten to fifteen on the half meridian of the central chamber.

Dimensions.--Length of the shell 0.11, breadth 0.14; pores 0.004 to 0.01, bars 0.003.

Habitat.--Pacific, central area, Station 270, depth 2925 fathoms.

{665}Subgenus 2. Tholartissa, Haeckel.

Definition.--Surface of the shell with radial spines.

4. Tholartus tripanis, n. sp.

Central chamber of the same size as both cupolas. Surface of the shell thorny, everywhere covered with short conical radial spines, about as long as the cupolas. Pores regular or subregular, circular, twice as broad as the bars; eight to ten on the half meridian.

Dimensions.--Length of the shell 0.1, breadth 0.12; pores 0.01, bars 0.005.

Habitat.--South Pacific, Station 295, surface.

5. Tholartus sagitta, n. sp.

Central chamber twice as large as both cupolas. Surface of the shell spiny, with eight to twelve regularly (?) distributed radial spines, radiating from the two constrictions between the three chambers. Spines needle-shaped, very thin and long. Pores subregular or irregular, roundish or circular, about three times as broad as the bars; twelve to sixteen on the half meridian.

Dimensions.--Length of the shell 0.11, breadth 0.15; pores 0.01, bars 0.003.

Habitat.--North Pacific, Station 244, surface.

Genus 290. Tholodes,[329] n. gen.

Definition.--#Tholonida# with double cortical shell (with external veil), with two hemispherical cupolas, opposite on the poles of one axis; central chamber between them simple (without medullary shell).

The genus Tholodes (Pl. 10, fig. 2) differs from Tholartus, its probable ancestral form, only in the duplication of the shell; the outer shell has exactly the same three-jointed form as the inner; both are connected by eight radial beams, lying in two diagonal planes and corresponding to the eight frontal spines of Tetrapyle octacantha. Possibly Tholodes may also be descended from Amphitholonium by loss of the medullary shell. I have observed only one single specimen of this genus.

1. Tholodes cupula, n. sp. (Pl. 10, fig. 2).

Outer shell of the same form and structure as the inner shell. Central chamber larger than both cupolas. Surface a little rough, without radial spines. Distance of both shells equals the height of the outer cupolas. Pores of both shells regular, circular, three times as broad as the {666}bars; six to seven in the semicircle of one inner cupola, ten to twelve in the semicircle of one outer cupola. Both shells are connected by eight radial beams, crossed in two diagonal planes.

Dimensions.--Major axis of the outer shell 0.1, minor 0.065; major axis of the inner shell 0.05, minor 0.04; pores 0.006, bars 0.002.

Habitat.--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Genus 291. Amphitholus,[330] n. gen.

Definition.--#Tholonida# with simple cortical shell (without external veil), with two hemispherical cupolas, opposite on the poles of one axis; central chamber (between them) Larnacilla-shaped, with medullary shell.

The genus Amphitholus is the most simple form of all Coccotholida (or all Tholonida provided with medullary shell). Its simple cortical shell exhibits, like Tholartus, two lateral hemispheric cupolas, attached on both sides of a lentelliptical central chamber (on the poles of its transverse axis). The central chamber has the form of a triaxial ellipsoid, and contains, like Larnacilla, a small medullary shell, connected with it by the wings of a latticed transverse girdle. Amphitholus may be derived either from Tholartus by secondary production of a cortical shell, or (more probably) from Larnacilla by apposition of two lateral dome-shaped protuberances. In the latter case it may be regarded as an Amphipyle, the lateral open wings of which are closed by lattice-work.

Subgenus 1. Amphitholissa, Haeckel.

Definition.--Surface of the shell smooth or rough, without radial spines.

1. Amphitholus artiscus, n. sp. (Pl. 10, fig. 3).

Central chamber of the same height as both cupolas. Surface of the cortical shell rough. Pores regular, circular, with prominent hexagonal frames, twice as broad as the bars; eight to ten in the basal semicircle of one cupola.

Dimensions.--Major axis of the shell 0.16, minor axis 0.1; pores 0.008, bars 0.004.

Habitat.--Pacific, central area, Station 272, depth 2600 fathoms.

2. Amphitholus artidium, n. sp.

Central chamber one-fourth higher than both cupolas. Surface of the cortical shell smooth. Pores irregular, roundish, once to three times as broad as the bars. (Very similar to Tholartus tricolus, Pl. 10, fig. 1, but different by the medullary shell.)

Dimensions.--Major axis of the shell 0.15, minor axis 0.12; pores 0.004 to 0.01, bars 0.003.

Habitat.--North Pacific, Station 241, depth 2300 fathoms.

{667}Subgenus 2. Amphitholura, Haeckel.

Definition.--Surface of the shell with radial spines or thorns.

3. Amphitholus octacanthus, n. sp.

Central chamber about twice as high and broad as both cupolas. From the surface arise, symmetrically distributed, eight stout conical radial spines, lying in two diagonal planes, as prolongations of the eight wing-beams, which connect the Tetrapyle-shaped medullary shell with the two ring-like constrictions of the cortical shell. Pores of the latter regular, circular, twice as broad as the bars; ten to twelve in the basal semicircle of one cupola.

Dimensions.--Major axis of the shell 0.15, minor 0.12; pores 0.01, bars 0.005.

Habitat.--South Atlantic, Station 332, depth 2200 fathoms.

4. Amphitholus dodecanthus, n. sp.

Central chamber a little larger than both cupolas. From the surface arise twelve strong conical radial spines, four on the poles of the major and the minor axis of the shell, lying in the lateral plane; eight others lying in two diagonal planes, as prolongations of the eight wing-beams, which connect the Tetrapyle-shaped medullary shell with the two ring-like constrictions of the cortical shell. Pores of the latter irregular, roundish, twice to four times as broad as the bars; sixteen to eighteen in the basal semicircle of one cupola.

Dimensions.--Major axis of the shell 0.15, minor 0.11; pores 0.004 to 0.008, bars 0.002.

Habitat.--North Pacific, Station 256, surface.

5. Amphitholus acanthometra, n. sp. (Pl. 10, figs. 5, 6).

Central chamber about twice as broad and as high as both cupolas. On the surface quite symmetrically distributed twenty long and strong cylindrical radial spines; eight in the sagittal plane or in the meridian plane of the central chamber (four opposite in pairs in the principal and the sagittal axes, four others in the middle between the principal and the sagittal spines); four in the horizontal transverse plane, on both sides of the poles of the major or lateral axis; and eight in diagonal planes (corresponding to the eight wing-spines of Tetrapyle octacantha). In the centre of the central chamber is a distinct trizonal medullary shell like that of Tetrapyle, with two vertical columella beams. Pores of the cortical shell subregular, circular, with elevated hexagonal frames, about four times as broad as the bars; five to seven in the semicircle of one cupola. (This remarkable species differs from Tholartus vicenus in the possession of a medullary shell, from Amphitholonium acanthometra by the simple cortical shell. Compare these species).

Dimensions.--Major axis of the shell 0.14 to 0.16, minor axis 0.10 to 0.12; pores 0.015, bars 0.004; major axis of the medullary shell 0.04 to 0.05, minor (horizontal) axis 0.02 to 0.03; length of the twenty radial spines 0.18 to 0.24, basal breadth 0.01.

Habitat.--South Pacific, Station 300, depth 1375 fathoms.

{668}6. Amphitholus armatus, n. sp.

Central chamber twice as broad, but of the same height, as the flat vaulted cupolas. Surface armed with thirty to forty very large three-sided prismatic spines, longer than the major axis of the shell. Pores irregular, roundish, twice to five times as broad as the bars; eight to nine on the basal semicircle of one cupola.

Dimensions.--Major axis of the shell 0.15, minor axis 0.1; pores 0.006 to 0.015, bars 0.003; length of the spines 0.2 to 0.25, breadth 0.01.

Habitat.--North Atlantic, Station 353, surface.

7. Amphitholus polyacanthus, n. sp.

Central chamber of the same breadth and height as both cupolas. Surface armed with very numerous (sixty to eighty) strong conical spines, about as long as the minor axis of the shell. Pores subregular, circular, twice as broad as the bars; sixteen to eighteen in the basal semicircle of one cupola.

Dimensions.--Major axis of the shell 0.13, minor 0.08; pores 0.006, bars 0.003; length of the radial spines 0.09, breadth 0.006.

Habitat.--South Atlantic, Station 332, depth 2200 fathoms.

8. Amphitholus panicium, n. sp. (Pl. 10, fig. 4).

Central chamber ellipsoidal, nearly twice as broad, but of the same height, as both cupolas. Whole surface thorny; the largest radial thorns about as long as the medullary shell. Pores irregular, roundish, twice to four times as broad as the bars. On the base of each cupola a circle of ten to twelve larger square pores, separated by radial beams, which are prolonged into stouter free spines. This remarkable formation of the cupolas, very rare in this family, recalls the characteristic formation of the distal chambers of the Panartida and Zygartida (e.g., Pl. 40, figs. 4, 8, &c.), where it is very common.

Dimensions.--Major axis of the shell 0.15, minor 0.1; pores 0.005 to 0.012, bars 0.003; large square pores 0.02; axes of the medullary shell 0.03 and 0.02.

Habitat.--Indian Ocean, Madagascar, Rabbe, surface.

Genus 292. Amphitholonium,[331] n. gen.

Definition.--#Tholonida# with double cortical shell (with external veil), with two hemispherical cupolas, opposite on the poles of one axis; central chamber (between them) Larnacilla-shaped, with medullary shell.

The genus Amphitholonium differs from the nearly allied Amphitholus (probably its ancestral form) only in the duplication of the cortical shell; the outer has the {669}same three-jointed form as the inner, and is connected with it by a variable number of radial beams. From the similar Tholodes it differs in the possession of a medullary shell.

1. Amphitholonium tricolonium, n. sp. (Pl. 10, fig. 7).

Outer cortical shell smooth, of the same three-jointed form as the inner, at an equal distance from it throughout the whole circumference; central chamber higher-vaulted than both cupolas. Network of the outer shell delicate, with subregular, circular pores. Pores of the thick-walled inner shell subregular, circular, with hexagonal frames, three times as broad as the bars; eight to ten in the basal semicircle of one cupola.

Dimensions.--Major axis of the outer cortical shell 0.2, minor axis 0.15; major axis of the inner cortical shell 0.16, minor axis 0.11; pores 0.01, bars 0.0035.

Habitat.--South Pacific, Station 302, depth 1450 fathoms.

2. Amphitholonium octostylium, n. sp.

Outer cortical shell lentelliptical, smooth, not articulated, at a varying distance from the three-jointed inner shell; central chamber of the latter twice as high as both hemispherical cupolas. Network of the outer shell very thin, cob-web like. Pores of the inner shell subregular, roundish, twice as broad as the bars; six to seven in the semicircle of one cupola. Eight thin and long, bristle-shaped, radial spines, opposite in pairs in two crossed diagonal planes.

Dimensions.--Major axis of the outer cortical shell 0.16, minor 0.12; major axis of the inner cortical shell 0.12, minor 0.09; pores 0.01, bars 0.005.

Habitat.--Pacific, central area, Station 273, depth 2350 fathoms.

3. Amphitholonium acanthonium, n. sp.

Outer cortical shell of the same three-jointed form as the inner, at a uniform distance from it; central chamber higher vaulted than both cupolas. Network of the outer shell irregular, delicate, of the inner regular, strong, with circular, hexagonally framed pores, three times as broad as the bars; eight to nine in the semicircle of one cupola. On the surface, quite symmetrically disposed, twenty long and strong, cylindrical, radial spines; eight in the sagittal plane, four in the transverse plane; eight in two diagonal planes between the former and the latter. The remarkable geometric disposition of the twenty spines is in this species quite the same as in Amphitholus acanthometra. It differs from this nearly allied species in the double cortical shell.

Dimensions.--Major axis of the outer cortical shell 0.18, minor 0.14; major axis of the inner cortical shell 0.14, minor 0.1; pores 0.012, bars 0.004.

Habitat.--South Pacific, Station 295, surface.

{670}Subfamily 2. STAUROTHOLIDA, Haeckel.

Definition.--#Tholonida# with diaxial growth; cupolas crossed in pairs, opposite on the poles of two axes, perpendicular one to another. (Shell commonly five-chambered, with four domes, cross-wise surrounding the central chamber.)

Genus 293. Tholostaurus,[332] n. gen.

Definition.--#Tholonida# with simple cortical shell (without external veil), composed of four hemispherical cupolas in cross-form, opposite in pairs on the poles of two axes perpendicular one to another; central chamber simple (without medullary shell).

The genus Tholostaurus is the most simple form of the Staurotholida, or the Tholonida with four crossed hemispherical cupolas, lying on the poles of two axes perpendicular one to another. The central chamber communicates by four wide openings with the four domes, and contains no medullary shell. Tholostaurus may originate either from Tholartus by apposition of two opposite cupolas between the first pair, or from Staurotholus by loss of the medullary shell.

Subgenus 1. Tholostaurantha, Haeckel.

Definition.--Surface of the shell smooth or rough, without radial spines.

1. Tholostaurus quadrigatus, n. sp.

All four cupolas nearly of the same size and form, subregular. Surface smooth, without radial spines. Pores subregular, circular, four times as broad as the bars; eight to ten pores in the basal semicircle of one cupola.

Dimensions.--Diameter of the shell 0.12; pores 0.008, bars 0.002.

Habitat.--Pacific, central area, Station 272, surface.

2. Tholostaurus cruciformis, n. sp.

Two opposite cupolas larger than the two others. Surface rough, without radial spines. Pores regular, circular, hexagonally framed, twice as broad as the bars; twelve to fourteen in the basal semicircle of one cupola.

Dimensions.--Major axis of the shell 0.16, minor axis 0.12; pores 0.006, bars 0.003.

Habitat.--Pacific, central area, Station 265, depth 2900 fathoms.

{671}Subgenus 2. Tholostauroma, Haeckel.

Definition.--Surface of the shell with radial spines or thorns.

3. Tholostaurus tetrabelonis, n. sp.

All four cupolas nearly of the same size and form, subregular. Pores regular, circular, hexagonally framed, twice as broad as the bars; twelve to fourteen in the semicircle of one cupola. Four long and stout conical radial spines, two vertical on the poles of the principal axis, two horizontal on the poles of the transverse axis.

Dimensions.--Major axis of the shell 0.15, minor 0.13; pores 0.006, bars 0.003.

Habitat.--South Pacific, Station 288, surface.

4. Tholostaurus octobelonis, n. sp.

Two opposite cupolas larger than the two others. Pores subregular, circular, three times as broad as the bars; ten to twelve in the semicircle of one cupola. Eight long and thin, needle-shaped, radial spines, in pairs crossed in two diagonal planes.

Dimensions.--Major axis of the shell 0.16, minor 0.12; pores 0.01, bars 0.003.

Habitat.--South Pacific, Station 291, surface.

5. Tholostaurus dodecabelos, n. sp.

Two opposite cupolas larger than the two others. Pores irregular, roundish, twice to three times as broad as the bars; six to eight in the semicircle of one cupola. Twelve thin and long radial spines, four on the poles of the two crossed axes (principal and lateral), eight crossed in two diagonal planes.

Dimensions.--Major axis of the shell 0.14, minor 0.11; pores 0.006 to 0.01, bars 0.003.

Habitat.--North Pacific, Station 244, depth 2900 fathoms.

6. Tholostaurus polybelonis, n. sp.

Two opposite cupolas larger than the two others. Pores circular, hexagonally framed, of the same breadth as the bars; ten to twelve in the semicircle of one cupola. Numerous (twenty to thirty or more) thin, bristle-like, radial spines, about as long as the radius of the shell.

Dimensions.--Major axis of the shell 0.15, minor axis 0.12; pores and bars 0.007.

Habitat.--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

Genus 294. Tholoma,[333] n. gen.

Definition.--#Tholonida# with double cortical shell (with external veil), composed of four hemispherical cupolas in cross-form, opposite in pairs on the poles of two axes perpendicular one to another; central chamber simple (without medullary shell).

{672}The genus Tholoma (Pl. 10, figs. 10, 13) differs from the preceding Tholostaurus (its probable ancestral form) only in the duplication of the shell. The outer (secondary) shell has the same cross-form as the inner (primary) shell. In the two observed species the growth seems to be different, in the first species all four cupolas of each cross being of the same size, form, and age; in the second two opposite cupolas, larger and apparently older than the other two. Tholoma is possibly the offspring of Staurotholonium, from which it may have been produced by loss of the medullary shell.

Subgenus 1. Tholomantha, Haeckel.

Definition.--Surface of the shell smooth, without radial spines.

1. Tholoma quadrigeminum, n. sp. (Pl. 10, fig. 10).

All four chambers in each cortical shell nearly equal, subregular. Surface smooth, without radial spines. Structure of the network in both shells similar. Pores regular, circular, twice as broad as the bars; six to eight in the basal semicircle of one inner, ten to twelve in the semicircle of one outer cupola.

Dimensions.--Diameter of the outer shell 0.14, of the inner 0.09; pores 0.006, bars 0.003.

Habitat.--South Pacific, Station 302, surface.

Subgenus 2. Tholomura, Haeckel.

Definition.--Surface of the shell with radial spines.

2. Tholoma metallasson,[334] n. sp. (Pl. 10, fig. 13).

Two opposite chambers in each cortical shell larger than the two others; the larger chambers of the inner shell corresponding to the smaller chambers of the outer shell. Network in both shells of the same structure, regular, with circular, hexagonally framed pores of the same breadth as the bars; eight to ten in the semicircle of an inner, fourteen to sixteen in the semicircle of an outer cupola. Numerous (twenty to thirty or more) thin, cylindrical, bristle-shaped, long radial spines, symmetrically disposed.

Dimensions.--Major axis of the outer shell 0.26, minor axis 0.2; major axis of the inner shell 0.16, minor axis 0.13; pores and bars 0.006.

Habitat.--Pacific, central area, Station 265, depth 2900 fathoms.

Genus 295. Staurotholus,[335] n. gen.

Definition.--#Tholonida# with simple cortical shell (without external veil), composed of four hemispherical cupolas in cross-form, opposite in pairs on the poles of {673}two axes perpendicular one to another; central chamber Larnacilla-shaped (with enclosed medullary shell).

The genus Staurotholus differs from Tholostaurus in the possession of a medullary shell in the central chamber, and may be derived from this genus by its production. But it may also be derived from Amphitholus by apposition of two secondary opposite cupolas between the two primary cupolas. The symmetrical position of an increasing number of radial spines in the different species is remarkable (resembling Tholostaurus as well as Amphitholus).

Subgenus 1. Staurotholissa, Haeckel.

Definition.--Surface of the shell smooth or rough, without radial spines.

1. Staurotholus quadratus, n. sp.

Surface of the cortical shell smooth. All four cupolas nearly of the same size and form; therefore principal and lateral axes equal. Pores regular, circular, with hexagonal frames, twice as broad as the bars; eight to ten on the basal semicircle of one cupola. Medullary shell square.

Dimensions.--Diameter of the cortical shell 0.15; pores 0.01, bars 0.005.

Habitat.--South Atlantic, Station 323, depth 1900 fathoms.

2. Staurotholus cruciatus, n. sp.

Surface of the cortical shell rough. The two principal cupolas somewhat larger than the two lateral cupolas; therefore the longitudinal axis longer than the transverse. Pores irregular, roundish, twice to three times as broad as the bars; twelve to sixteen in the semicircle of one cupola.

Dimensions.--Major axis of the shell 0.16, minor 0.13; pores 0.005 to 0.009, bars 0.003.

Habitat.--Pacific, central area, Station 266, depth 2750 fathoms.

Subgenus 2. Staurotholura, Haeckel.

Definition.--Surface of the shell with radial spines.

3. Staurotholus tetrastylus, n. sp. (Pl. 10, fig. 8).

The two principal cupolas smaller than the two lateral cupolas. Pores subregular, circular, three times as broad as the bars; six to eight in the semicircle of one cupola. Medullary shell elliptical. On the surface four long cylindrical radial spines; two in the principal and two in the lateral axis.

Dimensions.--Major axis of the cortical shell 0.15, minor 0.12; pores 0.012, bars 0.004.

Habitat.--South Pacific, Station 166, surface.

{674}4. Staurotholus octostylus, n. sp.

The two lateral cupolas larger than the two principal cupolas. Pores subregular, circular, twice as broad as the bars; ten to twelve in the semicircle of one cupola. Medullary shell hexagonal, connected with each ring-like constriction by eight strong cylindrical radial spines (longer than the whole shell), lying in two crossed meridian planes, and corresponding to the eight diagonal wing-spines of Tetrapyle octacantha.

Dimensions.--Major axis of the cortical shell 0.12, minor 0.1; pores 0.008, bars 0.004.

Habitat.--Pacific, central area, Station 274, depth 2750 fathoms.

5. Staurotholus decastylus, n. sp.

The two principal cupolas twice as broad and high as the two lateral cupolas. Pores subregular, circular, four times as broad as the bars; six to eight in the semicircle of one cupola. Ten long and thin radial spines with thickened conical bases, about as long as the major axis of the shell, by inner prolongations connected with the lentelliptical medullary shell; two polar spines in the principal axis, eight wing-spines in two crossed diagonal planes.

Dimensions.--Major axis 0.12, minor 0.1; pores 0.012, bars 0.003.

Habitat.--Western Tropical Pacific; Station 224, depth 1850 fathoms.

6. Staurotholus dodecastylus, n. sp. (Pl. 10, fig. 9).

The two lateral cupolas larger than the two principal cupolas. Pores subregular, circular, three times as broad as the bars; five to seven in the semicircle of one cupola. Twelve strong cylindrical radial spines, four on the poles of the two larger axes (two principal and two lateral), eight wing-spines in two crossed diagonal planes. Medullary shell hexagonal.

Dimensions.--Major (lateral) axis 0.11, minor (principal) 0.09; pores 0.009, bars 0.003.

Habitat.--Tropical Atlantic, Station 348, surface.

7. Staurotholus polystylus, n. sp.

The two principal cupolas larger than the two lateral cupolas. Pores irregular, roundish, twice to three times as broad as the bars; ten to twelve in the semicircle of one cupola. On the surface numerous thin bristle-shaped spines (twenty to thirty or more).

Dimensions.--Major axis 0.14, minor 0.11; pores 0.006 to 0.01, bars 0.003.

Habitat.--North Pacific, Station 231, surface.

Genus 296. Staurotholonium,[336] n. gen.

Definition.--#Tholonida# with double cortical shell (with external veil), composed of four hemispherical cupolas in cross-form, opposite in pairs on the poles of two axes perpendicular one to another; central chamber Larnacilla-shaped (with medullary shell).

{675}The genus Staurotholonium differs from the nearly allied Staurotholus (its probable ancestral form) only in the duplication of the cortical shell. The outer shell commonly repeats the cross-form of the inner, with four corresponding cupolas; but sometimes the four cupolas of the outer shell alternate in size and form with those of the inner, or the outer shell forms a simple lenticular envelope around the inner. From the similar Tholoma, Staurotholonium differs in the possession of a medullary shell in the central chamber.

Subgenus 1. Staurotholodes, Haeckel.

Definition.--Surface of the outer cortical shell smooth or rough, without radial spines.

1. Staurotholonium biquadratum, n. sp.

Outer cortical shell smooth, of the same regular crucial form as the inner, equidistant from it everywhere. Form and structure of both cortical shells nearly the same, but the outer about twice as large as the inner; both connected only by eight diagonal beams. All four cupolas of each cortical shell regular, of the same size. Pores regular, circular, twice as broad as the bars; six to eight in the basal semicircle of each cupola. Medullary shell square. (Similar to Staurotholus quadratus, but differs by the double cortical shell.)

Dimensions.--Diameter of the outer cortical shell 0.16, of the inner 0.08, of the medullary shell 0.04; pores of the inner cortical shell 0.006, bars 0.003.

Habitat.--South Pacific, Station 295, depth 1500 fathoms.

2. Staurotholonium bicruciatum, n. sp.

Outer cortical shell rough, twice as large as the inner, of the same form and structure, at an equal distance from it. In both shells the principal cupolas are larger than the lateral. Pores irregular, roundish, in the outer shell four times, in the inner twice as large as the bars; eight to ten in the basal semicircle of one cupola. (Similar to Staurotholus cruciatus, but differs mainly in the double cortical shell.) Medullary shell lentelliptical.

Dimensions.--Major (longitudinal) axis of the outer cortical shell 0.016, of the inner 0.08; minor (transverse) axis of the former 0.14, of the latter 0.07; medullary shell 0.03 to 0.04.

Habitat.--Pacific, central area, Station 267, depth 2700 fathoms.

3. Staurotholonium alternatum, n. sp.

Outer cortical shell smooth, very different from the inner; in the outer the two principal cupolas are larger than the two lateral; in the inner inversely smaller. Pores subregular, circular, in the outer shell four times, in the inner shell twice as broad as the bars; ten to twelve pores in the basal semicircle of one cupola.

{676}Dimensions.--Major axis (length) of the outer cortical shell 0.15, minor (breadth) 0.13; pores 0.012, bars 0.003; major axis (length) of the inner cortical shell 0.11, minor axis (breadth) 0.09; pores 0.006, bars 0.003.

Habitat.--Indian Ocean, surface, Madagascar, Rabbe.

4. Staurotholonium lenticulare, n. sp.

Outer cortical shell smooth, lenticular, with circular circumference, with very delicate irregular network and small roundish pores. Its distance from the inner much greater in the four diagonal points than in the four polar points. Inner cortical shell regular, cross-like, with four cupolas of similar size and form. Pores subregular, circular, twice as broad as the bars; eight to ten in the basal semicircle of one cupola. Medullary shell lenticular.

Dimensions.--Diameter of the outer cortical shell 0.16, of the inner 0.12; pores of the inner 0.008, bars 0.004.

Habitat.--North Atlantic, Station 353, surface.

Subgenus 2. Staurotholoma, Haeckel.

Definition.--Surface of the outer cortical shell with radial spines or thorns.

5. Staurotholonium octodoratium, n. sp.

Outer cortical shell of the same form and structure as the inner, but twice as large, both principal domes somewhat larger than both lateral. Pores subregular, circular, of the same breadth as the bars; five to six in the semicircle of one inner, eight to ten of one outer cupola. Eight thin and long bristle-like spines, opposite in pairs in two crossed diagonal planes.

Dimensions.--Major axis of the outer cortical shell 0.15, minor 0.12; major axis of the inner cortical shell 0.07, minor 0.06; pores and bars 0.005.

Habitat.--North Pacific, Station 231, surface.

6. Staurotholonium octodoronium, n. sp. (Pl. 10, fig. 11).

Outer cortical shell of the same form as the inner, both little distant; network of the outer irregular and delicate. Pores of the inner regular, circular, twice as broad as the bars; seven to nine in the basal semicircle of one cupola. Both lateral domes larger than the principal. Eight long and thin, cylindrical radial spines opposite in pairs in two crossed diagonal planes.

Dimensions.--Major axis of the outer cortical shell 0.2, minor 0.18; major axis of the inner cortical shell 0.16, minor 0.14; pores 0.008, bars 0.004.

Habitat.--South Pacific, Station 288, surface.

{677}Subfamily 3. CUBOTHOLIDA, Haeckel.

Definition.--#Tholonida# with triaxial growth; cupolas lying in pairs on the six sides of a cubical central chamber, opposite at the poles of three axes perpendicular one to another. (Shell commonly seven-chambered, with six domes surrounding the central chamber.)

Genus 297. Tholocubus,[337] n. gen.

Definition.--#Tholonida# with simple cortical shell (without external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the simple cuboidal central chamber (without medullary shell).

The genus Tholocubus is the most simple form of the Cubotholida, or of the Tholonida with domes situated in three axes perpendicular one to another; six hemispherical cupolas lying on the six sides of a cuboidal central chamber; this latter contains no medullary shell. Tholocubus may be derived phylogenetically either from Tholostaurus by apposition of two opposite domes on the flat sides of the cross-shell, or from Cubotholus by loss of the medullary shell.

Subgenus 1. Tholocubulus, Haeckel.

Definition.--Surface of the shell smooth or rough, without radial spines.

1. Tholocubus tessellatus, n. sp. (Pl. 10, fig. 12).

Surface of the shell smooth, without radial spines. Pores regular, circular, hexagonally framed, twice as broad as the bars; eight to twelve pores on the semicircle of one cupola. Principal cupolas smaller than the lateral, larger than the sagittal cupolas.

Dimensions.--Diameter of the shell 0.15; pores 0.01, bars 0.005.

Habitat.--South Atlantic, Station 332, depth 2200 fathoms.

2. Tholocubus tesserarius, n. sp.

Surface of the shell rough, without radial spines. Pores irregular, roundish, once to three times as broad as the bars; twelve to sixteen pores in the semicircle of one cupola. All six cupolas nearly of the same size.

Dimensions.--Diameter of the shell 0.16; pores 0.004 to 0.008, bars 0.003.

Habitat.--North Atlantic, Station 353, depth 2965 fathoms.

{678}Subgenus 2. Tholocubitus, Haeckel.

Definition.--Surface of the shell with radial spines or thorns.

3. Tholocubus tesseralis, n. sp. (Pl. 10, fig. 16).

Surface of the shell with numerous (eight to sixteen) thin and long, bristle-shaped radial spines (the greater part broken off in the figured specimen); pores subregular, circular, three to four times as broad as the bars; ten to twelve in the semicircle of one cupola.

Dimensions.--Major axis of the shell 0.16, minor axis 0.14; pores 0.01, bars 0.0027.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

Genus 298. Tholonium,[338] n. gen.

Definition.--#Tholonida# with double cortical shell (with external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the simple cuboidal central chamber (without medullary shell).

The genus Tholonium (Pl. 10, fig. 17) differs from the preceding Tholocubus only in the duplication of the cortical shell. The outer (secondary) shell forms either a simple (spheroidal or ellipsoidal) thin veil around the inner (primary) shell, or both shells are of the same form, with six corresponding cupolas. Possibly Tholonium is the offspring of Cubotholonium, having originated by loss of the medullary shell.

Subgenus 1. Tholonetta, Haeckel.

Definition.--Surface of the shell smooth or rough, without radial spines or thorns.

1. Tholonium bicubicum, n. sp.

Outer shell with six hemispherical dome-shaped protuberances, corresponding in those of the inner shell. Both shells connected by numerous radial beams. Surface of the outer shell smooth; its network nearly of the same shape as that of the inner, with subregular, circular pores, twice as broad as the bars; ten to fifteen pores on the semicircle of one cupola.

Dimensions.--Diameter of the outer shell 0.14, of the inner 0.12; pores of the latter 0.006, bars 0.003.

Habitat.--South Atlantic, Station 325, depth 2650 fathoms.

{679}2. Tholonium ellipticum, n. sp.

Outer shell ellipsoidal, without dome-shaped protuberances, with smooth surface, without radial spines; network delicate, with subregular, circular pores. Inner shell with regular, circular, hexagonally framed pores, twice as broad as the bars; ten to twelve pores on the semicircle of one cupola.

Dimensions.--Major axis of the outer shell 0.16, minor axis 0.14; major axis of the inner shell 0.14, minor axis 0.12; pores 0.008, bars 0.004.

Habitat.--Pacific central area, Station 267, depth 2700 fathoms.

3. Tholonium sphæricum, n. sp.

Outer shell spherical, without dome-shaped protuberances, with smooth surface, without radial spines; network very delicate, with very small subregular, circular pores. Inner shell with regular, circular pores of the same breadth as the bars; fourteen to sixteen on the basal semicircle of one cupola.

Dimensions.--Diameter of the spherical outer shell 0.15, inner shell 0.12; pores and bars of the inner shell 0.005.

Habitat.--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

Subgenus 2. Tholonilla, Haeckel.

Definition.--Surface of the outer shell covered with radial spines or thorns.

4. Tholonium hexonium, n. sp. (Pl. 10, fig. 17).

Outer shell ellipsoidal, without dome-shaped protuberances, covered with numerous (thirty to fifty) thin and long, bristle-shaped radial spines; network very delicate, irregular, with roundish pores. Inner shell with six marked hemispherical domes of somewhat different sizes; pores regular, circular, with prominent hexagonal frames, twice as broad as the bars; ten to twelve on the basal semicircle of one cupola.

Dimensions.--Major axis of the outer shell 0.15, minor axis 0.14; major axis of the inner shell 0.13, minor axis 0.12; pores 0.008, bars 0.004.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

5. Tholonium sphæronium, n. sp.

Outer shell very thin walled, spherical, without dome-shaped protuberances, with smooth surface, excepting eight large radial spines, rising from the eight corners of the inner cubical central chamber. Pores of the outer shell very small, subcircular. Inner shell very thick walled, with six marked hemispherical domes; pores subregular, circular, with prominent hexagonal frames, twice as broad as the bars; six to eight on the semicircle of one cupola.

{680}Dimensions.--Diameter of the spherical outer shell 0.15, inner shell 0.11; pores of the inner 0.01, bars 0.005.

Habitat.--Pacific, central area, Station 274, depth 2750 fathoms.

Genus 299. Cubotholus,[339] n. gen.

Definition.--#Tholonida# with simple cortical shell (without external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the cuboidal Larnacilla-shaped central chamber (with medullary shell).

The genus Cubotholus differs from Tholocubus in the possession of a medullary shell in the central chamber, and may be derived from this genus by its production; but it may also be derived from Staurotholus by apposition of two opposite domes on the flat sides of the cross-shell. Sometimes all six domes are of the same size and form, but commonly different in pairs.

Subgenus 1. Cubotholissa, Haeckel.

Definition.--Surface of the shell smooth or rough, without radial spines.

1. Cubotholus regularis, n. sp. (Pl. 10, fig. 14).

On the six sides of the cubical central chamber six hemispherical cupolas of the same size and form. Surface smooth. Pores regular, circular, twice as broad as the bars; eight in the basal semicircle of each cupola. Medullary shell apparently spherical (?), connected with the eight corners of the central chamber by eight radial beams, regularly disposed. (This species is remarkable for the perfect symmetry of the shell, the six sides of which appear to be quite similar. It differs from the similar Tholocubus regularis in the possession of a medullary shell.)

Dimensions.--Diameter of the cortical shell (equal in all three dimensive axes) 0.15; pores 0.01, bars 0.005; diameter of the medullary shell 0.04.

Habitat.--Pacific, central area, Station 273, depth 2350 fathoms.

2. Cubotholus quadraticus, n. sp.

Surface of the shell smooth. Both principal cupolas (on the poles of the longitudinal axis) larger than the four other cupolas, which have the same size and lie cross-wise in the equatorial plane. (Therefore two of the three fundamental axes equal, the third larger.) Pores subregular, circular, three times as broad as the bars; ten to twelve in the semicircle of each cupola-basis.

Dimensions.--Major axis 0.16, minor axis 0.12; pores 0.012, bars 0.004.

Habitat.--Indian Ocean, Zanzibar, Pullen; depth 2200 fathoms.

{681}3. Cubotholus rhombicus, n. sp.

Surface of the shell smooth. Both principal cupolas (on the poles of the longitudinal axis) larger than the two lateral (on the poles of the transverse axis), and these larger than the two sagittal cupolas (on the poles of the sagittal axis). Therefore all three fundamental axes unequal. Pores irregular, roundish, twice to four times as broad as the bars; eight to twelve in the basal semicircle of each cupola. Medullary shell lentelliptical.

Dimensions.--Major (principal) axis 0.16, middle (lateral) axis 0.14, minor (sagittal) axis 0.12; pores 0.006 to 0.012, bars 0.003.

Habitat.--South Atlantic, Station 335, depth 1425 fathoms.

Subgenus 2. Cubotholura, Haeckel.

Definition.--Surface of the shell with radial spines or thorns.

4. Cubotholus octoceras, n. sp.

All six cupolas in pairs of different sizes. Both principal domes larger than the lateral domes, and these larger than the sagittal domes. Pores subregular, circular, twice as broad as the bars; eight to ten in the semicircle of each cupola. From the surface arise (at the intersecting points of every three cupolas) eight strong conical radial spines, about as long as the shell-axis; they lie in two diagonal planes, and are the external free prolongations of eight inner beams (homologous with the eight wing-spines of Tetrapyle octacantha), which connect the lentelliptical medullary shell with the eight corners of the cuboidal central chamber.

Dimensions.--Major axis of the cortical shell 0.15, middle 0.13, minor 0.11; pores 0.008, bars 0.004; diameters of the medullary shell corresponding to 0.05, 0.04, 0.03.

Habitat.--Western Tropical Pacific, Station 224, depth 1850 fathoms.

Genus 300. Cubotholonium,[340] n. gen.

Definition.--#Tholonida# with double (or sometimes triple) cortical shell (with external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the cuboidal Larnacilla-shaped central chamber (with medullary shell).

The genus Cubotholonium differs from the nearly allied Cubotholus (its probable ancestral form) only in duplication of the cortical shell. I have observed only two species of this rare form, both rather different. In the first species the outer cortical shell forms a simple spherical thin veil around the inner, the six cupolas of which are nearly of the same form and size. In the second species each of the domes of the {682}inner cortical shell is protected by an outer larger cupola, and besides this the whole shell is enveloped by a thin ellipsoidal veil (Pl. 10, fig. 15). Therefore this species may be the representative of a peculiar genus, the most highly developed of all Tholonida--Tholothauma.

1. Cubotholonium sphæroides, n. sp.

Outer cortical shell (or veil) spherical, with smooth surface; network very delicate, with very thin bars and very small irregular, roundish pores. Inner cortical shell simple, composed of six hemispherical cupolas, surrounding the six sides of the cubical central chamber, which encloses a spherical medullary shell (one-third as large as itself). Network of the inner cortical shell regular, with circular pores of the same breadth as the bars, twelve to fourteen in the basal semicircle of one cupola.

Dimensions.--Diameter of the spherical outer shell 0.2, of the inner cortical shell 0.15; pores and bars of the latter 0.006.

Habitat.--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

2. Cubotholonium ellipsoides, n. sp. (Pl. 10, fig. 15).

Tholothauma ellipsoides, Haeckel, 1883, MS.

Outer cortical shell (or veil) ellipsoidal, with very thin irregular network and thorny surface. Inner cortical shell double, with six double, flatly vaulted cupolas, surrounding the six sides of the Larnacilla-shaped central chamber; the double domes of each shell are in opposite pairs somewhat larger than the alternating pairs. Pores subregular, circular, about the same breadth as the bars; eight to twelve in the basal semicircle of one cupola. Central chamber with ellipsoidal medullary shell. Radial spines short, very numerous.

Dimensions.--Major axis of the outer cortical shell 0.28, minor 0.24; major axis of the inner cortical shell 0.16, minor axis 0.14; pores and bars 0.006; medullary shell 0.03.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

Family XXVIII. #ZONARIDA#, n. fam. (Pl. 50, figs. 9-12).

Definition.--#Larcoidea# with regular, completely latticed cortical shell, distinguished by two to four or more annular constrictions, which lie (all or partly) in the dimensive planes (sagittal, transverse, or lateral), and by which four to eight or more vaulted cupolas or dome-like chambers become separated. In the centre of this chambered cortical shell lies constantly a trizonal or Larnacilla-shaped medullary shell.

The family #Zonarida# comprises a small number of peculiar #Larcoidea#, resembling the Tholonida in the composition of the polythalamous cortical shell by a number of cupolas or dome-shaped protuberances. But the disposition and origin of these latter {683}are quite different. Whilst in the Tholonida the axes of the domes are dimensive axes, and these are separated by annular constrictions lying in diagonal planes, in the Zonarida we find the contrary; the axes of the domes are here diagonal axes, and these are separated by annular constrictions lying in dimensive planes. However, this definition agrees absolutely only in the four-chambered Zonarium and in the eight-chambered Zonidium, whilst in the six chambered Zoniscus only four domes are disposed according to this law, two others, however, in the same manner as in the Tholonida. Therefore this genus is intermediate between both families.

The Cortical Shell of the Zonarida is in all cases completely latticed and of regular lentelliptical fundamental form, as in the nearly allied Larnacida and Tholonida. The three dimensive axes are constantly of different sizes, each with two equal poles; commonly (as in the human body) the principal or longitudinal axis is the longest, the sagittal (or dorso-ventral) axis the shortest; the transverse (or lateral) axis being intermediate between them. Of the three dimensive planes the lateral plane is the largest (determined by the principal and transverse axes); the smallest is the equatorial plane (crossed by the transverse and sagittal axes); the sagittal plane (determined by the sagittal and principal axes) being intermediate between them.

The annular constrictions of the cortical shell which produce the dome-shaped protuberances are different in number in the three known genera--two, three, or four. To each constriction often (but not always) corresponds an internal latticed septum, which connects the cortical with the medullary shell. The number of the cupolas is always double the number of the annular constrictions by which they are separated, therefore four, six, or eight.

In all known Zonarida the sagittal septum is quite constant, but derived from the original axial rod, which lies in the principal axis. By ramification of this axial beam and reticular connection with the sagittal girdle arises the sagittal septum, which we found first in Octopyle, halving the four gates of Tetrapyle. Whilst this sagittal septum (between right and left halves of the body) is common to all three known genera of this family, the number and shape of the other annular constrictions are different. In Zonarium (Pl. 50, fig. 9) we find only one transverse constriction (in the equatorial plane), in Zoniscus (figs. 10, 11) two parallel transverse constrictions (parallel to the equatorial plane, on both sides of it). Zonidium (fig. 12) is a combination of both foregoing genera; it has three parallel transverse constrictions (one in the equatorial plane, and one on each side of it).

The Latticed Domes (cupolas or chambers) of the cortical shell exhibit correspondingly a different number and disposition in the three known genera. In Zonarium are found only four crossed chambers, separated by the sagittal and transverse septa; the axes of the four crossed domes are diagonal axes, whilst in the similar Staurotholus they are dimensive axes (principal and transverse axes). In Zonidium we find eight domes, each cupola of Zonarium being halved by a diagonal septum. Zoniscus is intermediate {684}between the two foregoing genera, and has six cupolas, three on each side of the sagittal septum.

The inner communication of the cupolas or chambers is more or less free, the lattice-work of the separating septa between them commonly remaining more or less imperfect, or represented only by some isolated beams or meshes. The outer network of the cupolas is commonly irregular (as in the majority of #Larcoidea#), but sometimes distinguished by a small number of regularly disposed larger apertures (similar to the "gates" of the Pylonida). From the surface radial spines often arise in characteristic number and symmetrical disposition, commonly as prolongations of the septal axes or of the constricted edges.

The Medullary Shell in all Zonarida is a true trizonal or Larnacilla-shaped lattice-shell (compare above, p. 600); its perimeter (or the first lateral girdle) is sometimes more elliptical, at other times more hexagonal; the hexagon is amphithect; both its lateral sides are often concave and commonly longer than the four other sides.

The Central Capsule in all Zonarida is in a strict geometrical sense a true lentellipsis (compare above, p. 599); its principal axis is commonly one and a third to one and a half times as great as the transverse axis, and twice to three times as great as the sagittal axis. The lentelliptical central capsule encloses the trizonal medullary shell, whilst it is externally enveloped by the chambered cortical shell.

Synopsis of the Genera of Zonarida.

Two annular constrictions and four cupolas, 301. Zonarium.

Three annular constrictions and six cupolas, 302. Zoniscus.

Four annular constrictions and eight cupolas, 303. Zonidium.

Genus 301. Zonarium,[341] n. gen.

Definition.--#Zonarida# with four dome-shaped chambers of the cortical shell, separated by two annular constrictions (one sagittal and one transverse).

The genus Zonarium is the most simple form of the Zonarida, and differs from the nearly allied Larnacalpis by two ring-like constrictions, which are crossed at right angles, one in the sagittal (or median) plane, and one in the transverse (or equatorial) plane. By these two annular constrictions four egg-shaped or kidney-shaped chambers become imperfectly separated, which correspond to the quadrants of the lateral plane. The first cause of the marked constrictions may be the formation of the latticed sagittal septum, which is found first in Octopyle, as halving the four gates of {685}Tetrapyle. Between this septum and the constricted narrow transverse girdle the cortical shell grows out in the form of four vaulted cupolas; every two opposite domes are congruent, two neighbouring are symmetrically equal.

1. Zonarium quadrigatum, n. sp.

Cortical shell quadrangular, one and a half times as long as broad, with four rounded corners. Surface thorny, with numerous short radial spines. Sagittal constriction twice as long as the hexagonal medullary shell. Four cupolas kidney-shaped.

Dimensions.--Length of the cortical shell 0.16, breadth 0.11; length of the medullary shell 0.06, breadth 0.04.

Habitat.--Pacific, central area, Station 272, depth 2600 fathoms.

2. Zonarium quadrispinum, n. sp.

Cortical shell quadrangular, nearly rectangular, about twice as long as broad, with four corners, from which arise four strong, three-sided pyramidal, radial spines (crossed in two diagonals of the lateral plane). Surface thorny, only smooth in the transverse constriction. Sagittal constriction three times as long as the lentelliptical medullary shell. Four cupolas elliptical or nearly quadrangular.

Dimensions.--Length of the cortical shell 0.22, breadth 0.1; length of the medullary shell 0.07, breadth 0.05.

Habitat.--Pacific, central area, Station 274, depth 2750 fathoms.

3. Zonarium octangulum, n. sp. (Pl. 50, fig. 9).

Cortical shell octangular, one and a fourth times as long as broad, with eight strong conical spines on the eight corners; these are separated by four deep constrictions on the poles of the principal and transverse axes, and by four truncated planes on the poles of the crossed diagonal axes between the former. Sagittal constriction twice as long as the hexagonal medullary shell. Four cupolas kidney-shaped or nearly pentagonal.

Dimensions.--Length of the cortical shell 0.15, breadth 0.12; length of the medullary shell 0.07, breadth 0.04.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

4. Zonarium tetratholium, n. sp.

Cortical shell quadrangular, with four rounded corners. Surface thorny, with sixteen stronger radial spines; eight of these lie in the lateral plane, in the same symmetrical disposition as in the foregoing species; eight others lie on both sides of the lateral plane, opposite in pairs in two crossed diagonal planes, in the same symmetrical disposition as in Tetrapyle octacantha. Sagittal {686}constriction three times as long as the lentelliptical medullary shell. Four cupolas obliquely elliptical.

Dimensions.--Length of the cortical shell 0.16, breadth 0.12; length of the medullary shell 0.04, breadth 0.03.

Habitat.--North Pacific, Station 241, depth 2300 fathoms.

Genus 302. Zoniscus,[342] n. gen.

Definition.--#Zonarida# with six dome-shaped chambers of the cortical shell, separated by three annular constrictions (one sagittal and two transverse, parallel to the equatorial plane).

The genus Zoniscus differs from Zonarium as well as from Zonidium by the development of the transverse girdle, which is not constricted, but on the contrary prominently vaulted in the equatorial plane. Therefore both wings of the transverse girdle form here two opposite lateral or "equatorial cupolas," as in Amphitholus. These are separated from four other domes (the "corner cupolas") by two transverse annular constrictions, which correspond to the free edges of the original transverse girdle. The corner domes of each pair are separated from each other by the sagittal septum.

1. Zoniscus rectangulus, n. sp.

Cortical shell nearly rectangular, with rounded corners, nearly one and a half times as long as broad. Surface thorny, without larger radial spines. Sagittal constriction scarcely half as long as the hexagonal medullary shell. Both equatorial cupolas (or wings of the transverse girdle) scarcely half as large as the four corner cupolas.

Dimensions.--Length of the cortical shell 0.15, breadth 0.11; length of the medullary shell 0.07, breadth 0.045.

Habitat.--North Pacific, Station 253, depth 3125 fathoms.

2. Zoniscus hexathalamus, n. sp.

Cortical shell nearly elliptical, one and a third times as long as broad. Surface nearly smooth, without radial spines. Sagittal constriction three times as long as the lentelliptical medullary shell. Both equatorial cupolas about as large as the four corner cupolas.

Dimensions.--Length of the cortical shell 0.12, breadth 0.09; length of the medullary shell 0.035, breadth 0.025.

Habitat.--North Pacific, Station 244, depth 2900 fathoms.

{687}3. Zoniscus tetracanthus, n. sp. (Pl. 50, fig. 10).

Cortical shell nearly quadrangular, one and a half times as long as broad, with four prominent corners, from which arise in the lateral plane four strong, three-sided pyramidal radial spines (opposite in pairs in two crossed diagonal axes). Surface thorny, with exception of the concave lateral sides. Sagittal constriction two and a half times as long as the hexagonal medullary shell. Both equatorial cupolas scarcely half as large as the four corner cupolas.

Dimensions.--Length of the cortical shell 0.18, breadth 0.12; length of the medullary shell 0.07, breadth 0.04.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

4. Zoniscus octacanthus, n. sp.

Cortical shell nearly four-sided, prismatic, one and a third times as long as broad, with spiny surface. Eight longer thin radial spines opposite in pairs in two crossed diagonal planes (as in Tetrapyle octacantha). Sagittal constriction two and a half times as long as the hexagonal medullary shell. Both equatorial cupolas somewhat larger than the four corner cupolas.

Dimensions.--Length of the cortical shell 0.16, breadth 0.12; length of the medullary shell 0.055, breadth 0.04.

Habitat.--Pacific, central area, Station 263, depth 2650 fathoms.

5. Zoniscus hexatholius, n. sp. (Pl. 50, fig. 11).

Cortical shell nearly rectangular, with four rounded corners and deep sagittal constriction, one and a fourth times as long as broad with thorny surface. Twelve longer edged radial spines; eight opposite in pairs in two crossed diagonal planes (as in the foregoing species), four others in the lateral plane, opposite in pairs on both sides of the sagittal constriction, which is scarcely twice as long as the hexagonal, in the equatorial plane constricted medullary shell. Both equatorial cupolas nearly of the same size as the four corner cupolas.

Dimensions.--Length of the cortical shell 0.16, breadth 0.13; length of the medullary shell 0.07, breadth 0.04.

Habitat.--South Pacific, Station 300, depth 1375 fathoms.

Genus 303. Zonidium,[343] n. gen.

Definition.--#Zonarida# with eight dome-shaped chambers of the cortical shell, separated by four annular constrictions (one sagittal, one transverse, and two others parallel to the latter).

The genus Zonidium must be regarded as a Zonarium, in which the four cupolas (in the quadrants of the lateral plane) are halved by diagonal beams or latticed septa, {688}lying opposite in pairs in two crossed diagonal planes. Therefore the number of the septa (four) and the domes (eight) is here doubled. Among the eight cupolas we distinguish four median (on both sides of the sagittal plane) and four lateral (on both sides of the equatorial plane); both groups are of different size and form. Probably Zonidium is derived from Zonarium by lattice-connection between the eight diagonal wing-spines, which in both species of this genus are present, the same as in Tetrapyle octacantha.

1. Zonidium octostylium, n. sp.

Cortical shell nearly quadrangular, with rounded corners and thorny surface. Eight long and thin radial spines on both sides of the lateral plane opposite in pairs and lying in two crossed diagonal planes (as in Tetrapyle octacantha). Sagittal constriction three times as long as the lentelliptical medullary shell. Four medial cupolas (on both sides of the sagittal plane) somewhat larger than the four lateral cupolas (on both sides of the equatorial plane).

Dimensions.--Length of the cortical shell 0.15, breadth 0.12; length of the medullary shell 0.05, breadth 0.03.

Habitat.--Indian Ocean, Madagascar, Rabbe, surface.

2. Zonidium octotholium, n. sp. (Pl. 50, fig. 12).

Cortical shell nearly octangular, with spiny surface; twenty long and stout radial spines between numerous smaller spines; eight wing-spines opposite in pairs in two crossed diagonal planes (as in the preceding species); twelve other strong spines in the lateral plane (four longer opposite in pairs on the poles of the principal and transverse axes, eight others smaller, alternating between these and the diagonal spines). Sagittal constriction twice as long as the hexagonal medullary shell. Four median cupolas somewhat smaller than the four lateral cupolas.

Dimensions.--Length of the cortical shell 0.18, breadth 0.15; length of the medullary shell 0.07, breadth 0.05.

Habitat.--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

Family XXIX. #LITHELIDA#, Haeckel (Pl. 49, figs. 1-7).

Lithelida, Haeckel, 1862, Monogr. d. Radiol., p. 515.

Definition.--#Larcoidea# with symmetrical spiral shell, divided by the spiral plane into two symmetrical halves; all windings of the spiral lie in this plane. Primordial chamber either simple or Larnacilla-shaped.

The family #Lithelida# comprises all those #Larcoidea# in which the growth of the latticed shell is spirally winding in one plane, Nautilus-like. They agree in the spiral growth with the following family. But in the Streblonida the spiral is screw-shaped, {689}ascending (like Helix). Therefore in these latter the geometrical fundamental form of the shell is asymmetrical or "dysdipleural," whereas in the Lithelida bilateral-symmetrical or "eudipleural." The lentelliptical or nearly spherical shell may be divided by a median section into two symmetrical halves; the right half is the mirror image of the left half.

When in 1862 I founded the family Lithelida in my Monograph (p. 515), I knew only one genus, Lithelius, with two species. The rich material of the Challenger collection contains a great number of similar spirally constructed #Larcoidea#, so that at the present time we may distinguish at least six genera. These belong to two different subfamilies, which may possibly be afterwards better separated as families. The first subfamily, Spiremida, possess a simple, spherical or subspherical, medullary shell; the second subfamily, Larcospirida, possess a trizonal or Larnacilla-shaped medullary shell. No doubt these latter must be derived from Pylonida, as we observe all stages of development starting from a simple Trizonium; but perhaps also the Spiremida have the same origin, their simple, spherical or subspherical, medullary shell being derived from a trizonal or Larnacilla-shaped medullary shell by reduction.

The general appearance in both subfamilies of the Lithelida is quite the same, and it requires a careful study of the medullary shell to distinguish certainly the Spiremida from the Larcospirida. This distinction is often not easy, particularly in the larger forms; the shell is often very opaque and difficult to understand. Only in one position, if the spiral axis be parallel to the axis of the eye of the observer, and the spiral plane be therefore fully seen in the optical plane of the microscope, the spiral line (or the axial section of the latticed spiral lamella) is distinctly observed; in all other positions the figure of the spiral is more or less indistinct, and the whole microscopical image often quite intricate and confused. The sufficient study of this family requires therefore the contemplation of the shell from different sides, and is the more difficult, as the variability of the Lithelida--as of the Pylonida--is extraordinarily great.

The description which I gave of Lithelius (1862) in my Monograph is in some points erroneous, and was afterwards (1879) corrected by R. Hertwig, who explained particularly the near relation of it to Tetrapyle. Indeed the intermediate forms between the Lithelida and the Pylonida are so numerous and so evident in all stages of development, that the derivation of the former (at least of the Larcospirida) from the latter is quite clear. The analogy between the structure of the Lithelida and the calcareous (foraminiferous) Alveolinida is not so complete as I supposed it to be in my Monograph (1862); particularly the formation of the small chambers between the turnings of the spiral lamella is much more complete in the Alveolinida than in the Lithelida.

The cortical shell of all Lithelida has the same geometrical fundamental form as Nautilus or as the nautiloid Polythalamia (Polystomella, Nummulites, &c.); therefore the shell is dipleural, being divided by the median plane into two symmetrical lateral halves. {690}Since the spiral line lies in the median plane, we will call it the spiral plane; it separates the right half from the left. The axis of the body, around which the spiral turns (without touching it), is the spiral axis. The latticed part of the cortical shell, which turns around them, is the spiral lamella. Only in one genus of our family, viz., Tholospira, are the spiral axis, the lateral axis, the spiral plane, and the sagittal plane quite as in Nautilus. In all other genera this disposition is different or is uncertain. This depends on the different part of the cortical shell, from which the spiral growth begins. In this respect we can distinguish four different modes.

In the Larcospirida (or the Lithelida with Larnacilla-shaped medullary shell) the spiral growth exhibits four quite different forms. It begins here with Larcospira, in which already the first cortical girdle of the Diplozonaria determines the spiral growth; one wing of this girdle, the transverse girdle of Amphipyle, grows more swiftly than the other, overgrows it, and thus turns around the principal axis. In Pylospira the first or transverse girdle is already perfectly formed (as in Amphipyle), and the spiral growth is introduced by the second or lateral girdle of Tetrapyle; one wing of it (the right or the left) grows more swiftly than the other, overgrows it, and thus turns around the sagittal axis. In Tholospira also the second girdle is complete, and the spiral growth begins from the third or sagittal girdle. One of its wings grows more swiftly than the other, overgrows it, and thus turns around the transverse axis. Consequently we see that each of the three dimensive planes of the lentelliptical Larcoid-body may be the spiral plane: in Larcospira the transverse plane, in Pylospira the lateral plane, in Tholospira the sagittal plane. Correspondingly the spiral axis in the first genus is the principal, in the second the sagittal, in the third the transverse axis of the central Larnacilla-shell. Therefore in these three genera the spiral plane is the plane of the latticed girdle, which determines the spiral growth, one of both its wings overgrowing the other.

In each of the three above mentioned genera the spiral may be simple or double; it remains simple if only one of both wings of the turning girdle overgrow the other, and this latter remain a simple half girdle (or tube-like wing). Whereas the spiral becomes double if the second wing of the girdle afterwards follow the example of the first wing and now turn around it in the same direction. As this happens in all three genera, we can subdivide them into six subgenera.

A quite peculiar form of spiral growth is produced in Spironium, in which the direction of growth in both lateral wings of the transverse girdle is inverse from the beginning. The left wing grows against the posterior, the right wing against the anterior pole of the principal axis, turning around it in crossed, eight-like spirals. The whole shell afterwards assumes a lentelliptical form.

Commonly between the embracing spiral turnings or convolutions a great number of radial beams is developed, irregularly disposed and often branching; they support the {691}thin spiral lamellæ and give to the whole shell more solidity. Often these beams form imperfect radial septa, by which the spiral cavity of the turnings is divided into a variable number of chambers. But these chambers never become so regular and perfect as in the analogous nautiloid Polythalamia.

In many Lithelida the growth of the shell reaches a certain limit, concluding with the formation of a superficial latticed lamella of lentelliptical or nearly spherical form. In many other forms of the family this seems not to be the case; but these may possibly be younger forms, afterwards reaching the same limit.

The network of the shell in the Lithelida is commonly quite irregular, and so variable that its special conformation has usually no value in the determination of the species. The surface of the shell is often covered with radial spines, which are sometimes arborescent.

The central capsule seems always to preserve the same lentelliptical form (or triaxial ellipsoid) as in all other #Larcoidea#. With the increase of growth it encloses successively a larger part of the spiral cortical shell, but on the outside is constantly protected by the last turnings of the spiral, or by the lattice-lamella of the surface.

Synopsis of the Genera of Lithelida.

------------------------------------------------------------------------- I. Subfamily Spiremida. Central medullary shell simple, spherical or lentelliptical. ------------------------------------------------------------------------- Surface of the cortical shell smooth or thorny, without radial spines, 304. Spirema.

Surface of the cortical shell covered with numerous simple or branched radial spines, 305. Lithelius. ------------------------------------------------------------------------- II. Subfamily Larcospirida. Central medullary shell double, trizonal or Larnacilla-shaped. ------------------------------------------------------------------------- The transverse girdle turns around the principal axis, 306. Larcospira.

The lateral girdle turns around the sagittal axis, 307. Pylospira.

The sagittal girdle turns around the transverse axis, 308. Tholospira.

Both wings of the transverse girdle turn around the principal axis in an opposite diagonal direction, 309. Spironium.

Subfamily 1. SPIREMIDA, Haeckel, 1881, Prodromus, p. 464.

Definition.--#Lithelida# with simple, spherical or subspherical, medullary shell.

Genus 304. Spirema,[344] Haeckel, 1881, Prodromus, p. 464.

Definition.--#Lithelida# with simple, spherical or subspherical, medullary shell, and lentelliptical or subspherical, spirally constructed cortical shell; surface smooth or thorny, without radial spines.

{692}The genus Spirema begins the series of the Spiremida, or of those Lithelida in which the medullary shell presents a simple latticed sphere or ellipsoid, never composed of a double, trizonal or Larnacilla-shaped shell. In the present state of our knowledge we cannot say whether this simple medullary shell be a primary formation, or effected by secondary means, by reduction of a double Larnacilla-shaped medullary shell, which is constantly found in the Larcospirida. The species of this genus (as of all Lithelida) are difficult to distinguish, are transformistic, and incline very much to variations and abnormalities. The spiral may be simple or double.

Subgenus 1. Spiremarium, Haeckel.

Definition.--Spiral convolutions of the cortical shell simple.

1. Spirema lentellipsis, n. sp.

Cortical shell lentelliptical, with smooth surface; proportion of its three dimensive axes = 4 : 5 : 6. In the median plane are visible four perfect turnings of the simple spiral, the breadth of which gradually increases towards the third convolution, finally decreasing; the broadest (third) turning three times as broad as the simple spherical medullary shell.

Dimensions.--Length of the lentelliptical cortical shell 0.18, breadth 0.15, height 0.12; diameter of the spherical medullary shell 0.02.

Habitat.--North Atlantic, Station 353, surface.

2. Spirema melonia, n. sp. (Pl. 49, fig. 1).

Cortical shell nearly spherical, with smooth surface; proportion of its three dimensive axes = 1.4 : 1.5 : 1.6. In the median plane are visible three perfect turnings of the simple spiral, all of the same breadth as the simple spherical medullary shell; the breadth of each convolution somewhat greater at the poles of the principal than at the poles of the sagittal axis.

Dimensions.--Length of the shell 0.16, breadth 0.15, height 0.14; medullary shell 0.018.

Habitat.--Pacific, central area, Station 271, surface.

3. Spirema flustrella, Haeckel.

Flustrella haliomma, Ehrenberg (1861), Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, p. 293, Taf. ii. fig. 6.

Cortical shell egg-shaped, with thorny surface; proportion of its three axes = 4 : 5 : 6. In the median plane are visible three perfect turnings of the simple spiral, the first and second of about the same breadth as the simple spherical medullary shell, the third suddenly increasing, and finally three to four times as broad. Network of the surface irregular, with roundish pores.

Dimensions.--Length of the shell 0.2, breadth 0.17, height 0.14; medullary shell 0.013.

Habitat.--North Atlantic, Greenland, 1000 fathoms, Ehrenberg; Færöe Channel, John Murray.

{693}Subgenus 2. Spiremidium, Haeckel.

Definition.--Spiral convolutions of the cortical shell double.

4. Spirema diplospira, n. sp.

Cortical shell lentelliptical, with smooth surface; proportion of its three dimensive axes = 6 : 7 : 8. In the median plane are visible three perfect turnings of a double spiral, the breadth of which gradually increases; the broadest (third) convolution three times as broad as the simple lentelliptical medullary shell.

Dimensions.--Length of the shell 0.24, breadth 0.21, height 0.18; medullary shell 0.02.

Habitat.--Tropical Pacific, Philippines, Station 200, depth 250 fathoms.

5. Spirema subglobosum, n. sp.

Cortical shell nearly spherical, with thorny surface; proportion of its three axes = 2 : 2.1 : 2.2. In the median plane are visible two perfect turnings of a double spiral, the breadth of which in the second convolution is four times as great as that of the first convolution and the simple spherical medullary shell.

Dimensions.--Length of the shell 0.22, breadth 0.21, height 0.2; medullary shell 0.02.

Habitat.--Tropical Atlantic, off Sierra Leone, Station 348, depth (2450) fathoms.

Genus 305. Lithelius,[345] Haeckel, 1862, Monogr. d. Radiol., p. 519.

Definition.--#Lithelida# with simple, spherical or subspherical, medullary shell, and lentelliptical or subspherical, spirally constructed cortical shell; surface covered with numerous, simple or branched, radial spines.

The genus Lithelius, founded by me in 1862, and represented by two Mediterranean species, was at that time the only known form of this family, which now contains six genera and twenty-seven species. It differs from the foregoing Spirema in the possession of numerous radial spines on the surface. These may be either simple or branched. The spiral may be simple or double, and according to this latter modification we distinguish two different subgenera.

Subgenus 1. Lithospira, Haeckel.

Definition.--Spiral convolutions of the cortical shell simple.

1. Lithelius spiralis, Haeckel.

Lithelius spiralis, Haeckel, 1862, Monogr. d. Radiol., p. 519, Taf. xxvii. figs. 6, 7.

Cortical shell lentelliptical, one and a third times as long as broad, covered with very numerous (one hundred to one hundred and fifty or more) simple, bristle-shaped radial spines, about as long {694}as the shell. Spiral turnings simple, all nearly of the same breadth and scarcely broader than the simple spherical medullary shell.

Dimensions.--Length of the cortical shell (with six spiral convolutions) 0.15, breadth 0.13; diameter of the medullary shell 0.012.

Habitat.--Mediterranean, Messina, Haeckel, surface; Atlantic, Stations 348 to 353, surface.

2. Lithelius primordialis, R. Hertwig.

Lithelius primordialis, R. Hertwig, 1879, Organism. d. Radiol., p. 54, Taf. vi. figs. 4, 4_a_.

Cortical shell subspherical, covered with numerous simple, bristle-shaped radial spines, longer than the shell. Spiral turnings simple, with gradually increasing breadth, so that the beginning of the third spiral is twice as broad as the first and as the simple spherical medullary shell.

Dimensions.--Diameter of the cortical shell (with two spiral convolutions) 0.12; diameter of the medullary shell 0.02.

Habitat.--Mediterranean, Messina, R. Hertwig, surface.

3. Lithelius alveolina, Haeckel, 1862.

Lithelius alveolina, Haeckel, 1862, Monogr. d. Radiol., p. 520, Taf. xxvii. figs. 8, 9.

Cortical shell spherical, covered with simple, very numerous (two hundred to three hundred or more), short, bristle-shaped radial spines, scarcely half as long as the radius of the shell. Spiral turnings simple, with gradually increasing breadth, so that the beginning of the third spiral is three times as broad as the first and as the simple spherical medullary shell.

Dimensions.--Diameter of the cortical shell (with four spiral convolutions) 0.2; diameter of the medullary shell 0.01.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific, on many Stations, surface.

4. Lithelius capreolus, n. sp.

Cortical shell lentelliptical, one and a fourth times as long as broad, covered with numerous (eighty to one hundred and twenty or more) short, branched radial spines, about half as long as the radius of the shell; each spine once or twice dichotomous, with curved divergent branches. Spiral turnings simple, with gradually increasing breadth, so that the beginning of the third spiral is twice as broad as the first, and as the simple spherical medullary shell.

Dimensions.--Length of the cortical shell (with four spiral convolutions) 0.18, breadth 0.14; diameter of the medullary shell 0.015.

Habitat.--Pacific, central area, Station 274, surface.

Subgenus 2. Drymospira, Haeckel, 1881, Prodromus, p. 464.

Definition.--Spiral convolutions of the cortical shell double.

{695}5. Lithelius solaris, n. sp. (Pl. 49, fig. 2).

Cortical shell spherical, covered with simple, very numerous (two hundred to three hundred) bristle-shaped radial spines, longer than the diameter of the shell. Spiral turnings double, both of the same breadth, gradually increasing with the growth of the shell and several times surpassing the diameter of the simple spherical medullary shell. (Pl. 49, fig. 2, exhibits only the first convolutions in the centre of the shell.)

Dimensions.--Diameter of the cortical shell (with four spiral convolutions) 0.18; diameter of the medullary shell 0.02.

Habitat.--Pacific, central area, Stations 266 to 272, surface and in various depths.

6. Lithelius arborescens, n. sp.

Cortical shell lentelliptical, one and a half times as long as broad, covered with numerous (fifty to eighty or more) branched radial spines, about as long as the greatest diameter of the shell; each spine with two to four lateral branches, which are again branched or dichotomous. Spiral turnings double, both of little different breadth, which increases considerably with the growth of the shell, so that the third turn is four times as broad as the simple spherical medullary shell.

Dimensions.--Length of the cortical shell (with three spiral convolutions) 0.18, breadth 0.12; diameter of the medullary shell 0.01.

Habitat.--North Atlantic, Færöe Channel, surface, John Murray.

Subfamily 2. LARCOSPIRIDA, Haeckel.

Definition.--#Lithelida# with double, trizonal, or Larnacilla-shaped medullary shell.

Genus 306. Larcospira,[346] n. gen.

Definition.--#Lithelida# with double, trizonal, or Larnacilla-shaped medullary shell; cortical shell subspherical or lentelliptical, constructed of a simple or double spiral of the transverse girdle (or primary cortical girdle); the spiral lamella revolving around the principal axis.

The genus Larcospira begins the interesting series of the Larcospirida, or of those Lithelida in which the medullary shell is formed by a trizonal or Larnacilla-shaped lattice-shell, and the cortical shell by spiral turnings of one of the three girdles, which compose the cortical shell of the Pylonida. In Larcospira, as the oldest and most simple form of Larcospirida, the spiral is formed by the transverse girdle, or the first girdle of the Diplozonaria, the only cortical girdle of Amphipyle. If in this genus one of both wings of the transverse girdle grow stronger than the other and overgrow the latter, turning {696}around the principal axis, we reach the characteristic form of Larcospirema, the first subgenus of Larcospira; but if afterwards the second wing follow the example of the first, and overgrow it from the other side, we reach the typical form of the second subgenus, Larcospironium. In this latter subgenus the spiral becomes double, whilst in the former it remains simple.

Subgenus 1. Larcospirema, Haeckel.

Definition.--Spiral convolutions or turns of the cortical shell simple; only one single wing of the transverse girdle turning around the principal axis.

1. Larcospira lentelliptica, n. sp.

Cortical shell with smooth surface, four times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a half times as long as broad, without constrictions. One lateral wing of the transverse girdle is more strongly developed and turns around the other in two to three simple spiral turns.

Dimensions.--Length of the cortical shell 0.2, breadth 0.16; length of the medullary shell 0.05, breadth 0.04.

Habitat.--Pacific, central area, Station 265, depth 2900 fathoms.

2. Larcospira quadrangula, n. sp. (Pl. 49, fig. 3).

Cortical shell with thorny surface, three times as long as the lentelliptical medullary shell. Perimeter of the lateral plane nearly quadrangular, with four rounded corners (on the poles of two crossed diagonal axes), one and a third times as long as broad, with one sagittal constriction at the poles of the principal axis. One lateral wing of the transverse girdle turns around the other in one and a half to two simple spiral turns.

Dimensions.--Length of the cortical shell 0.18, breadth 0.14; length of the medullary shell 0.06, breadth 0.04.

Habitat.--Pacific, central area, Station 274, depth 2750 fathoms.

3. Larcospira sexangula, n. sp.

Cortical shell with spiny surface, four times as long as the hexagonal medullary shell. Perimeter of the lateral plane nearly hexagonal, one and a half times as long as broad, with six rounded corners (two on the poles of the principal axis, four on the poles of two crossed diagonal axes), with three slight ring-like constrictions. One lateral wing of the transverse girdle turns around the other in two to two and a half simple spiral turns.

Dimensions.--Length of the cortical shell 0.24, breadth 0.16; length of the medullary shell 0.06, breadth 0.04.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

{697}Subgenus 2. Larcospironium, Haeckel.

Definition.--Spiral convolutions or turns of the cortical shell double; both wings of the transverse girdle turning around the principal axis.

4. Larcospira oliva, n. sp.

Cortical shell with smooth surface, six times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a fourth times as long as broad, without constrictions. Both lateral wings of the transverse girdle turn round one another and form one and a half to two double spiral turns.

Dimensions.--Length of the cortical shell 0.25, breadth 0.2; length of the medullary shell 0.04, breadth 0.035.

Habitat.--Antarctic Ocean, Station 157, depth 1950 fathoms.

Genus 307. Pylospira,[347] n. gen.

Definition.--#Lithelida# with double, trizonal or Larnacilla-shaped medullary shell; cortical shell subspherical or lentelliptical, constructed of a single or double spiral of the lateral girdle (or second cortical girdle); the spiral lamella revolving round the sagittal axis.

The genus Pylospira follows after Larcospira as the second genus of Larcospirida; but in this latter the spiral of the cortical shell is formed by the transverse girdle (or the first lattice-girdle of the Diplozonaria), whilst in Pylospira it is produced by the lateral girdle, or the second lattice-girdle of that group. Therefore Pylospira may be derived phylogenetically from Tetrapyle in the same manner as Larcospira from Amphipyle. Whilst in this latter the first cause of the spiral turning, the unequal growth of both girdle-wings, proceeds from the transverse girdle, in Pylospira it proceeds from the lateral girdle. One of its wings overgrows the other, turning around the sagittal axis. If the second wing do not become developed, the spiral remains simple and represents the subgenus Pylospirema; but if afterwards the second wing follow the example of the first and overgrow it from the other side, we reach the typical form of the second subgenus, Pylospironium, with a double spiral.

Subgenus 1. Pylospirema, Haeckel.

Definition.--Spiral convolutions or turns of the cortical shell simple, only one single wing of the lateral girdle turning around the sagittal axis.

{698}1. Pylospira tetrapyle, n. sp.

Cortical shell with thorny surface, five times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a half times as long as broad. Four internal gates (as in Tetrapyle, between the complete lateral wings of the transverse girdle) kidney-shaped. One principal wing of the lateral girdle turns around the other in one and a half to two simple spiral turns.

Dimensions.--Length of the cortical shell 0.21, breadth 0.15; length of the medullary shell 0.04, breadth 0.03.

Habitat.--Pacific, central area, Station 268, depth 2900 fathoms.

2. Pylospira octopyle, n. sp. (Pl. 49, fig. 4).

Cortical shell with thorny surface, three times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical or nearly hexagonal, with four rounded corners (on the poles of two crossed diagonal axes), one and a third times as long as broad. Eight internal egg-shaped gates (as in Octopyle), between the complete lateral wings of the transverse girdle, and two axial beams in the principal axis. One single wing of the lateral girdle turns around the other in two to three simple spiral turns.

Dimensions.--Length of the cortical shell 0.18, breadth 0.14; length of the medullary shell 0.06, breadth 0.035.

Habitat.--North Pacific, Station 253, depth 3125 fathoms.

Subgenus 2. Pylospironium, Haeckel.

Definition.--Spiral convolutions or turns of the cortical shell double; both wings of the lateral girdle turning around the sagittal axis.

3. Pylospira cymbium, n. sp.

Cortical shell with smooth surface, seven times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a third times as long as broad. Four internal kidney-shaped gates between the complete lateral wings of the transverse girdle (as in Tetrapyle). Both principal wings of the lateral girdle turn round one another in two to two and a half double spiral turns.

Dimensions.--Length of the cortical shell 0.22, breadth 0.17; length of the medullary shell 0.03, breadth 0.025.

Habitat.--Indian Ocean, Madagascar, Rabbe, surface.

{699}Genus 308. Tholospira,[348] n. gen.

Definition.--#Lithelida# with double, trizonal or Larnacilla-shaped medullary shell; cortical shell subspherical or lentelliptical constructed of a simple or double spiral of the sagittal girdle (or third cortical girdle); the spiral lamella revolving around the transverse axis.

The genus Tholospira represents the third genus of Larcospirida. Whilst the spiral growth of the cortical shell is produced in Larcospira by the first (transverse) girdle of the Diplozonaria, in Pylospira by the second (lateral) girdle, in Tholospira it is effected by the third or sagittal girdle, which we found complete in Pylonium. If in this genus one wing of the sagittal girdle overgrow the other remaining one and turn around the transverse axis, we get Tholospirema, the first subgenus of our genus, with simple spiral; but if afterwards the second wing follow the example of the first, and overgrow it from the other side, we get Tholospironium, with double spiral.

Subgenus 1. Tholospirema, Haeckel.

Definition.--Spiral convolutions or turns of the cortical shell simple, only one single wing of the sagittal girdle turning around the transverse axis.

1. Tholospira nautiloides, n. sp.

Cortical shell with smooth surface, five times as long as the lentelliptical medullary shell. Perimeter of the lateral plane elliptical, one and a half times as long as broad. Four internal kidney-shaped gates (between the lateral wings of the transverse girdle, as in Tetrapyle). One wing of the sagittal girdle turns around the other in two to two and a half simple spiral turns.

Dimensions.--Length of the cortical shell 0.24, breadth 0.18; length of the medullary shell 0.05, breadth 0.04.

Habitat.--Indian Ocean, between Ceylon and Socotra, Haeckel, surface.

2. Tholospira spinosa, n. sp.

Cortical shell covered with numerous (sixty to eighty or more) simple, bristle-like radial spines, about the length of the shell. Perimeter of the lateral plane nearly quadrangular, with four rounded corners (on the poles of two crossed diagonal axes), one and a half times as long as broad. Eight internal egg-shaped gates (between the lateral wings of the transverse girdle and two axial {700}beams in the principal axes, as in Octopyle). One wing of the sagittal girdle turns around the other in two to three simple spiral turns.

Dimensions.--Length of the cortical shell 0.27, breadth 0.18; length of the medullary shell 0.04, breadth 0.03.

Habitat.--South Pacific, Station 288, surface.

3. Tholospira dendrophora, n. sp. (Pl. 49, fig. 6).

Cortical shell covered with numerous (forty to fifty or more) branched radial spines, about half as long as the shell; each spine with two to six dichotomous branches. Perimeter of the lateral plane elliptical, one and a third times as long as broad. Eight internal egg-shaped gates, as in the foregoing species. One single wing of the sagittal girdle turns around the other in three to four spiral turns.

Dimensions.--Length of the cortical shell 0.22, breadth 0.17; length of the medullary shell 0.05, breadth 0.04.

Habitat.--Pacific, central area, Station 272, depth 2600 fathoms.

Subgenus 2. Tholospironium, Haeckel.

Definition.--Spiral convolutions of the cortical shell double; both wings of the sagittal girdle turning around the transverse axis.

4. Tholospira hystrix, n. sp.

Cortical shell covered with numerous (sixty to eighty or more) simple conical spines, about half as long as the shell. Perimeter of the lateral plane hexagonal, one and a half times as long as broad. Four internal kidney-shaped gates, as in Tetrapyle. Both wings of the sagittal girdle turn round one another in two to two and a half double spiral turns.

Dimensions.--Length of the cortical shell 0.21, breadth 0.14; length of the medullary shell 0.04, breadth 0.03.

Habitat.--North Atlantic, Station 354, surface.

5. Tholospira cervicornis, n. sp. (Pl. 49, fig. 5).

Cortical shell covered with numerous (forty to fifty or more) branched radial spines; each spine antler-shaped, about as long as the medullary Larnacilla-shell, with eight to twelve dichotomous branches (similar to Cromyodrymus abietinus, Pl. 30, fig. 6). Perimeter of the lateral plane elliptical, one and a third times as long as broad. Four internal kidney-shaped gates, as in Tetrapyle. Both wings of the sagittal girdle turn round one another in one and a half to two double spiral turns.

Dimensions.--Length of the cortical shell 0.2, breadth 0.15; length of the medullary shell 0.03, breadth 0.025.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

{701}Genus 309. Spironium,[349] n. gen.

Definition.--#Lithelida# with double, trizonal or Larnacilla-shaped medullary shell; cortical shell subspherical or lentelliptical, constructed of two crossed spirals, which arise from both lateral wings of one girdle (commonly the lateral girdle) and revolve in an opposite diagonal direction around the principal axis.

The genus Spironium differs in a very remarkable manner from all foregoing Lithelida, and is distinguished by a quite peculiar mode of growth. It is most nearly allied to Larcopyle, and may, like this, be derived from Amphipyle (or rather from Larnacilla, beginning to transform into Amphipyle). But whilst in Larcopyle one of the two wings of the lateral girdle overgrows the other in the direction of the transverse axis (turning around the principal axis), here in Spironium both lateral wings begin at the same time to grow out from the lateral sides of the Larnacilla-shaped medullary shell; the most remarkable thing is, however, that the direction of growth in the wings is diverse from the beginning: the left wing grows downwards and turns around the lower (aboral) pole of the principal axis, the right wing grows upwards and turns around the upper (oral) pole of the same axis. Thus both wings of the lateral girdle are crossed in diagonal axes, and with increasing growth one overgrows the other in the direction of these diagonals, so as to resemble the figure 8 in shape. The open gates remaining between the turnings of the girdle become afterwards closed on the surface by irregular lattice-work, and so the whole cortical shell assumes finally a spherical, ellipsoidal, or lentelliptical form. Its surface sometimes becomes covered with simple or branched radial spines. In the interior the eight characteristic egg-shaped gates of Octopyle are commonly (or constantly?) visible, two strong radial beams in the principal axis arising from the poles of the lentelliptical medullary shell.

Subgenus 1. Spironetta, Haeckel.

Definition.--Surface of the shell smooth or rough, but not with radial spines.

1. Spironium octonium, n. sp. (Pl. 49, fig. 7).

Cortical shell lentelliptical, its breadth (or transverse axis) surpassing considerably the length (or the principal axis). Surface thorny and somewhat hump-backed. The spiral wings of the transverse girdle have about the same breadth as the eight internal gates between them and the axial beams.

Dimensions.--Length of the cortical shell (or principal axis) 0.15, breadth (or transverse axis) 0.2; length of the medullary shell 0.05, breadth 0.04.

Habitat.--South Atlantic, west of Tristan da Cunha, Station 332, depth 2200 fathoms.

{702}2. Spironium diagonale, n. sp.

Cortical shell nearly spherical, four times as great as the subspherical medullary shell. Surface rough. The spiral wings of the transverse girdle about half as broad as the eight internal gates between them and the axial beams.

Dimensions.--Diameter of the cortical shell 0.16, of the medullary shell 0.04.

Habitat.--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

Subgenus 2. Spironilla, Haeckel.

Definition.--Surface of the shell covered with simple or branched radial spines.

3. Spironium spinosum, n. sp.

Cortical shell subspherical, five times as great as the subspherical medullary shell. Surface covered with numerous (sixty to eighty or more) simple, bristle-like radial spines, longer than the shell. The spiral wings of the transverse girdle of about the same breadth as the eight internal gates between them and the axial beams.

Dimensions.--Diameter of the cortical shell 0.2, of the medullary shell 0.04.

Habitat.--Pacific, central area, Station 274, surface.

4. Spironium arbustum, n. sp.

Cortical shell lentelliptical, its breadth surpassing its length considerably. Surface covered with numerous (forty to sixty or more) thin radial spines, about as long as the greatest diameter of the shell; each spine with two to six lateral branches, which are either simple or again branched (similar to Cromyodrymus abietinus, Pl. 30, fig. 6). The spiral wings of the transverse girdle only half as broad as the eight internal gates between them and the strong beams of the principal axis.

Dimensions.--Length of the cortical shell 0.12, breadth 0.15; length of the hexagonal medullary shell 0.05, breadth 0.04.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

Family XXX. #STREBLONIDA#, n. fam. (Pl. 49, figs. 8, 9).

Definition.--#Larcoidea# with asymmetrical, spiral, polythalamous shell, composed of a variable number of roundish chambers, which form together an ascending spiral; both halves of the shell unequal. Primordial chamber either simple or Larnacilla-shaped.

The family #Streblonida# comprises those #Larcoidea# in which a number of chambers is arranged in an ascending spiral, round a simple or trizonal primordial chamber, like winding stairs. They show the same spiral structure as in the foregoing {703}family, but whilst in the Lithelida the spiral line lies in one plane (as in Nautilus), in the Streblonida it ascends like a screw (as in Helix). Therefore the former have the same relation, regarding the spiral structure, to the nautiloid Polythalamia as the latter to the turbinoid Foraminifera. Indeed the single forms of Streblemida repeat in their special structure the characteristic genera of Turbinoida, such as Globigerina, Rosalina, Pulvinulina, Hastigerina, &c. As in these calcareous turbinoid Foraminifera, so also in the analogous siliceous Streblonida the distinction of species is very difficult and open to many objections.

The number of species in this family is very small; all are rare and for the most part very opaque and difficult to understand, so that the following distinction of a dozen species can have only a provisional value. To get a complete idea of their peculiar structure, the shell must be turned and observed from different sides, and thus their full study requires yet much time and work. There are to be found evident transitional forms between them and the Lithelida on the one hand and the Soreumida on the other. Besides this, most species of Streblonida seem to have more inclination to individual varieties and abnormalities than the majority of the other Radiolaria.

The general form of the whole shell is in the Streblonida sometimes more egg-shaped or even subspherical, at other times more top-like or conical, sometimes nearly discoidal. The height of the shell (or the vertical axis of the ascending spiral) is occasionally larger, at other times smaller than the breadth (or the greatest horizontal diameter, perpendicular to the height). Some very flat forms seem to approach the Lithelida. With regard to the internal screw-formation, the shell of all Streblonida is asymmetrical.

The number of the aggregated incomplete chambers is commonly between ten and twenty, but ascends sometimes to thirty, forty, or more. Sometimes the size of all the chambers is nearly the same, sometimes they increase gradually, occasionally also very rapidly. The primordial chamber (or the first and oldest) seems to be commonly the smallest, and inversely, the last and youngest chamber, the largest. But sometimes (in Streblopyle) also the contrary may be the case. The form of the single chambers is very variable, from the spherical or hemispherical through all transitions leading to irregular roundish or longish forms. The network is commonly irregular, with small roundish pores of different sizes, but sometimes also regular, circular. The surface of the shell is commonly smooth or rough, rarely covered with radial spines. In most species the reticulation and particularly the separation of the chambers is more or less incomplete.

As in the Lithelida, so also in the Streblonida we can distinguish two subfamilies. In the Streblacanthida (Streblonia, Streblacantha) the primordial chamber is a simple, spherical, subspherical, or lentelliptical latticed shell. In the Streblopylida (Streblopyle) the primordial chamber is trizonal or Larnacilla-shaped, as in the greater number of #Larcoidea#, composed of three elliptical latticed girdles of unequal size, perpendicular one to another, and surrounding a simple central chamber. As in the Lithelida, so also {704}here we cannot certainly say whether the former have originated from the latter by reduction of the Larnacilla-shell, or whether both groups be of different origin. The latter is perhaps more probable. This family as well as the foregoing requires a much more careful study than I could give to it.

Synopsis of the Genera of Streblonida.

------------------------------------------------------------------------- I. Subfamily Streblacanthida. Primordial chamber simple, spherical or lentelliptical. ------------------------------------------------------------------------- Shell without radial spines, 310. Streblonia.

Shell with radial spines, 311. Streblacantha. ------------------------------------------------------------------------- II. Subfamily Streblopylida. Primordial chamber trizonal or Larnacilla-shaped. ------------------------------------------------------------------------- Shell without radial spines, 312. Streblopyle.

Genus 310. Streblonia,[350] n. gen.

Definition.--#Streblonida# with simple, spherical, subspherical, or lentelliptical primordial chamber, beginning the screw-like series of spirally ascending chambers. Surface smooth or thorny, without radial spines.

The genus Streblonia contains those Streblonida in which a variable number of roundish, subspherical, or longish chambers form a screw-like aggregate, beginning with a quite simple primordial chamber. The special order of the complex spiral offers interesting resemblances to different genera of the calcareous Foraminifera, from which I have taken the corresponding name of the species. The whole form of the shell is sometimes more egg-shaped or subspherical, at other times more top-like or conical, occasionally very flat. Its surface is smooth or rough, but not covered with radial spines.

1. Streblonia globigerina, n. sp.

Shell subspherical, thick walled, clustered, with eight to ten nearly spherical chambers, of rapidly increasing size, the tenth chamber about twelve times as broad as the first. Breadth of the shell nearly equal to the height. Pores subregular, circular, hexagonally formed, of about the same breadth as the bars; about sixteen on the breadth of the tenth chamber. (Resembles very much the common Globigerina.)

Dimensions.--Breadth of the shell 0.18, height 0.16.

Habitat.--North Pacific, Station 253, depth 3125 fathoms.

2. Streblonia uvigerina, n. sp.

Shell nearly egg-shaped, clustered, with eight to eleven subspherical chambers of gradually increasing size, the tenth chamber about six times as broad as the first. Breadth of the shell about {705}half its height. Pores of the shell subregular, circular, about twice as broad as the bars; about twenty on the breadth of the tenth chamber. (Resembles some species of Uvigerina.)

Dimensions.--Breadth of the shell 0.11, height 0.23.

Habitat.--South Atlantic, Station 332, depth 2200 fathoms.

3. Streblonia polymorphina, n. sp.

Shell egg-shaped, thin walled, with twelve to fourteen roundish chambers of rapidly increasing size, the tenth chamber about seven times as broad as the first. Breadth of the shell about two-thirds of the height. Pores irregular roundish, twice as broad as the bars; about twenty on the tenth chamber. (Resembles certain forms of Polymorphina.)

Dimensions.--Breadth of shell 0.22, height 0.14.

Habitat.--Pacific, central area, Station 266, depth 2750 fathoms.

4. Streblonia bulimina, n. sp.

Shell nearly egg-shaped, thick walled, clustered, with fourteen to eighteen egg-shaped chambers of rapidly increasing size, the tenth chamber about eight times as broad as the first. Breadth of the shell about two-thirds of the height. Pores irregular, roundish, half as broad as the bars; about twelve on the breadth of the tenth chamber. (Resembles closely Bulimina.)

Dimensions.--Breadth of the shell 0.17, height 0.24.

Habitat.--Pacific, central area, Station 268, depth 2900 fathoms.

5. Streblonia rosalina, n. sp.

Shell top-shaped or flatly conical, with twelve to sixteen chambers of gradually increasing size, the tenth chamber about four times as broad as the first. Breadth of the shell twice as large as the height. Pores subregular, circular, very small, of the same breadth as the bars; about twelve on the breadth of the tenth chamber. (Resembles some forms of Rosalina.)

Dimensions.--Breadth of the shell 0.27, height 0.13.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

6. Streblonia planorbulina, n. sp.

Shell very flatly conical, nearly lenticular or discoidal, with twenty to twenty-five chambers of nearly equal size, the tenth chamber a little broader than the first. Breadth of the shell exceeds five to six times the height. Pores subregular, circular, very small, half as broad as the bars; about eight on the breadth of the tenth chamber. (Resembles closely Planorbulina.)

Dimensions.--Breadth of the shell 0.3 to 0.4, height 0.06 to 0.07.

Habitat.--Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

{706}7. Streblonia pulvinulina, n. sp.

Shell top-shaped or flatly conical, with thirty to forty chambers of slowly increasing size, the tenth chamber about three times as broad as the first. Breadth of the shell exceeds three times the height. Pores circular, subregular, very small, about one-third as broad as the bars; about thirty in the breadth of the tenth chamber. (Resembles closely Pulvinulina.)

Dimensions.--Breadth of the shell 0.25, height 0.08.

Habitat.--Pacific, central area, Station 263, depth 2650 fathoms.

Genus 311. Streblacantha,[351] n. gen.

Definition.--#Streblonida# with simple, spherical, subspherical, or lentelliptical primordial chamber, beginning the screw-like series of spirally ascending chambers. Surface covered with radial spines.

The genus Streblacantha differs from the nearly allied Streblonia only in the covering of radial spines, and bears therefore the same relation to it as Hastigerina has to Globigerina amongst the similar calcareous Polythalamia.

1. Streblacantha siderolina, n. sp. (Pl. 49, figs. 8, 8_a_).

Streblonia siderolina, Haeckel, 1883, MS.

Shell flatly conical, with fourteen to sixteen nearly hemispherical chambers of gradually increasing size, the tenth chamber about six times as broad as the first. Breadth of the shell nearly equal to the height. Pores subregular, circular, hexagonally framed, twice as broad as the bars; about nine pores on the breadth of the tenth chamber. Surface covered with numerous short conical radial spines, one-fourth to one-sixth as long as the diameter of the shell.

Dimensions.--Breadth of the shell 0.15, height 0.17.

Habitat.--South Pacific, Station 298, depth 2225 fathoms.

2. Streblacantha calcarina, n. sp.

Shell conical, with sixteen to eighteen roundish chambers of gradually increasing size, the tenth chamber about three times as broad as the first. Breadth of the shell about one and a half times the height. Pores irregular, roundish. Surface covered with numerous strong conical radial spines, about half as long as the diameter of the shell.

Dimensions.--Breadth of the shell 0.24, height 0.17.

Habitat.--South Pacific, Station 285, depth 2375 fathoms.

{707}3. Streblacantha hastigerina, n. sp.

Shell nearly spherical, clustered, with nine to eleven nearly spherical chambers of rapidly increasing size, the tenth chamber about six times as broad as the first. Breadth of the shell nearly equal to the height. Pores subregular, circular, of about the same breadth as the bars. Surface bristly, covered with numerous very thin and long, needle-shaped radial spines, longer than the diameter of the shell. (Resembles closely Hastigerina.)

Dimensions.--Breadth of the shell 0.18, height 0.15.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

Genus 312. Streblopyle,[352] n. gen.

Definition.--#Streblonida# with trizonal lentelliptical medullary shell (composed like Larnacilla of three elliptical dimensive girdles surrounding one simple central primordial chamber). From this begins a screw-like series of spirally ascending chambers. Surface smooth or thorny, without radial spines.

The genus Streblopyle presents externally the same appearance and contour as Streblonia, and is composed like this of a variable number of chambers, ascending screw-like around the axis of the spiral shell. The first or primordial chamber, however, in which the growth begins, is in Streblonia a simple spherical shell, but in Streblopyle a trizonal shell or Larnacilla-shell (compare above, p. 600). The chambers are very incompletely separated, and comparatively much larger, their number much smaller than in Streblonia. The structure in the species of this genus is difficult to understand.

1. Streblopyle helicina, n. sp. (Pl. 49, fig. 9).

Shell helicoid, one and a third times as high as broad, with eight to twelve incomplete semizonal chambers, ascending spirally from the lateral half girdle of the lentelliptical medullary shell, octopyle-shaped, and enveloping it in three to four spiral turnings. The height of the whole cortical shell equals nearly five times the height of the trizonal medullary shell. Pores irregular, roundish. Surface of the shell rough or nearly smooth. (This species seems to be nearly allied to Spironium octonium.)

Dimensions.--Breadth of the spiral cortical shell 0.18, height 0.24; breadth of the medullary shell 0.04, height 0.05.

Habitat.--Pacific, central area, Station 266, depth 2750 fathoms.

2. Streblopyle spirulina, n. sp.

Shell egg-shaped or nearly spherical, about as high as broad, with eight to nine semizonal chambers, ascending spirally from the subspherical trizonal medullary shell, and enveloping it in {708}four to five turnings. The sixth chamber twice as broad as the trizonal medullary shell. Pores irregular, roundish. Surface of the shell thorny.

Dimensions.--Breadth of the spiral cortical shell 0.27, height 0.25; breadth of the medullary shell 0.05, height 0.06.

Habitat.--Pacific, central area, Station 265, depth 2900 fathoms.

Family XXXI. #PHORTICIDA#, Haeckel (Pl. 49, figs. 10, 11).

Phorticida, Haeckel, 1881, Prodromus, p. 464.

Definition.--#Larcoidea# with quite irregular monothalamous shell, representing irregular modifications of an original lentelliptical latticed shell; the irregular cortical shell encloses a regular or subregular, lentelliptical or trizonal medullary shell.

The family Phorticida comprises a small number of #Larcoidea# in which a subregular, trizonal, lentelliptical medullary shell is enclosed by an irregular simple or spongy cortical shell. The lattice-work of the latter is sometimes simple and complete, at other times incomplete, with open gates (as in the Pylonida), sometimes also spongy. Its form is always more or less irregular, roundish, often dimply or tuberous; different from most other #Larcoidea#.

The medullary shell is constantly a regular or subregular Larnacilla-shell, composed of three elliptical latticed girdles of different sizes, perpendicular one to another. This leaves no doubt that the Phorticida are true #Larcoidea#. The connection of it with the cortical shell is rarely effected by radial beams, commonly by two opposite latticed wings, which are identical with the lateral halves of the transverse girdle in the Pylonida diplozonaria (Amphipyle, Tetrapyle). Often also between this transverse and a second (lateral) girdle there remain large open gates, so that the affinity between these Phorticida and the Pylonida cannot be doubted. In other cases these gates become closed, so that they more nearly approach the Larnacida. From both families they differ by the irregularity of the papillate or tuberous cortical shell. The network is more or less irregular, its surface often thorny, but never covered with symmetrically disposed radial spines.

The central capsule is lentelliptical, encloses the medullary shell, and is enveloped by the cortical shell, as in the nearly allied Pylonida and Larnacida, of which the Phorticida may be regarded as irregular aberrant forms.

Synopsis of the Genera of Phorticida.

Cortical shell simply latticed, 313. Phorticium.

Cortical shell spongy, 314. Spongophortis.

{709}Genus 313. Phorticium,[353] Haeckel, 1881, Prodromus, p. 464.

Definition.--#Phorticida# with irregular cortical shell of simple lattice-work, enclosing a lentelliptical Larnacilla-shaped medullary shell.

The genus Phorticium comprises all Phorticida in which the irregular cortical shell is formed by simple lattice-work, not by spongy framework. We can divide this genus into two subgenera: in Phortopyle (as in the Pylonida) the lattice-work of the cortical shell exhibits large openings or gates; in Phortolarcus these gates are perfectly closed by network; the former may be regarded as abnormal or irregular Pylonida, the latter as modifications of Larnacida.

Subgenus 1. Phortopyle, Haeckel.

Definition.--Lattice-work of the irregular cortical shell incomplete, with large openings or gates.

1. Phorticium pylonium, n. sp. (Pl. 49, fig. 10).

Cortical shell irregular, roundish, about three times as large as the enclosed lentelliptical, regular, Larnacilla-shell, connected with it by some radial beams and irregularly latticed girdles; between these remain four to eight large open gates of irregular roundish form and size; and these gates are the same as in Tetrapyle and Octopyle. This very variable species may be regarded as a monstrosity of those genera of Pylonida; it is very common, but all individuals are more or less unequal; some specimens approach to some common species of Tetrapyle. The surface of the shell is more or less spiny.

Dimensions.--Diameter of the irregular cortical shell 0.12 to 0.18; length of the lentelliptical medullary shell 0.05 to 0.06, breadth 0.035 to 0.045.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific, &c., common, surface and in various depths.

2. Phorticium spironium, n. sp.

Cortical shell irregular, roundish, tuberous, about four times as large as the enclosed subregular Larnacilla-shell, connected with it by some irregular radial beams, and by opposite, spirally begining, irregularly latticed girdles, comparable to those of Spironium; between them remain six to twelve large open gates of irregular size and form. Surface rough. The resemblance to some forms of Spironium makes it probable that this species is a deformity or monstrosity of that genus.

Dimensions.--Diameter of the irregular cortical shell 0.12 to 0.2, of the lentelliptical medullary shell 0.03 to 0.06.

Habitat.--Pacific, central area, Stations 270 to 274, surface, and in various depths.

{710}Subgenus 2. Phortolarcus, Haeckel.

Definition.--Lattice-work of the irregular cortical shell complete, without large openings or gates.

3. Phorticium deforme, n. sp.

Cortical shell irregular, roundish or longish, three times as large as the enclosed subregular, lentelliptical Larnacilla-shell, connected with it by two opposite latticed wings (the halves of the transverse girdle of Tetrapyle). Network of the cortical shell irregular, dense, perfectly closed, without larger openings or gates. Surface thorny. (May be regarded as a monstrous form of Larnacalpis.)

Dimensions.--Diameter of the irregular cortical shell 0.15 to 0.18, of the medullary shell 0.04 to 0.06.

Habitat.--Pacific, central area, Station 272, depth 2600 fathoms.

4. Phorticium abnorme, n. sp.

Cortical shell irregular, roundish, tuberous, with five to ten quite irregular or nearly hemispherical protuberances, which resemble the cupolas of Zonarida. The regular lentelliptical Larnacilla-shell is one-third to one-fourth as large as the enclosing cortical shell, and is connected with it by some irregular radial beams. Lattice-work completely closed, without gates. Surface spiny. (May be regarded as an anomalous form of Zonidium; as in the other species of this variable genus, the individuals are very unequal.)

Dimensions.--Diameter of the irregular cortical shell 0.12 to 0.2, of the medullary shell 0.03 to 0.05.

Habitat.--Atlantic and Pacific, tropical zone, surface, and at various depths.

Genus 314. Spongophortis,[354] Haeckel, 1881, Prodromus, p. 464.

Definition.--#Phorticida# with irregular cortical shell of spongy framework, enclosing a lentelliptical Larnacilla-shaped medullary shell.

The genus Spongophortis differs from Phorticium in the spongy framework of the cortical shell. This encloses the inner Larnacilla-shaped medullary shell either directly, or both shells are separated by a hollow interval, and connected either by radial beams or by latticed lamellæ. Perhaps both these subgenera might be better separated as genera.

{711}Subgenus 1. Stypophorticium, Haeckel.

Definition.--Spongy cortical shell immediately enclosing the lentelliptical medullary shell, without hollow interval.

1. Spongophortis spongiosa, n. sp.

Cortical shell irregular, roundish, rough or tuberous, composed of loose spongy framework, which immediately envelops the lentelliptical central Larnacilla-shell; the diameter of the former becomes about five to six times as large as that of the latter.

Dimensions.--Diameter of the spongy cortical shell 0.15 to 0.25, of the trizonal medullary shell 0.03 to 0.04.

Habitat.--Pacific, central area, Station 274, surface.

Subgenus 2. Spongophorticium, Haeckel.

Definition.--Spongy cortical shell separated by a hollow interval from the lentelliptical medullary shell.

2. Spongophortis radiosa, n. sp.

Cortical shell irregular, roundish, four to five times as large as the enclosed lentelliptical Larnacilla-shell, with which it is connected by ten to twenty irregularly disposed radial beams. Spongy framework compact, about as thick as the medullary shell. Surface covered with numerous short, bristle-shaped, radial spines.

Dimensions.--Diameter of the spongy cortical shell 0.15 to 0.2, of the trizonal medullary shell 0.035 to 0.045.

Habitat.--South Atlantic, Station 332, depth 2200 fathoms.

3. Spongophortis larnacilla, n. sp. (Pl. 49, figs. 11_a_-11_d_).

Cortical shell irregular, roundish, tuberous, three to four times as large as the enclosed lentelliptical Larnacilla-shell, connected with it by two opposite latticed wings (the halves of the transverse girdle of Tetrapyle). Spongy framework compact, about half as thick as the medullary shell. Surface rough. (May be regarded as an abnormal Tetrapyle or Larnacalpis, with an irregular spongy cortical shell.)

Dimensions.--Diameter of the spongy cortical shell 0.16 to 0.2, of the trizonal medullary shell 0.04 to 0.06.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

{712}Family XXXII. #SOREUMIDA#, Haeckel (Pl. 49, figs. 12, 13).

Soreumida, Haeckel, 1881, Prodromus, p. 464.

Definition.--#Larcoidea# with quite irregular polythalamous shell, composed of a variable number of chambers, aggregated without any definite order. Primordial chamber either simple or Larnacilla-shaped.

The family #Soreumida# contains a small number of #Larcoidea#, different from most other #Sphærellaria# in the complete irregularity of the polythalamous shell, which is composed of a variable number of roundish chambers or subspherical latticed shells, aggregated in the form of an irregular heap. We can distinguish in this family only two genera, with very different structure of the central medullary shell or the first chamber beginning the growth; and these correspond to the two subfamilies of the nearly allied Streblonida (p. 704). In Soreuma (as in Streblonia) the first or primordial chamber, from which the growth begins, is like the others, a simple spherical or irregular roundish lattice-shell. In Sorolarcus, however (as in Streblopyle), the first or primordial chamber is a trizonal or Larnacilla-shell. It is not improbable that the former originated phylogenetically from Streblonia, the latter from Streblopyle, by loss of the original spiral order of growth. But it is also possible that these groups have no nearer relation. Among the calcareous Foraminifera a very similar form is represented by Acervulina and its allies.

The general form of the whole shell in the Soreumida is sometimes more egg-shaped or lentelliptical, at other times even subspherical, occasionally quite irregular, tuberous, or clustered. The number of the aggregated chambers is very variable, in Sorolarcus between ten and thirty, in Soreuma ascending to fifty to eighty, sometimes from one hundred to one hundred and fifty and more. Their size is sometimes nearly equal, at other times very different, their form commonly very irregular, roundish, but sometimes also subspherical or egg-shaped. The network of the shell is also commonly irregular, with roundish pores of different sizes. The surface is usually smooth or rough, rarely covered with radial spines.

The central capsule is not known, as I observed only a few skeletons of this family.

Synopsis of the Genera of Soreumida.

Primordial chamber of the shell simple, subspherical or roundish, 315. Soreuma.

Primordial chamber of the shell trizonal or Larnacilla-shaped, 316. Sorolarcus.

Genus 315. Soreuma,[355] Haeckel, 1881, Prodromus, p. 464.

Definition.--#Soreumida# with numerous chambers, aggregated without any regularity around one simple, spherical or subspherical, central chamber.

{713}The genus Soreuma contains those Soreumida in which no trace of any regular structure is found, but all the chambers of the irregular shell are without any order, aggregated around a simple spherical or subspherical central chamber or medullary shell. Soreuma may have originated either from Sorolarcus by loss of the central Larnacilla-shell or from Cenolarcus by irregular apposition of new chambers around the lentelliptical central chamber or simple Larcoid-shell. Some species seem to exhibit a transition to Sorolarcus. Owing to the absolute irregularity of the polythalamous shell Soreuma resembles Acervulina among the Foraminifera.

Subgenus 1. Soreumium, Haeckel.

Definition.--Shell without radial spines.

1. Soreuma irregulare, n. sp. (Pl. 49, fig. 12).

Shell irregular, clustered, or tuberous, composed of a large number (one hundred and twenty to one hundred and fifty or more) of irregular, roundish chambers of very different sizes, the largest four to five times as broad as the smallest. Network very delicate, with very small roundish pores, to five times as broad as the bars. Surface thorny.

Dimensions.--Diameter of the shell 0.3, of the single chambers 0.02 to 0.08.

Habitat.--North Pacific, Station 244, depth 2900 fathoms.

2. Soreuma acinosum, n. sp.

Shell irregularly lentelliptical, with different growth in the three dimensions, composed of a large number (forty to sixty or more) of irregular, roundish chambers of very different sizes, the largest six to eight times as broad as the smallest. Pores subregular, circular, twice as broad as the bars. Surface smooth.

Dimensions.--Length of the shell 0.21, breadth 0.17, height 0.13; diameter of the largest chambers 0.03, of the smallest 0.004.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

3. Soreuma subglobosum, n. sp.

Shell nearly spherical, composed of a variable number (twelve to fifteen or more) of irregularly aggregated subspherical chambers of nearly equal size. Pores subregular, circular, twice as broad as the bars. Surface thorny.

Dimensions.--Diameter of the shell 0.25, of the largest chambers 0.04, of the smallest 0.005.

Habitat.--Pacific, central area, Station 266, depth 2750 fathoms.

{714}4. Soreuma acervulina, n. sp.

Shell quite irregular, cloddy, or tuberous, composed of twenty to thirty (or more) roundish chambers of almost uniform size, the largest twice to three times as broad as the smallest. Pores irregular, roundish. Surface smooth.

Dimensions.--Diameter of the shell 0.18 to 0.24, of the largest chambers 0.06, of the smallest 0.02.

Habitat.--South Pacific, Station 295, depth 1500 fathoms.

Subgenus 2. Soreumidium, Haeckel.

Definition.--Shell with radial spines.

5. Soreuma spinosum, n. sp.

Shell quite irregular, cloddy, or tuberous, composed of thirty to forty subspherical chambers of nearly the same size. Pores subregular, circular, twice as broad as the bars; on the equator of each chamber six to eight pores. Surface thorny, covered with irregularly scattered conical radial spines, about as long as the diameter of the chambers.

Dimensions.--Diameter of the shell 0.17 to 0.25, of the chambers 0.04.

Habitat.--North Pacific, Station 241, depth 2300 fathoms.

6. Soreuma setosum, n. sp.

Shell nearly spherical, composed of sixty to seventy (or more) irregular, roundish chambers of very different sizes, the largest five to six times as broad as the smallest. Pores irregular, roundish. Surface bristly, covered with very numerous, long and thin, bristle-shaped radial spines, about as long as the diameter of the shell.

Dimensions.--Diameter of the shell 0.28, of the chambers 0.005 to 0.03.

Habitat.--Pacific, central area, Station 271, depth 2425 fathoms.

Genus 316. Sorolarcus,[356] n. gen.

Definition.--#Soreumida# with numerous chambers, aggregated irregularly around a trizonal medullary shell or Larnacilla-shell.

The genus Sorolarcus comprises those Soreumida in which the heap of irregularly aggregated chambers encloses a central trizonal medullary shell, by which they demonstrate clearly their descent from Larnacida or Pylonida. The lentelliptical medullary {715}shell exhibits quite the same characteristic structure as that of Larnacilla, being composed of three elliptical latticed girdles, perpendicular one to another. In some species also the beginning of a second system of girdles is clearly indicated, so that there can be no doubt as to their derivation from Amphipyle or Tetrapyle.

Subgenus 1. Sorolarcium, Haeckel.

Definition.--Shell without radial spines.

1. Sorolarcus larnacillifer, n. sp. (Pl. 49, fig. 13).

Shell irregular, clustered, or tuberous, composed of twenty to thirty irregular, roundish chambers of very different size, the largest four to eight times as broad as the smallest, aggregated without order around a central, lentelliptical, Larnacilla-shaped medullary shell. Pores irregular, roundish, twice to four times as broad as the bars. Surface smooth or a little spiny.

Dimensions.--Diameter of the whole shell 0.18, of the central Larnacilla-shell 0.05.

Habitat.--Pacific, central area, Station 266, depth 2750 fathoms.

2. Sorolarcus tetrapylifer, n. sp.

Shell irregularly roundish, clustered, composed of ten to twelve irregular rather long chambers of almost uniform size, the largest twice as broad as the smallest, aggregated without order around a central shell of the structure of Tetrapyle, which encloses an inner trizonal Larnacilla-shell of half the size. Pores irregular, roundish, twice to four times as broad as the bars. Surface spiny.

Dimensions.--Diameter of the whole shell 0.25, of the outer (Tetrapyle-like) medullary shell 0.12, of the inner (Larnacilla-like) shell 0.06.

Habitat.--Pacific, central area, Station 272, depth 2600 fathoms.

Subgenus 2. Sorolarcidium, Haeckel.

Definition.--Shell with radial spines.

3. Sorolarcus terminalis, n. sp.

Shell nearly spherical, composed of fifteen to eighteen irregularly aggregated roundish chambers of nearly equal size; in the centre a lentelliptical Larnacilla-shell. Surface covered with numerous thin, bristle-like radial spines, somewhat longer than the shell.

Dimensions.--Diameter of the whole shell 0.21, of the central Larnacilla-shell 0.05.

Habitat.--North Pacific, Station 244, depth 2900 fathoms.

{716}----

LEGION II. #ACANTHARIA#,

VEL ACTIPYLEA, VEL ACANTHOMETREA (PLS. 129-140).

Acantharia, Haeckel, 1881. Actipylea, Haeckel, 1882. Acanthometrea, Hertwig, 1879. Panacantha, Haeckel, 1878.

Definition.--Radiolaria with simple membrane bounding the central capsule, which is everywhere perforated by innumerable fine pores (disposed either equally or symmetrically). Extracapsulum without phæodium. Skeleton centrogenous (its growth proceeding from the centre), acanthinic (organic, not siliceous). Fundamental form originally spherical.

The legion ACANTHARIA vel ACTIPYLEA, to the extent here defined, was constituted by me, 1878, in my Protistenreich (p. 102) under the name "PANACANTHA." A more accurate definition of this group was given in 1879 by Hertwig under the name ACANTHOMETREA. Both names were replaced by me, 1881, in my Prodromus (pp. 421, 465) by the more convenient name ACANTHARIA. This legion comprises all those Radiolaria which were first described by Johannes Müller, 1858, as Acanthometrae, and also an important part of his Haliomma. In my Monograph (1862, pp. 371-424) I disposed them in three families, Acanthometrida, Diploconida, and Dorataspida.

Although the number of genera and species in this legion is much increased by the rich collection of the Challenger, we can divide all ACANTHARIA into two different orders: #Acanthometra# (without complete lattice-shell) and #Acanthophracta# (provided with a complete lattice-shell).

The ACANTHARIA agree with the SPUMELLARIA in the structure of the simple capsule-membrane, which is perforated by numerous small pores (but constantly devoid of the large main opening, which the NASSELLARIA and PHÆODARIA possess, being hence united as "Merotrypasta"). We can therefore unite both former legions as "Holotrypasta" (compare above, pp. 5, 6); but in many ACANTHARIA (if not in all?) the numerous small pores of the capsule-membrane exhibit a certain peculiar arrangement not observed in the SPUMELLARIA; therefore the latter can be regarded as true "Peripylea" in opposition to the former as "Actipylea."

The peculiar main character of all ACTIPYLEA or ACANTHARIA is determined by the chemical constitution of their skeleton, which is not silex, but a peculiar organic substance, called by me in 1862 "acanthin" (Monogr. d. Radiol., pp. 30, 32). In all other Radiolaria the skeleton is composed of silex or of a silicate. But besides this {717}chemical difference, an important morphological character of the skeleton also separates the ACANTHARIA from all other Radiolaria: in the latter the skeleton is never centrogenous or arising from the centre of the capsule; in strict opposition to this general fact the skeleton of all ACANTHARIA is centrogenous, composed of radial spines, which arise from the central point of the capsule and pierce its membrane. These characteristic "radial spines of acanthin," arising from the centre, are never hollow (as formerly was supposed), but constantly solid. Their form is extremely variable, and most important for the distinction of genera and species; but more interesting from a general point of view is their peculiar arrangement or disposition.

The regular disposition of twenty radial spines has general value almost for all ACANTHARIA, with the exception only of the small group of #Actinelida#. In this latter group the number of radial spines is either more or less than twenty, and their disposition is either quite irregular or follows a peculiar rule. The number of individuals of these #Actinelida#, compared with that of the other ACANTHARIA, may be scarcely 1 per cent., whilst the latter have more than 99 per cent.; the number of observed species is in the former about 5 per cent., in the latter about 95 per cent. Nevertheless the small group of #Actinelida# is very important, being probably the ancestral group from which all other ACANTHARIA have been phylogenetically derived. These other ACANTHARIA, with twenty regularly disposed radial spines, represent the two large groups of #Acanthonida# and #Acanthophracta#. For short and clear distinction of these two groups of ACANTHARIA, we will call the #Actinelida# (with irregular number and disposition of radial spines) Adelacantha, in opposition to the Icosacantha (#Acanthonida# and #Acanthophracta#), which all possess twenty regularly disposed radial spines.

Johannes Müller, the great zoologist, to whom we are indebted for the first detection and accurate knowledge of the #Acanthometra#, already recognised the regularity in the peculiar disposition of their twenty radial spines (Abhandl. d. k. Akad. d. Wiss. Berlin, 1858, pp. 12, 37). In honour of my great master I have called this regular disposition the "Müllerian law of spine disposition," and have given a full explanation of it in my Monograph (1862, pp. 40-45, 371, 372). With regard to its general value for all Icosacantha (#Acanthonida# and #Acanthophracta#), we might also call this promorphological Müllerian law "the Icosacanthan law."

In 1862 I had already given the following precise definition of this "Icosacanthan law" (loc. cit., p. 40):--"Between two poles of a spineless axis are regularly disposed five parallel zones, each with four radial spines; the four spines of each zone are equidistant one from another, and also equidistant from each pole; and the four spines of each zone are so alternating with those of each neighbouring zone, that all twenty spines together lie in four meridian planes, which intersect one another at an angle of 45°." For the clear conception of this remarkable Müllerian law, and for the complete understanding of its high value for the complicated {718}morphology of all Icosacantha, it is the most profitable way to retain constantly in mind for comparison the figure of a terrestrial globe with its axis and zones. The axis of the globe is the spineless axis of all Icosacantha, around which all twenty spines are symmetrically disposed; it is perpendicular to the bisecting equatorial plane, in which lies the middle of the five parallel zones; therefore the four spines, crossed perpendicularly in this equatorial plane, are called the equatorial spines (_c_1 to _c_4 in the figures of Pls. 131-140); often, and mainly in the family Quadrilonchida (Pl. 131), these four equatorial spines are much larger or of a peculiar form, different from that of the sixteen other spines. Each pair of the four equatorial spines lies in one equatorial axis, and this latter is perpendicular to the crossing axis, in which lies the other pair of opposite spines. We may regard these two equatorial diameters, perpendicular one to another and to the spineless axis, as the two perradial axes or primary axes. Correspondingly the two meridian planes, which are determined by one perradial axis and the spineless axis, may be called the two primary or perradial meridian planes.

The globe is divided by the equatorial plane into two equal halves, the northern and the southern hemisphere. In each hemisphere there are disposed quite symmetrically eight radial spines, the distal ends of which fall in two parallel circles, a larger tropical circle (nearer to the equator) and a smaller polar circle (nearer to the pole of the spineless axis). Therefore we call the four spines of the former the "tropical spines" and the four spines of the latter the "polar spines." The angle between the former and the equatorial plane is about 30°, the angle between the latter and that plane about 60°.

The eight polar spines (four northern and four southern) lie in the same two meridian planes as the four equatorial spines. Therefore in each of these two perradial planes lie six radial spines, opposite in pairs; two equatorial and four polar spines. Commonly all eight polar spines are of the same size and form; and often they are also equal to the eight tropical spines; but in some cases (e.g., in some species of Quadrilonchida) they are much smaller than the twelve other spines, and sometimes even rudimentary. In all figures of the Pls. 131-140 (and also in my Monograph, 1862, Taf. xv.-xxii.) the polar spines of the northern circle are marked by the characters _a_1 to _a_4, the polar spines of the southern circle by the characters _e_1 to _e_4. In the first perradial meridian plane lie _a_1 and _a_3, _e_1 and _e_3, in the second _a_2 and _a_4, _e_2 and _e_4.

The eight tropical spines lie between the eight polar and the four equatorial spines, four in each hemisphere; their distal points fall in two parallel circles, which correspond exactly to the two tropics of the globe. Therefore the four northern tropical spines may be called "canceral spines" (as their ends fall in the Tropic of Cancer) and the four southern correspondingly "capricornal spines" (as their points lie {719}in the Tropic of the Capricorn). In the figures of the Pls. 131-140 (as well as in my Monograph, 1862, Taf. xv.-xxii.) the four northern or canceral spines are marked by the characters _b_1 to _b_4, and the four southern or capricornal spines by the characters _d_1 to _d_4. Also the eight tropical spines lie (crossed in pairs) in two meridian planes; they do not lie, however, in those perradial planes, in which are placed the twelve other spines; but in two different meridian planes, crossing the former at angles of 45°; we call these the "secondary" or "interradial" meridian planes. Each of these planes is determined by the spineless axis and by two crossed interradial or secondary axes; in each of the latter lie two opposite tropical spines. In the first interradial meridian plane lie _b_1 and _b_3, _d_1 and _d_3, in the second _b_2 and _b_4, _d_2 and _d_4.

It is a most interesting and important fact, that in all Icosacantha (#Acanthonida# and #Acanthophracta#) this regular disposition of the twenty spines (in five parallel zones and four meridian planes) becomes constantly preserved by heredity, whilst the form and size of the different spines are extremely varied by adaptation.

Only in a minority of the Icosacantha are all twenty spines perfectly equal or nearly equal in size and form; and then it is often very difficult to distinguish the different zones in their disposition. But in far the greater part the size or the form of the twenty spines becomes different in different zones; and then we can commonly distinguish easily the five different zones. Firstly, in all Quadrilonchida and Dorataspida, the four equatorial are distinguished from the sixteen other spines either by form or by size, and often in a very remarkable degree. As soon as these four principal spines are recognised, it is easy to determine also the sixteen others; for the eight polar spines lie in the same two (perradial) meridian planes as the former, whilst the eight tropical spines lie in two different (interradial) meridian planes, intersecting the two former at angles of 45°. Commonly, therefore, this distinction is rather easy.

In the majority of the Icosacantha all four equatorial spines are exactly of the same form and size. But in four families the two opposite spines of one equatorial axis are much larger, or of another form, than those of the crossing axis. This is the case in the Amphilonchida, Belonaspida, Hexalaspida, and Diploconida. Therefore we here call the major equatorial axis (with larger spines) the "hydrotomical axis," and the minor axis (with smaller spines) the "geotomical axis." Correspondingly, the meridian plane, in which the two larger equatorial spines are placed (_c_1, _c_3) and the appertaining four polar spines (_a_1, _a_3, _e_1, _e_3) may be called the "hydrotomical plane"; in the remarkable family of Hexalaspida (Pl. 139) all six spines of this hydrotomical plane are much larger than the other fourteen. Perpendicular to this plane is the second perradial meridian plane, which we call the "geotomical plane"; in it lie the two smaller equatorial spines (c2, c4) and the corresponding four polar spines (_a_2, _a_4, _e_2, _e_4). In some Hexalaspida (Hexonaspis and Hexacolpus) the six spines of the hydrotomical plane become so preponderant that {720}the other fourteen spines appear rudimentary; and in some of them the two equatorial spines of the hydrotomical plane are much larger than the four polar spines of the same plane. This curious relation reaches its maximum in the Diploconida (Pl. 140).

The different development of the two equatorial axes (of the larger hydrotomical and the smaller geotomical axis) is the first and most important cause of the peculiar forms, which are produced in the four cited families. We derive these terms also from the metaphor of the terrestrial globe. The hydrotomical plane is that meridian plane of the globe which intersects almost only the water-hemisphere (the island of Ferro in the Atlantic, the island of Pandora in the Pacific). Perpendicular to this is the geotomical plane, the meridian of which intersects great land-masses in both hemispheres (Bombay in India, Athabasca in Canada). Both poles of the smaller geotomical axis are everywhere equal (the East Indian and the Western American). However, both poles of the larger hydrotomical axis (the eastern Atlantic and the western Pacific) are in some genera very different, e.g., in Amphibelone among the Amphilonchida, and in Zygostaurus among the Quadrilonchida. In this case we call the anterior (commonly more developed) pole of the hydrotomical axis the frontal pole, the opposite posterior (commonly smaller) the caudal pole (Pl. 131, figs. 7, 8; Pl. 132, figs. 9, 10). On both sides of these (right and left) lie symmetrically the two equal poles of the geotomical lateral axis.

The promorphology of the ACANTHARIA demonstrates that the geometrical fundamental form in those groups is different. In the majority of the ACANTHARIA, where the two equatorial axes are equal, that form is a double square-pyramid or a "quadrate octahedron"; the four equal equatorial spines indicate the two diagonals of the square, which is the common base of the united regular four-sided pyramids; their common axis is the spineless axis of the body; the ends of the polar spines fall on the edges of the pyramids, while the ends of the tropical spines fall on the halving lines of their faces. However, in those ACANTHARIA in which the two equatorial axes become different, the square double pyramid becomes changed into a rhombic double pyramid; the common base of the united pyramids is thus a rhombus; the hydrotomical axis is the larger, the geotomical axis the smaller diagonal of the rhombus.

Opposed to the Icosacantha, under the name "Adelacantha," is the small group of Actinelida, in which the number and disposition of the radial spines is variable, not determined by the Müllerian law. Probably this group is the common ancestral stock, from which the Icosacantha have been derived by gradual development of their peculiar disposition. Probably the oldest and most primitive form of all ACANTHARIA is Actinelius, in which a variable and undetermined (often very large) number of radial spines is united in one common central point, and therefore forms a needle-sphere. Whilst here all spines (often more than a hundred) are of equal size and form, in the nearly allied Astrolophus large and small spines are intermingled. Both genera together form the small ancestral family of Astrolophida. In the strange family of Litholophida the radial spines do not {721}radiate within a spherical space (equally disposed in all directions), but within a quadrant or even an octant, forming a conical brush or pencil.

One very remarkable form of #Actinelida# is Actinastrum, forming the transition from these Adelacantha to the common regular Icosacantha. In the two observed species of Actinastrum we find thirty-two radial spines, twenty of which are disposed after the Müllerian law, as in the Icosacantha. The other twelve are four interradial equatorial spines (lying in the two secondary meridian planes) and eight perradial tropical spines (lying in the two primary meridian planes). Therefore here in each primary meridian plane are placed ten spines (two equatorial, four tropical, and four polar spines), whereas in each secondary meridian plane are placed six spines (two equatorial and four tropical). But here also all thirty-two spines are so regularly placed that their free distal ends fall into five parallel zones, four in each polar zone, eight in each tropical zone, and eight in the equatorial zone.

The Central Junction of the radial spines in the ACANTHARIA becomes effected in four different ways:--(1) by simple apposition of the pyramidal central ends or bases; (2) by a basal leaf-cross, or by broad wings, four on each spine, supported one upon the other; (3) by a central concrescence of the meeting bases of all the twenty spines, growing perfectly together; and (4) by a concrescence in pairs of every two opposite spines. The most common and probably the original mode of junction is the first--by pyramidal apposition; the spines at the central base are pointed in the form of a pyramid, and the triangular faces of the neighbouring pyramids are simply placed upon one another. Often the small basal pyramids are imperfectly separated from the spines by an annular constriction. Commonly the basal pyramids of the four equatorial spines are six-sided, those of the sixteen other spines five-sided.

The second mode of junction, by a basal leaf-cross, is developed from the first and appears as a strengthening or a mechanical elaboration of it. Immediately above the basal pyramid arise from its radial edges four thin and broad triangular leaves or wings, and the meeting edges of the neighbouring wings are in apposition one with the other, so that between the bases of every three or four neighbouring spines a hollow pyramidal space remains open. The apex of such a pyramidal space is directed towards the centre of the body, but separated from it by the small basal pyramid; its open base is directed outwards. The twenty-two hollow pyramidal spaces are disposed regularly in four different groups:--(A) Four equatorial spaces, four-sided, each limited by two equatorial and two tropical spines (one canceral and one capricornal); (B) eight perizonal spaces (four northern and four southern), four-sided, each limited by one equatorial, two tropical, and one polar spine; (C) eight peripolar spaces (four northern and four southern), three-sided, each limited by one tropical and two polar spines; (D) two polar spaces (one northern and one southern), four-sided, each limited by four neighbouring polar spines.

{722}The third mode of junction, by central concrescence of all twenty spines, was formerly regarded by me as an important peculiarity, sufficient for the separation of subfamilies and genera (Monogr. d. Radiol., 1862, pp. 399, 401; Prodromus, 1881, p. 466). But I found afterwards that in many species where the twenty spines commonly remain separated, accidentally they grow perfectly together and form one single piece of acanthin--a starrulet with twenty rays. Therefore I now think it is more natural to divide those species only into different subgenera.

A fourth and a very different mode of junction, quite sufficient for the distinction of different families, is the concrescence in pairs of every two opposite spines, lying in one diameter (in Acanthochiasma and Chiastolus). Here we obtain a number of "diametral spines" (each composed of two originally opposed radial spines) and all these diametral spines are crossed loosely near the central point of the body without any solid and permanent apposition (Chiastolida). However, in some species of this peculiar family the central part of the diametral spines is twisted like a screw or spirally convoluted (Pl. 129, figs. 2, 3).

The Form of the Radial Spines in the ACANTHARIA is extremely varied, and constitutes the main characters for the distinction of nearly four hundred species. But all these different forms may be reduced phylogenetically to three different fundamental forms:--(a) the cylindrical (with circular transverse section), (b) the two-edged (with elliptical or lanceolate transverse section), and (c) the four-edged (with square transverse section). No doubt the first (a) is the original primitive form, from which the two others are secondarily derived. Triangular spines never occur in the ACANTHARIA, whilst, however, they are common in the #Sphærellaria#. The first and original form, the cylindrical spine, is either a true cylinder of equal thickness in its whole length, or it is more or less conical. Rarely the spine is in the distal half spindle-shaped, and thicker than in the basal half. The second form, the two-edged spine, is more or less compressed from two opposite sides; its two edges are either more blunt, rounded, or more acute, sharp; its transverse section in the former case is elliptical, in the latter case lanceolate or rhomboidal. Sometimes the two edges are broader and in the form of two thin opposite wings. The two-edged spines may be occasionally shorter, triangular or lanceolate, at other times longer sword-shaped or linear. The third form, the four-edged spine, has constantly a square transverse section; the sides of this square are either even or concave; in the latter case the four edges are broadened and wing-like, but in the former case not. The quadrangular spines are either prismatic (of equal breadth throughout their whole length) or pyramidal (becoming gradually thinner towards the distal apex).

The Apex of the Radial Spines, or their free distal end, is in the majority of ACANTHARIA simple, conical. In the minority it is either truncated or bifid, or four-sided pyramidal, often with two, rarely with four prominent parallel teeth. In some forms {723}the bifid spines are so deeply cleft that they become forked. Much more interesting and more varied than these different forms of the distal end are those of the apophyses of the radial spines.

The Apophyses of the Radial Spines, or their "lateral transverse processes," are of the greatest importance for the morphological development of the whole subclass. Only in sixteen among the sixty-five genera of ACANTHARIA are the apophyses perfectly wanting; in the other genera they determine in the first place their general character. In the #Acanthometra# the apophyses remain perfectly free, whilst in the #Acanthophracta# their meeting ends or branches compose the latticed shell. All differences in form and shape of the apophyses can be reduced to only two primary modes; either the spine bears two opposite or four crossed apophyses; correspondingly all Acantharia apophysaria may be divided into two different main groups, the Zygapophysica (with two opposite lateral processes) and the Staurapophysica (with four crossed lateral processes opposite in pairs). Both groups have probably no direct phylogenetic connection, but seem to be derived independently from different stocks, and produce different families. The Zygapophysica are probably derived from Astrolonchida with two-edged spines (Zygacantha), and from this group arise the Diporaspida, the ancestral group of the majority of #Acanthophracta#. On the other hand the Staurapophysica are probably derived from Astrolonchida with four-edged spines (Acanthonia), and from this group arise the Tessaraspida. The apophyses of the #Acanthonida# are partly simple, partly branched or even latticed; the apophyses of the #Acanthophracta# are never simple, constantly branched and commonly latticed.

The Malacoma (or the whole soft body of the ACANTHARIA as opposed to the skeleton) exhibits some peculiarities which distinguish them from the other Radiolaria, as well in the structure of the central capsule and its nucleus as in that of the enveloping extracapsular body and the pseudopodia.

The Central Capsule is constantly spherical in the far greater number of the ACANTHARIA, viz., in the following six families:--Astrolophida, Chiastolida, Astrolonchida, Dorataspida, Sphærocapsida, and Phractopeltida. Among these six families the Astrolonchida and Dorataspida are far greater and far richer in different forms than all the other families. The central capsule becomes ellipsoidal or cylindrical, prolonged in one axis, in the three families, Amphilonchida, Belonapsida, and Diploconida; it becomes discoidal or lenticular, by the shortening of one axis, in two families, viz., in the Quadrilonchida and Hexalaspida. Finally, the peculiar family Litholophida is distinguished by the conical form of its central capsule.

The Membrane of the central capsule in all ACANTHARIA is simple, commonly thin, sometimes very delicate; in some species it seems to be developed late, just immediately before the formation of the spores; but in no species is it completely missing. The membrane is constantly pierced by innumerable fine pores, for the emission of the {724}pseudopodia; but in many species (and probably more or less in all ACANTHARIA) there is recognisable a certain regularity in the disposition of the numerous pseudopodia and of the pores by which they radiate from the capsule. Sometimes these pores are disposed in a regular network of ramified lines, whilst the meshes of this network are devoid of pores; in other cases they form regular tufts or bushes between the radial spines. Probably in no ACANTHARIA are the pores of the capsule membrane so numerous and so equally distributed throughout as in the SPUMELLARIA; we may therefore call the former ACTIPYLEA (in opposition to the latter, as PERIPYLEA).

The Nucleus of the ACANTHARIA is constantly excentric, whilst it is originally constantly central in the SPUMELLARIA. This excentric position is a necessary consequence of the centrogenous development of the radial spines. Probably connected with this peculiarity is the other, that the nucleus assumes a peculiar, complicated structure, and that in the greater number of ACANTHARIA it becomes cleft very early, and that this cleavage is effected by a peculiar kind of gemmation, first detected and very accurately described by R. Hertwig (compare his Organismus d. Radiol., 1879, pp. 10-24). However, in the young ACANTHARIA the nucleus is constantly simple, and in a certain number of species its cleavage takes place late (as in the greater number of SPUMELLARIA).

The Endoplasm, or the intracapsular sarcode, exhibits in the greater number of ACANTHARIA a more or less distinct radial arrangement; but this is often concealed by the different enclosed products of the endoplasm--oil-globules, vacuoles, red or different coloured pigment-granules, crystals, &c. Often it encloses a variable number of "yellow cells" (becoming green by mineral acids) to be considered as symbiotic xanthellæ.

The Calymma or the jelly-veil, including the central capsule, in the ACANTHARIA is more or less voluminous, and commonly envelops the skeleton perfectly. In its surface is sometimes developed a peculiar network of "supporting fibres." A very peculiar product are the remarkable "Myophrisca" of the #Acanthometra#, which are wanting in the #Acanthophracta#; they were first detected by Johannes Müller, and figured as "Cilien-Kränze," afterwards explained by Hertwig as "contractile Fäden," similar to muscular fibrillæ (compare below).

The Matrix, placed between the calymma and central capsule, in the majority of the ACANTHARIA is a rather thin layer of granular exoplasm.

The Pseudopodia arising from it are not so numerous as in the SPUMELLARIA, and not so equally disposed over the whole surface. Also their tendency to ramify, anastomose, and form networks seems to be much less developed. Commonly they are simple or little ramified. In many cases (and perhaps everywhere) there may be distinguished two different kinds of pseudopodia:--(1) Axopodia, or permanent pseudopodia (with axial filaments?), piercing the wall of the central capsule, and arising from the central mass of endoplasm; and (2) Collopodia, or variable pseudopodia (without axial filaments), arising outside the capsule from the matrix of extracapsular sarcode or from the {725}exoplasm on the surface of the calymma. These and other differentiations seem to indicate that the pseudopodia in the ACANTHARIA are more highly developed than in the SPUMELLARIA, and justify the denomination of the former as "Actipylea."

Synopsis of the Orders and Suborders of ACANTHARIA.

------------------------------------------------------------------------- I. ACANTHOMETRA. Skeleton composed only of acanthinic radial spines not forming a complete lattice-shell. ------------------------------------------------------------------------- Radial spines in variable and indefinite number, disposed irregularly, 1. #Actinelida#.

Radial spines constantly twenty, disposed regularly after the Müllerian law of Icosacantha, 2. #Acanthonida#. ------------------------------------------------------------------------- II. ACANTHOPHRACTA. Skeleton composed of twenty acanthinic radial spines (disposed after the Müllerian law) and of a spherical or variously shaped complete lattice-shell. ------------------------------------------------------------------------- Radial spines all twenty of equal size; shell and central capsule spherical, 3. #Sphærophracta#.

Radial spines of different sizes; shell and central capsule ellipsoidal, discoidal, or heteromorphous, 4. #Prunophracta#.

----

Order III. ACANTHOMETRA, Johannes Müller, 1855.

Acanthometra, J. Müller, 1855, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin. Acanthometrida, Haeckel, 1862, Monogr. d. Radiol., p. 371. Acanthometrea, R. Hertwig, 1879, Organismus d. Radiol., p. 133. Acanthonida et Litholophida, Haeckel, 1881, Prodromus, pp. 465, 469.

Definition.--ACANTHARIA without complete latticed shell.

The order #Acanthometra#, the third order of Radiolaria, comprises all those ACANTHARIA in which the acanthinic skeleton is only composed of radial spines arising from one common central point, but never forms a complete latticed shell. By the absence of such a latticed or fenestrated shell the #Acanthometra# differ principally from the nearly allied #Acanthophracta#, the second order of ACANTHARIA, which constantly possess such a complete shell.

Johannes Müller, who first detected and described the #Acanthometra# (in 1855, loc. cit.), defined them as follows:--"Radiolaria without shell, with siliceous radial spines" (1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 46). He described and figured eighteen species of them, disposed in four genera (Acanthometra with fifteen species, and Zygacantha, Lithophyllium, Lithoptera, each with a single species). Among those eighteen species, however, were two "Acanthometræ cataphractæ," appertaining to the following order, the #Acanthophracta#.

In my Monograph (1862, p. 371) all true #Acanthometra# were united into a single family, Acanthometrida, with the following definition:--"Skeleton composed of a number of radial spines, piercing the central capsule and united in its centre, without {726}latticed shell." In the majority of them I observed that the skeleton did not consist of silex, but of a very peculiar organic substance, which I called "acanthin." At that time I divided the family Acanthometrida into four subfamilies:--(1) Acanthostaurida, (2) Astrolithida, (3) Litholophida, (4) Acanthochiasmida. The two former now represent the suborder #Acanthonida#, the two latter the suborder #Actinelida#. The number of genera which I distinguished in my Monograph amounted to nine, the number of species to fifty. By the rich collections of the Challenger this number is so much increased that we can here describe twenty-seven genera and one hundred and sixty species.

Richard Hertwig in his work on the Organismus der Radiolarien (1879, pp. 6-25) adopted my family Acanthometrida, and gave a very accurate description of its anatomical structure. He confirmed my observations that the radial spines of this family are never hollow, but solid, and that their chemical substance is not silex, but the organic matter "acanthin." He found that the simple nucleus of the Acanthometrida is commonly very early cleft, and that the peculiar brushes of filaments on the calymma, described by Johannes Müller and by me as "Gallert-cilien," are peculiar "contractile filaments," comparable to the "muscle-fibrillæ" of some Infusoria, or the "Myophan-filaments" (Myophrisca).

The order #Acanthometra# is here divided into two different suborders of very unequal extent and value, the #Actinelida# and #Acanthonida#. The first may be regarded as the common ancestral stock, not only of the second, but of all ACANTHARIA. In the small group of #Actinelida# the number of radial spines is variable and commonly indefinite, often very large (more than a hundred); they are therefore Adelacantha. The second suborder, the #Acanthonida#, comprise by far the greatest part of the order, and possess constantly twenty radial spines, regularly disposed after the Müllerian law; they are therefore (like all #Acanthophracta#) Icosacantha (compare above, p. 717).

The #Actinelida# possess constantly simple radial spines, without any apophyses; their form is commonly very simple and primitive. This suborder comprises three small but very different families, the Astrolophida, Litholophida, and Chiastolida. The first family, the Astrolophida, is the original ancestral group. A large and variable, commonly indefinite number of radial spines is here united in the centre of the spherical central capsule and radiating within a spherical space. In the second family, the Litholophida, a small and variable number of radial spines (between ten and twenty) is united in the apex of a conical central capsule and radiating within the quadrant or octant of a spherical space. In the third family, the Chiastolida, a variable number of radial spines is grown together by pairs, in such a manner that every two opposite spines (placed originally in one axis of the spherical central capsule) forms a single "diametral spine"; all these diametral spines are not united in the centre of the central capsule but only crossed loosely near the centre.

{727}The #Acanthonida#, the second suborder of #Acanthometra#, embraces by far the greatest number in this order, viz., all those forms in which twenty radial spines are regularly disposed after the Müllerian law--Icosacantha (compare above, p. 717). The radial spines of this suborder are either simple or provided with transverse processes (either two opposite or four crossed apophyses). They are commonly united in the middle of the central capsule by their opposed basal ends, forming small pyramids; the meeting triangular faces of the neighbouring pyramids being propped one upon another. Above these small basal pyramids often arises a basal leaf-cross formed by four broad triangular leaves or wings with straight edges; the meeting thin edges of the neighbouring spines serve for strengthening the basal junction and form hollow pyramidal spaces or compartments, filled with the contents of the central capsule (compare p. 721). The suborder #Acanthonida# comprises three different families, the Astrolonchida, Quadrilonchida, and Amphilonchida. The first family, the Astrolonchida, comprises by far the greater number of the #Acanthonida#; those genera in which all twenty spines are perfectly equal or nearly equal in size and form. In the second family, the Quadrilonchida, the four equatorial spines are much larger (and often also of another form) than the sixteen other spines (often also the eight tropical larger than the eight polar spines). The third family, the Amphilonchida, is distinguished by the preponderating development of only two opposite equatorial spines, which are much larger (and often also of another form) than the eighteen other spines.

Synopsis of the Suborders and Families of #Acanthometra#.

------------------------------------------------------------------------- Suborder I. ACTINELIDA. Number of the radial spines variable, either more or less than twenty, commonly disposed irregularly and not according to the Müllerian law. ------------------------------------------------------------------------- Radial spines very numerous (thirty to a hundred or more), radiating from a common centre within a spherical space, 1. ASTROLOPHIDA.

Radial spines between ten and twenty, radiating from one common point within a sphere-quadrant, 2. LITHOLOPHIDA.

Radial spines of variable number; every two opposite spines grown together in the centre; therefore numerous diametral spines are crossed freely in the centre, 3. CHIASTOLIDA. ------------------------------------------------------------------------- Suborder II. ACANTHONIDA. Number of the radial spines constantly twenty, disposed regularly according to the Müllerian law. ------------------------------------------------------------------------- All twenty radial spines nearly equal, and of the same size and form, 4. ASTROLONCHIDA.

Four equatorial spines much larger than (and often also of different form from) the sixteen other spines, 5. QUADRILONCHIDA.

Two opposite equatorial spines (or principal spines) much larger than (and often also of different form from) the eighteen other spines, 6. AMPHILONCHIDA.

{728}----

Suborder I. ACTINELIDA, Haeckel, 1882.

Definition.--#Acanthometra# with a variable number of radial spines, which are commonly irregularly disposed, not according to the Icosacantha.

Family XXXIII. #ASTROLOPHIDA#, Haeckel.

Astrolophida, Haeckel, 1881, Prodromus, p. 469.

Definition.--#Acantharia# with a variable number of simple radial spines, radiating within a spherical space from one common central point which is the centre of the spherical central capsule. No lattice shell.

The family #Astrolophida# comprises the simplest and the most primitive forms among all ACANTHARIA, and may therefore be regarded as the common ancestral stock of this whole legion or subclass of Radiolaria. The acanthinic skeleton is composed of a variable number of quite simple radial spines, which are united in the centre of the spherical central capsule and radiate, piercing its walls and the surrounding jelly-veil, within a spherical space.

The first observed form of this family is the ancestral genus Actinelius, two different species of which I detected in 1864 in the northern Mediterranean, at Villafranca, near Nice (compare Zeitschr. f. wiss. Zool., 1865, Bd. xv. p. 364, Taf. xxvi. fig. 4). Three other species of the same genus were afterwards found by me in the Challenger collections. Whilst in this Actinelius all radial spines are of the same size, a new nearly allied genus, Astrolophus (with two species), differs from it by the different size of the radial spines, a small number of very large spines being intermingled with a very large number of small spines. In these two genera, Actinelius and Astrolophus (the true "Astrolophida" sensu strictiori), the number of the radial spines is quite indeterminable and their arrangement quite irregular and variable.

A third remarkable genus, Actinastrum, differs from these two genera in the definite number and regular order of thirty-two radial spines, and may therefore perhaps better represent a peculiar family, Actinastrida. In this genus (of which two species were observed) the thirty-two radial spines are disposed in such a regular manner that they lie in four meridian planes, and that their distal ends fall into five parallel zones. These five zones and these four planes are the same as we find in all Icosacantha (compare above, p. 717). Also the constant twenty spines of these latter are present in Actinastrum; but their number is here enlarged by twelve other spines missing in the Icosacantha; four of these are secondary or interradial equatorial spines, lying opposite in pairs between the four primary or perradial equatorial spines; and eight are perradial tropical spines, lying between the eight interradial tropical spines. Therefore the {729}distal ends of the thirty-two radial spines are disposed regularly in five parallel zones, and while two zones (the two polar) contain only the points of every four spines, three zones (the single equatorial and the two tropical) contain the points of every eight spines. The four meridian planes are in Actinastrum the same as in the Icosacantha, crossed in the spineless axis at angles of 45°. But in the Icosacantha each of the two perradial meridian planes contains six radial spines (two equatorial and four polar), each of the two interradial meridian planes only four tropical spines. Whereas in Actinastrum each of the two primary or perradial meridian planes contains ten spines (two equatorial, four tropical, and four polar), each of the two secondary or interradial meridian planes six spines (two equatorial and four tropical). We find therefore altogether thirty-two radial spines in three orders; eight equatorial, sixteen tropical, and eight polar spines.

Only one other genus of Radiolaria exhibits the same characteristic disposition of thirty-two radial spines as Actinastrum, and this is Chiastolus; but here the two opposite spines of each pair are grown together and form one diametral spine; and the sixteen diametral spines are crossed in the centre of the capsule. In Actinastrum, as in Astrolophus and Actinelius, the central ends or bases of all the spines are pyramidal, and the triangular faces of the neighbouring spines rest one upon another (as in the greater number of #Acanthonida#). The form of the radial spines in all Astrolophida is quite simple, without lateral processes or apophyses; chiefly cylindrical, more rarely compressed, two-edged or quadrangular.

The central capsule in all Astrolophida is spherical, and in the younger specimens contains a single large concentric and lobed nucleus, but in the older specimens a large number of small nuclei. The surrounding jelly-veil or calymma seems commonly to envelop the spines perfectly. The piercing pseudopodia radiate everywhere between the spines, and are very numerous and thin. The circulating granules in them are sometimes red (Actinelius purpureus).

Synopsis of the Genera of Astrolophida.

Radial spines of indefinite {Spines of equal size, 317. Actinelius. number and of irregular { disposition. {Spines of unequal size, 318. Astrolophus.

Radial spines thirty-two, disposed regularly in five parallel zones, 319. Actinastrum.

Genus 317. Actinelius,[357] Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 364.

Definition.--#Astrolophida# with a variable and undetermined number of simple radial spines, all of equal size, united in the centre of the spherical central capsule.

{730}The genus Actinelius comprises the most simple and primitive forms among all ACANTHARIA, and may be regarded as the common ancestral stock of this whole legion. The spherical central capsule is pierced by numerous simple radial spines of equal size, the pyramidal bases of which are supported one upon another with their triangular faces in the centre of the capsule. The number and position of the spines are quite indefinite and variable. We may derive Actinelius either from Actissa (#Colloidea#) by development of acanthinic radial spines, or directly from Actinosphærium (Heliozoa) by formation of a central capsule.

Subgenus 1. Actinelarium, Haeckel.

Definition.--Radial spines cylindrical, conical, or spindle-shaped, their transverse section circular.

1. Actinelius primordialis, n. sp. (Pl. 129, fig. 1).

Spines sixty to eighty or more, cylindrical, at the distal end thickened, spindle-shaped. Apex simple. Base a small slender pyramid. Central capsule yellow. Granules of the sarcode colourless.

Dimensions.--Length of the spines 0.3 to 0.4, breadth in the distal part 0.02, in the basal part 0.008.

Habitat.--Central Pacific, Stations 265 to 274, surface.

2. Actinelius purpureus, Haeckel.

Actinelius purpureus, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 364, Taf. xxvi. fig. 4.

Spines thirty to forty or more, cylindrical, very thin, a little thinner towards both ends. Apex simple. Base a small sulcate pyramid. Central capsule opaque, purple. Granules of the sarcode also purple.

Dimensions.--Length of the spines 0.2 to 0.3, breadth 0.002.

Habitat.--Mediterranean (Nice), Haeckel.

Subgenus 2. Actinelidium, Haeckel.

Definition.--Radial spines compressed, two-edged; their transverse section elliptical or lanceolate.

3. Actinelius protogenes, n. sp.

Spines fifty to sixty, compressed, two-edged, gradually broadened towards the truncated distal end. Basal or proximal end thin, pyramidal. The spines of this species are similar to those of {731}Actinastrum pentazonium (p. 733) and of Chiastolus amphicopium (Pl. 129, fig. 3), but much more numerous, smaller, and not regularly disposed. These latter two Actinelida must be separated on account of the regular disposition of the thirty-two spines.

Dimensions.--Length of the spines 0.2, basal breadth 0.008, distal breadth 0.02.

Habitat.--South Pacific, Station 165, surface.

Subgenus 3. Actinelonium, Haeckel.

Definition.--Radial spines quadrangular, prismatic, or pyramidal, their transverse section square.

4. Actinelius pallidus, Haeckel.

Actinelius pallidus, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 364.

Spines eighty to one hundred and twenty or more, quadrangular, prismatic, of equal breadth throughout their whole length. Apex simple, truncate or pyramidal. Base a four-sided slender pyramid. Central capsule pale yellowish. Granules of the sarcode colourless.

Dimensions.--Length of the spines 0.2 to 0.3, breadth 0.005.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific.

5. Actinelius polyacanthus, n. sp.

Spines two hundred to three hundred or more, quadrangular, pyramidal, gradually thinned towards the simple apex. Base a small three-sided pyramid. Central capsule opaque.

Dimensions.--Length of the spines 0.12 to 0.18, basal breadth 0.012.

Habitat.--South Pacific, Station 291, surface.

Genus 318. Astrolophus,[358] Haeckel, 1881, Prodromus, p. 469.

Definition.--#Astrolophida# with a variable and undetermined number of simple radial spines of different sizes (large and small spines intermingled), which are united in the centre of the spherical central capsule.

The genus Astrolophus differs from the nearly allied ancestral genus Actinelius only in the unequal size of the numerous radial spines. In both observed species very numerous small spines are intermingled with a small number of large spines, and between them numerous spines of medium size. The small spines fill up the hollow spaces between the basal parts of the large spines.

{732}1. Astrolophus stellaris, n. sp.

Radial spines from one hundred to two hundred, of very different sizes, but of similar form; about sixteen to twenty very large spines, forty to fifty of medium size, and one hundred to one hundred and twenty much smaller. All spines cylindrical in the greater part of their length, with simple apex, gradually thickened towards the central part, conical, without edges. The base itself is a slender pyramid with four to eight edges.

Dimensions.--Length of the largest spines 0.3 to 0.4, of the majority 0.1 to 0.2, of the smallest 0.05 to 0.1.

Habitat.--South Pacific, Station 288, surface.

2. Astrolophus solaris, n. sp. (Pl. 132, figs. 12_a_, 12_b_).

Radial spines from two hundred to three hundred, of very different sizes, but of similar form; about twenty to thirty very large spines, sixty to eighty of medium size, and one hundred and twenty to one hundred and fifty much smaller. All spines cylindrical in the greater part of their length, with simple apex, gradually thickened and four-edged towards the central base. The base itself is a slender pyramid with four to eight edges; partly the faces, partly the edges of these basal pyramids rest one upon another, the points of the larger spines meeting in the centre.

Dimensions.--Length of the largest spines 0.4 to 0.5, of the majority 0.2 to 0.3, of the smallest 0.1 to 0.16; basal thickness of the largest spines 0.015.

Habitat.--South-east Pacific (off Juan Fernandez), Station 296, surface.

Genus 319. Actinastrum,[359] n. gen.

Definition.--#Astrolophida# with thirty-two simple radial spines, regularly disposed within four meridian planes in such an order that their distal ends fall into five parallel zones. Central ends of the thirty-two spines supported one upon another in the centre of the spherical central capsule.

The genus Actinastrum differs from the two preceding genera in the definite number and order of the thirty-two radial spines, which are disposed in a very remarkable manner. Twenty radial spines are disposed after the Müllerian law of Icosacantha (compare above, p. 717). The remaining twelve spines are four equatorial spines lying in the two secondary meridian planes, and eight tropical spines lying in the two primary meridian planes. We have therefore together eight equatorial, sixteen tropical, and eight polar spines (compare above, p. 729).

{733}1. Actinastrum legitimum, n. sp.

All thirty-two radial spines of equal size and similar form, cylindrical, conical at the distal end, at the central base pyramidal. Central capsule pellucid, colourless.

Dimensions.--Length of the radial spines 0.3, breadth 0.004.

Habitat.--South Pacific, Station 288, surface.

2. Actinastrum pentazonium, n. sp.

All thirty-two radial spines of equal size and similar form, compressed, two-edged, gradually becoming broader and thinner from the pyramidal central base towards the truncated distal end. Central capsule dark, opaque. (Compare the similar Chiastolus amphicopium, Pl. 129, fig. 3.)

Dimensions.--Length of the radial spines 0.2, breadth at the base 0.005, at the distal end 0.02.

Habitat.--South Pacific (west coast of Patagonia), Station 302, surface.

Family XXXIV. LITHOLOPHIDA, Haeckel.

Litholophida, Haeckel, 1862, Monogr. d. Radiol., p. 401.

Definition.--ACANTHARIA with a variable number of simple radial spines radiating within a conical space (or within the quadrant of a sphere) from one common central point, which is the apex of the conical central capsule. No lattice-shell.

The family #Litholophida#, represented only by a single genus, Litholophus, differs from all other ACANTHARIA in the remarkable fact that the common point, from which the radial spines arise, is not the geometrical central point of the whole body, but is quite excentric in position, the apex of the conical or pyramidal central capsule. Therefore the spines form together a kind of brush or broom.

When I founded the family Litholophida in my Monograph (1862, p. 401) I knew only a single species, Litholophus rhipidium, observed very frequently in Messina. Another species, Litholophus ligurinus, was afterwards (1864) found by me at Nice. Six other species were detected in the preparations of the Challenger, some of them very frequent. All these eight species of Litholophus are very nearly allied, and exhibit only slight differences in the form and number of the radial spines; their mode of excentric connection and the structure of the peculiar soft body is everywhere the same.

The radial spines in all observed Litholophida possess the form of the genus Acanthonia, i.e., they are quite simple, four-sided prismatic or quadrangular, with square transverse section; their four edges are sometimes smooth, at other times elegantly denticulate, commonly more or less prominent or wing-shaped. In the greater number of species they are very long and of nearly equal breadth, prismatic; in some species they are more pyramidal, thinned towards the distal end; the latter {734}is commonly truncated or broken off, sometimes pyramidal. The central end is everywhere thinned, more or less pyramidal, and the neighbouring spines are propped one upon another by the triangular faces of their small basal pyramids. A slight pressure is sufficient to destroy their connection.

The number and disposition of the radial spines seem to be variable and irregular, but require further researches. In four of the observed eight species I found constantly ten spines, in two other species from ten to twenty (commonly twelve or sixteen), and in two species twenty or more. A certain order or disposition of the spines within the conical space in which they radiate could nowhere be ascertained.

When I first observed Litholophus, I supposed that it might only be a mutilated or altered form of an Acanthonia. Afterwards, observing many specimens with ten spines, I was led to the suggestion that they were produced by self-division of an Acanthonia, and that the number of the spines in each half of the body might be afterwards doubled. But this suggestion seems to be refuted by the fact that in no other genus of the numerous ACANTHARIA is self-division observed, and that many hundreds of Litholophus which I observed exhibit quite constantly only a single form of radial spines, that of Acanthonia--simple quadrangular spines without any apophyses.

Genus 320. Litholophus,[360] Haeckel, 1862, Monogr. d. Radiol., p. 401.

Definition.--#Litholophida# with a variable number of quadrangular diverging radial spines, united with pyramidal bases in the apex of the conical central capsule.

The genus Litholophus, the only one of this family, exhibits the peculiarities just described, but might more nearly be defined as a typical "genus" by the quadrangular form of the radial spines, identical with those of Acanthonia.

The central capsule of Litholophus is constantly conical or pyramidal, commonly opaque, of a dark brownish or reddish colour; it contains many small nuclei. It envelops the basal half of all radial spines in such a manner that their basal parts are united in its apex, and their distal parts pierce the rounded base of the conical capsule (Pl. 129, fig. 2).

The calymma or the jelly envelope of the central capsule is only developed at its base, where the spines radiate; at the conical mantle of the capsule it is very thin. The spines seem to be perfectly enclosed in the calymma and connected with it by the same contractile retinacula or "myophrisca" which we observe in the #Acanthonida#. The pseudopodia arise only from the rounded base of the conical capsule, and radiate between the spines, piercing the calymma, diverging within the conical space occupied by the fascicle of spines.

{735}Subgenus 1. Litholopharium, Haeckel.

Definition.--Ten radial spines.

1. Litholophus decimalis, n. sp.

Ten radial spines, four-sided prismatic, with prominent smooth edges, of equal breadth throughout their whole length.

Dimensions.--Length of the spines 0.2 to 0.3, breadth 0.006.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

2. Litholophus pyramidalis, n. sp.

Ten radial spines, four-sided pyramidal, with prominent smooth edges, gradually thickened from the small pyramidal base towards the truncated distal end.

Dimensions.--Length of the spines 0.3 to 0.4, breadth in the basal part 0.002, in the middle part 0.006, in the distal part 0.012 to 0.02.

Habitat.--Central Pacific, Station 266, surface.

3. Litholophus decapristis, n. sp. (Pl. 129, fig. 2).

Ten radial spines, four-sided prismatic, with prominent, elegantly denticulated edges, of equal breadth in their whole length.

Dimensions.--Length of the spines 0.2 to 0.4, breadth 0.008.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

4. Litholophus decastylus, n. sp.

Ten radial spines, four-winged pyramidal, with broad and thin, elegantly denticulated edges, gradually thickened from the small pyramidal base towards the truncated distal end.

Dimensions.--Length of the spines 0.2 to 0.3, breadth in the basal part 0.002, in the middle part 0.005, in the distal part 0.015.

Habitat.--South Atlantic, Station 332, surface.

Subgenus 2. Litholophidium, Haeckel.

Definition.--Number of the radial spines variable, between ten and twenty, commonly twelve to sixteen.

{736}5. Litholophus ligurinus, Haeckel.

Litholophus ligurinus, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 366.

Spines of variable number, from eleven to twenty, commonly twelve to sixteen, four-sided prismatic, with smooth thin edges, of equal breadth in their whole length or a little thinner towards the proximal end.

Dimensions.--Length of the spines 0.3, breadth 0.005.

Habitat.--Mediterranean (Nice); Central Pacific, Station 274, surface.

6. Litholophus rhipidium, Haeckel.

Litholophus rhipidium, Haeckel, 1862, Monogr. d. Radiol., p. 402, Taf. xix. fig. 6.

Spines of variable number, from eleven to twenty, commonly twelve to sixteen, four-sided prismatic, with distantly denticulated edges, of equal breadth in their whole length or a little thinner towards both ends.

Dimensions.--Length of the spines 0.3, breadth 0.006.

Habitat.--Mediterranean (Messina); North Atlantic, Station 352, surface.

Subgenus 3. Litholophonium, Haeckel.

Definition.--Number of the radial spines twenty (or more?).

7. Litholophus fasciculus, n. sp.

Spines constantly (?) twenty, four-sided prismatic, with smooth prominent edges, nearly of equal breadth throughout their whole length.

Dimensions.--Length of the spines 0.3 to 0.5, breadth 0.008.

Habitat.--South Pacific, Station 291, surface.

8. Litholophus penicillus, n. sp.

Spines constantly twenty (or more?), four-sided prismatic, with distantly denticulated edges, gradually thickened from the small pyramidal base to the middle part, of equal breadth in the distal half.

Dimensions.--Length of the spines 0.3 to 0.4, breadth 0.005 to 0.007.

Habitat.--North Pacific, Station 252, surface.

Family XXXV. #CHIASTOLIDA#, Haeckel.

Acanthochiasmida, Haeckel, 1862, Monogr. d. Radiol., p. 402.

Definition.--ACANTHARIA with a variable number of simple radial spines, which are grown together in pairs (two opposite spines of each pair representing together a single diametral spine). Diametral spines crossed loosely in the centre of the spherical or irregular roundish central capsule. No lattice-shell.

{737}The family #Chiastolida# (or Acanthochiasmida) differs from all other ACANTHARIA in the peculiar mode of the radial spines; these grown together in pairs in the centre of the body, so that every two spines opposite in one axis of the body form together one single diametral spine. All diametral spines are loosely crossed in the middle of the central capsule, or connected by a peculiar screw-like winding, but not united firmly.

I established the family Acanthochiasmida in my Monograph (1862, p. 402) upon the single genus Acanthochiasma (with three species), in which only ten diametral spines are constantly found; I derived these from the twenty radial spines of the common #Acanthometra#, supposing that every two opposite spines of the latter (lying in one axis) were grown together in the centre, whilst the intimate connection of the twenty radial spines in the common centre was dissolved. This opinion was afterwards confirmed by Richard Hertwig, who observed Acanthochiasma intact in the living state. Although two species of this genus are cosmopolitan and very common, the number of species is very small; I could add to those three older known forms only a single new species.

Another genus of this family, Chiastolus, was observed by me only in a single specimen but it is extremely interesting. It has sixteen diametral spines, disposed quite regularly after the same law of the thirty-two spines of Actinastrum which we described above (compare above, p. 729). Therefore we cannot doubt that the former is derived from the latter in the same way, every two opposite radial spines (of one axis) being grown together to form a single diametral spine. As we place Acanthometron (with twenty spines) and Actinastrum (with thirty-two spines) in two different families, it would perhaps be more convenient to separate also Acanthochiasma and Chiastolus as representatives of two different families--Acanthochiasmida (with ten diametral spines) and Chiastolida (with sixteen diametral spines).

As we derive Acanthochiasma from Acanthometron by concrescence in pairs of the twenty radial spines, the Müllerian law of Icosacantha must be employed also to the ten diametral spines of the former, therefore two of them are equatorial, four tropical, and four polar spines. In the same way we may employ the new law of disposition found in the thirty-two radial spines of Actinastrum equally to the sixteen diametral spines of Chiastolus, which we derive from the former, four of them are equatorial, eight tropical, and four polar spines (compare above, p. 732).

The Central Capsule of the Chiastolida is spherical, and exhibits in general the same shape as in the #Acanthonida#, and specially in the Astrolonchida. Of course every diametral spine pierces the capsule twice, at two points diametrically opposed. In some species of Acanthochiasma the central capsule is formed very late, so that it seems often to be absent. A very accurate description of the capsule and its nucleus, as well as of the calymma and the pseudopodia, is given by Richard Hertwig in his Organismus der Radiolarien (1879, pp. 10-18). The pseudopodia are very numerous, and sometimes bear reddish granules.

{738}Synopsis of the Genera of Chiastolida.

I. Subfamily Chiastolidina. Sixteen diametral spines, derived by concrescence of thirty-two radial spines, 321. Chiastolus.

II. Subfamily Acanthochiasmida. Ten diametral spines, derived by concrescence of twenty radial spines, 322. Acanthochiasma.

Genus 321. Chiastolus,[361] n. gen.

Definition.--#Chiastolida# with sixteen diametral spines, derived from thirty-two radial spines opposite and grown together in pairs.

The genus Chiastolus, hitherto known only by a single observed specimen, comprises the Chiastolida with sixteen diametral spines, which are loosely crossed in the centre of the body. Four of these spines are equatorial, four polar, and eight tropical. We derive Chiastolus from Actinastrum by concrescence of every two opposite spines in one axis of the body (compare above, pp. 729, 732).

1. Chiastolus amphicopium, n. sp. (Pl. 129, figs. 3, 3_a_, 3_b_).

Spines in the central part cylindrical, spirally convoluted in a very peculiar manner, broadened towards both ends, strongly compressed, two-edged; the broadest parts are the two truncated distal ends, five to seven times as broad as the thinnest central part, which is placed between two spindle-shaped intumescences. These cochleary central parts of the sixteen spines seem to be resting one upon another. Each spine (composed of two opposite equal radial spines) has nearly the form of a double oar. The single observed specimen (preserved in glycerine) exhibited a most regular disposition of the thirty-two spines (grown together in pairs in the centre). The diameter of the dark non-transparent spherical central capsule equalled one-fifth to one-fourth of the total length of the double spines. When the soft parts of the body were destroyed by sulphuric acid, the sixteen single spines were suddenly dispersed.

Dimensions.--Length of the sixteen double spines 0.5, distal breadth (of the truncated ends) 0.05, central breadth 0.01; diameter of the central capsule 0.12.

Habitat.--South-east Pacific (near Juan Fernandez), Station 297, surface.

Genus 322. Acanthochiasma,[362] Krohn, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 810.

Definition.--#Chiastolida# with ten diametral spines, derived from twenty radial spines opposite and grown together in pairs.

{739}The genus Acanthochiasma with a small number of common species, comprises the Chiastolida with ten diametral spines, which are loosely crossed in the centre of the body. I could distinguish only four species, two of which are cosmopolitan and very widely distributed. In all four species the diametral spines are quite simple, cylindrical; only in one species distinguished by a spiral winding or torsion in the middle part, where they are crossed one to another. We derive Acanthochiasma from Acanthometron by concrescence of every two spines opposite in one axis of the body.

1. Acanthochiasma krohnii, Haeckel.

Acanthochiasma krohnii, Haeckel, 1862, Monogr. d. Radiol., p.403, Taf. xix. fig. 7.

Acanthochiasma krohnii, R. Hertwig, 1879, Organismus d. Radiol., Taf. ii. fig. 6.

Spines needle-shaped, cylindrical, very thin and long, of equal breadth in their whole length, distinguished by a high degree of elasticity. Central capsule colourless or yellowish-white, transparent. Granules of the sarcode colourless.

Dimensions.--Length of the spines 0.5 to 1.0, breadth 0.001 to 0.002.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, very common.

2. Acanthochiasma rubescens, Krohn.

Acanthochiasma rubescens, Haeckel, 1862, Monogr. d. Radiol., p. 403.

Spines cylindrical, of equal breadth in their whole length, not very elastic, pointed at the two ends. Central capsule intransparent, reddish, with violin-shaped concretions. Granules of the sarcode red coloured.

Dimensions.--Length of the spines 0.2 to 0.6, breadth 0.004 to 0.006.

Habitat.--North Atlantic, Madeira, Krohn; Lanzerote, Haeckel.

3. Acanthochiasma fusiforme, Haeckel.

Acanthochiasma fusiforme, Haeckel, 1862, Monogr. d. Radiol., p. 404, Taf. xix. fig. 8.

Spines spindle-shaped, from the thicker central part thinned towards the two thin conical ends, perfectly straight and smooth, rigid, inelastic. Central capsule non-transparent, brown.

Dimensions.--Length of the spines 0.3 to 0.5, breadth in the central part 0.006 to 0.009.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific.

4. Acanthochiasma spirale, n. sp.

Spines spindle-shaped, tapering from the thicker central part towards the two thin conical ends, rigid, inelastic; their central part is spirally convoluted in a very peculiar cochlea-like manner, as in Chiastolus amphicopium (Pl. 129, figs. 3_a_, 3_b_). The ten spines are propped one upon another by the central screw. Central capsule dark, opaque.

Dimensions.--Length of the spines 0.2 to 0.3, breadth of the central spiral part 0.01.

Habitat.--Central Pacific, Station 266, surface.

{740}----

Suborder II. ACANTHONIDA, Haeckel (Pls. 130-132).

Acanthonida, Haeckel, 1881, Prodromus, p. 465.

Definition.--#Acanthometra# with twenty radial spines, disposed according to the Müllerian or Icosacanthan law in five zones each of four spines.

Family XXXVI. #ASTROLONCHIDA#, Haeckel (Pl. 130).

Astrolonchida, Haeckel, 1881, Prodromus, p. 465.

Definition.--#Acanthometra# with twenty radial spines of nearly equal size and similar form, disposed according to the law of the Icosacantha. No lattice-shell.

The family #Astrolonchida#, the first and oldest of the #Acanthonida#, is no doubt the ancestral stock not only of this suborder but also all #Acanthophracta#, i.e., of all Icosacantha or all ACANTHARIA in which twenty radial spines are regularly disposed according to the Müllerian law, forming five zones each of four alternating spines (compare above, p. 717). The Astrolonchida differ from the #Acanthophracta# in the absence of a complete lattice-shell, from the other two families of #Acanthonida# (the Quadrilonchida and Amphilonchida) in the equal size and similar form of all the spines. Probably this equality is nowhere quite perfect, since in all Icosacantha the central bases of the twenty spines exhibit originally certain slight differences of form and junction, effected by the regular disposition itself. But setting aside this slight difference, only recognisable by means of a very accurate investigation of the central junction (and in thinner spines often not at all recognisable), the twenty spines of the Astrolonchida appear perfectly equal. Therefore the four equatorial spines are not distinguished from the sixteen other spines, as is constantly the case in the two following families.

The number of genera (eleven) and of species (seventy-six) in the Astrolonchida is far larger than in the five other families of #Acanthometra#, and requires a distinction into three different subfamilies. (A) In the Zygacanthida the form of the radial spines is quite simple, without apophyses or transverse processes; (B) in the Phractacanthida each spine bears two opposite apophyses (rarely two longitudinal rows of these opposite apophyses); (C) in the Stauracanthida each spine bears a cross of four apophyses, opposite in pairs (rarely four longitudinal crossed rows of apophyses, opposite in pairs). The Phractacanthida and Stauracanthida appear as two divergent branches of the pedigree, derived independently from the common ancestral stock of Zygacanthida.

In the Zygacanthida, constantly devoid of apophyses, we can distinguish only three genera, characterised by the different fundamental form of the radial spines; these are:--(1) Acanthometron, with cylindrical or conical spines (without edges); (2) Zygacantha, with compressed and two-edged spines; (3) Acanthonia, with four-edged, prismatic or pyramidal spines. The transverse section of the spines is in the first case {741}circular, in the second elliptical or lanceolate, in the third square. All the different forms of spines, which we find in the numerous ACANTHARIA, may be reduced to these three forms, and among these the second and third are derived from the first.

The development of apophyses or of lateral transverse processes (wanting in the Zygacanthida) is of the greatest value for the further differentiation of the ACANTHARIA. For from the Phractacanthida (with two opposite apophyses on each spine) we must derive the Phrastaspida, the common ancestral stock of the Diporaspida (and therefore also the Belonaspida, Hexalaspida, Diploconida, and Phractopeltida). On the other hand the Stauracanthida (with four crossed apophyses on each spine) have produced the Stauraspida, or the ancestral group of the Tessaraspida and Sphærocapsida. From all these #Acanthophracta#, possessing a complete lattice-shell, the Astrolonchida differ in the absence of such a complete shell. Also in the few cases in which the apophyses become latticed (Doracantha among the Phractacanthida, and Phatnacantha among the Stauracanthida), the lattice-plates of the neighbouring spines never meet with their edges, as is the case in all #Acanthophracta#. But in a phylogenetic as well as in an ontogenetic sense the former are the ancestral stock of the latter.

The Central Capsule in the Astrolonchida is commonly spherical, sometimes with twenty roundish elevations or conical papillæ, extending radially to the basal half of the radial spines. The calymma is voluminous, and forms around the radial spines conical or cylindrical "jelly-sheaths," which are connected with the spines by coronas of Myophrisca (or of the bodies formerly called "Gallert-cilien," afterwards recognised as "contractile Filamente").

Synopsis of the Genera of Astrolonchida.

------------------------------------------------------------------------- I. Subfamily Zygacanthida. Twenty radial spines simple, without apophyses or lateral transverse processes. ------------------------------------------------------------------------- Spines cylindrical, with circular transverse section, 323. Acanthometron.

Spines compressed, two-edged or lamellar, with elliptical or rhomboidal transverse section, 324. Zygacantha.

Spines quadrangular (prismatic or pyramidal), with four edges, with square transverse section, 325. Acanthonia.

------------------------------------------------------------------------- II. Subfamily Phractacanthida. Twenty radial spines provided each with two opposite apophyses (or two longitudinal rows of apophyses). ------------------------------------------------------------------------- { Apophyses simple, 326. Lithophyllium. { Two apophyses opposite on { Apophyses branched, 327. Phractacantha. each spine. { { Apophyses latticed, 328. Doracantha.

Two opposite longitudinal rows of apophyses (four to eight or more apophyses on each spine, opposite in pairs), 329. Astrolonche. ------------------------------------------------------------------------- III. Subfamily Stauracanthida. Twenty radial spines provided each with four crossed apophyses (or four crossed longitudinal rows of apophyses). ------------------------------------------------------------------------- { Apophyses simple, 330. Xiphacantha. Four apophyses (in cross { form) opposite in pairs { Apophyses branched, 331. Stauracantha. on each spine. { { Apophyses latticed, 332. Phatnacantha.

Four longitudinal rows of apophyses, opposite in pairs in cross form on each spine, 333. Pristacantha.

{742}Subfamily 1. ZYGACANTHIDA, Haeckel.

Definition.--#Astrolonchida# with twenty simple radial spines, without apophyses or lateral transverse processes.

Genus 323. Acanthometron,[363] J. Müller, 1855, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 229.

Definition.--#Astrolonchida# with simple cylindrical or needle-shaped radial spines, without edges and without apophyses; their transverse section is circular.

The genus Acanthometron, with the restricted definition here given, is the most simple form of all #Acanthonida#, and may be regarded as the common ancestral form not only of this suborder but also of all #Acanthophracta#, in general of all Icosacantha, or all ACANTHARIA in which twenty radial spines are regularly disposed after the Müllerian law (p. 717). In the wider sense, given originally to #Acanthometra# by Johannes Müller, its discoverer, this genus comprised all ACANTHARIA constituting here our order "#Acanthometra#" (Radiolaria without lattice-shell, with radial spines united in the centre). In my Monograph (1862, p. 375) I restricted this genus to those "Acanthometrida" in which twenty simple spines of equal size (and without apophyses) are supported one upon another in the centre, and I separated as Astrolithium those forms in which they are grown together in the centre. But this difference now appears not so important, and I restrict here the genus Acanthometron (not #Acanthometra#) to those most simple forms in which the simple radial spines are cylindrical or conical, without edges.

Subgenus 1. Acanthometrella, Haeckel.

Definition.--Spines at the central base without leaf-cross, united by the opposed triangular faces of their pyramidal bases, resting one upon another.

1. Acanthometron elasticum, Haeckel.

Acanthometra elastica, Haeckel, 1862, Monogr. d. Radiol., p. 376, Taf. xv. fig. 1, Taf. xviii. fig. 1.

Acanthometra elastica, R. Hertwig, 1879, Organismus d. Radiol., Taf. i. figs. 2, 2_a_, 2_b_.

Spines cylindrical, very thin and long, needle-shaped, at the central base four-sided pyramidal, without leaf-cross. Distal apex conical. The spines are very elastic, of nearly equal thickness in their whole length. Central capsule quite pellucid, colourless, with a variable number of yellow pigment-bodies (xanthellæ?).

Dimensions.--Length of the spines 0.3 to 0.6, breadth 0.001 to 0.002.

Habitat.--Cosmopolitan, very common in all warmer seas; Mediterranean, Atlantic, Indian, Pacific, surface.

{743}2. Acanthometron cylindricum, n. sp. (Pl. 130, fig. 2).

Spines cylindrical, thick and long, at the central base thickened with a pear-shaped knob, and with very small central fulcral pyramid, without leaf-cross. Distal apex rounded or truncated. Central capsule opaque, filled with red pigment-bodies.

Dimensions.--Length of the spines 0.4 to 0.8, breadth 0.01 to 0.015.

Habitat.--Central Pacific, Stations 266 to 274, surface.

3. Acanthometron fuscum, J. Müller.

Acanthometra fusca, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 47, Taf. xi. fig. 4.

Acanthometra fusca, Haeckel, 1862, Monogr. d. Radiol, p. 377.

Spines very thin and long, in the proximal half cylindrical, in the distal half conical, gradually thinned towards the simple conical apex. Central base a small four-sided pyramid, without leaf-cross. Central capsule opaque, filled with brown pigment-bodies.

Dimensions.--Length of the spines 0.2 to 0.4, breadth 0.002 to 0.004.

Habitat.--Mediterranean (Cette, Portofino, Messina).

4. Acanthometron bulbosum, Haeckel.

Acanthometra bulbosa, Haeckel, 1862, Monogr. d. Radiol., p. 377, Taf. xv. fig. 2, Taf. xviii fig. 2.

Spines very thin and long, cylindrical, with simple needle-shaped apex; in the basal part conical, towards the centre much thickened, with a short four-sided fulcral pyramid, without leaf-cross. Central capsule opaque, filled with brown pigment-bodies.

Dimensions.--Length of the spines 0.3 to 0.5, breadth in the middle and outer part 0.001, in the basal part 0.008 to 0.012.

Habitat.--Mediterranean; Atlantic, Station 354, surface.

5. Acanthometron dolichoscion, Haeckel (Pl. 129, figs. 6-8).

Acanthometra dolichoscia, Haeckel, 1862, Monogr. d. Radiol., p. 377, Taf. xviii. figs. 3_a_, 3_b_.

Spines very long and thin, cylindrical, in the thickened outer half about twice as thick as in the thin inner half, at the simple apex compressed, two-edged. Central base little thickened, with a small four-sided pyramid, without leaf-cross. Central capsule transparent, whitish or yellowish.

Dimensions.--Length of the spines 0.6 to 0.8, breadth in the proximal part 0.004, in the distal part 0.008.

Habitat.--Mediterranean (Messina, Portofino), surface.

6. Acanthometron conicum, n. sp.

Spines short and thick, conical, gradually thinner from the thick conical base towards the simple apex. Central part of the base with a large fulcral pyramid, but without leaf-cross. Central capsule transparent, colourless (?).

Dimensions.--Length of the spines 0.08 to 0.12, basal breadth 0.02.

Habitat.--North Pacific, Station 244, surface.

{744}7. Acanthometron pellucidum, J. Müller.

Acanthometra pellucida, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 47, Taf. xi. figs. 1-3.

Acanthometra pellucida, Haeckel, 1862, Monogr. d. Radiol., p. 378.

Spines cylindrical, very thin and long, needle-shaped, nearly of equal thickness in their whole length. Central base with a small fulcral pyramid, without leaf-cross. Distal apex bifid or bifurcate, with two thin parallel teeth. Central capsule pellucid, colourless, with yellow pigment-bodies. (Differs from Acanthometron elasticum mainly in the bifid apex.)

Dimensions.--Length of the spine 0.1 to 0.3, breadth 0.002 to 0.004.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

8. Acanthometron wageneri, Haeckel.

Acanthometra wageneri, Haeckel, 1862, Monogr. d. Radiol., p. 378.

Spines cylindrical, in the thickened outer half about twice as broad as in the thin inner half. Central base a little thickened, with large fulcral pyramid, but without leaf-cross. Distal apex bifid, with two divergent, often denticulated teeth. Central capsule pellucid, with yellow pigment-bodies. (Differs from Acanthometron dolichoscion mainly in the bifid apex.)

Dimensions.--Length of the spines 0.2 to 0.5, breadth in the inner part 0.003, in the outer 0.006.

Habitat.--Adriatic Sea; Triest, Wagner; Corfu, Haeckel, surface.

Subgenus 2. Phyllostaurus, Haeckel, 1862, Monogr. d. Radiol., p. 381.

Definition.--Spines at the central base with a broad leaf-cross, composed of four prominent triangular lamellæ; the meeting edges of the neighbouring lamellæ are propped one upon another in such a manner that there are formed twenty-two hollow pyramidal spaces or compartments (compare p. 721).

9. Acanthometron siculum, Haeckel.

Acanthometra sicula, Haeckel, 1862, Monogr. d. Radiol., p. 382, Taf. xvii. figs. 1, 2; Taf. xviii. fig. 8.

Spines elongate, conical, tapering gradually from the thick base towards the simple distal apex. Conical circular base supported by a basal leaf-cross of double the breadth. Central capsule yellowish-brown, opaque.

Dimensions.--Length of the spines 0.3 to 0.4, basal breadth 0.008 to 0.012, leaf-cross 0.024.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

{745}10. Acanthometron catervatum, Haeckel.

Acanthometra brevispina, Haeckel, 1862, Monogr. d. Radiol., p. 382, Taf. xv. fig. 5, Taf. xviii. fig. 9.

Spines cylindrical, nearly of equal breadth throughout their whole length. Apex either simple, conical, or bifid. Base with a large leaf-cross, four to six times as broad as the spine itself. Central capsule transparent, yellow. The Atlantic specimens have much longer spines than those figured from the Mediterranean, but are otherwise not different. Therefore I have changed the inconvenient name brevispinum into catervatum.

Dimensions.--Length of the spines 0.1 to 0.3, breadth 0.005 to 0.008; basal leaf-cross 0.02 to 0.032.

Habitat.--Mediterranean (Messina); North Atlantic, Station 354, Gulf Stream (Færöe Channel) in great abundance, John Murray, surface.

Subgenus 3. Astrolithium, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 810.

Definition.--Spines in the basal part grown perfectly together, so that the whole skeleton forms a single piece of acanthin; a star with twenty equal rays.

11. Acanthometron bulbiferum, n. sp. (Pl. 130, fig. 1).

Astrolithium bulbiferum, Haeckel, 1881, Prodromus, p. 466.

Spines needle-shaped, cylindrical, very thin and long, with simple apex; suddenly thickened and forming a broad regular cone at the central base; all twenty conical bulbs have their broad bases grown together and forming a central icosahedron of acanthin; from its twenty faces arise the circular bases of the cones in regular disposition.

Dimensions.--Length of the spines 0.2 to 0.5, breadth 0.001 to 0.003; height of the basal cones 0.06, basal breadth of them 0.02.

Habitat.--Central Pacific, Stations 265 to 274, surface.

12. Acanthometron bifidum, Haeckel.

Astrolithium bifidum, Haeckel, 1862, Monogr. d. Radiol., p. 400, Taf. xx. fig. 5.

Spines needle-shaped, cylindrical, of equal breadth in their whole length. Distal apex bifid, with two parallel straight teeth. Central bases of all twenty spines grown perfectly together and forming a central sphere of acanthin. Central capsule brown opaque.

Dimensions.--Length of the spines 0.2, breadth 0.003.

Habitat.--Mediterranean (Messina), Haeckel, surface.

{746}Genus 324. Zygacantha,[364] J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 51.

Definition.--#Astrolonchida# with simple, compressed, and two-edged radial spines, without apophyses; their transverse section is elliptical or rhomboidal.

The genus Zygacantha comprised in the original definition of J. Müller only a single species, Zygacantha furcata, distinguished from the other #Acanthometra# by forked spines with two long parallel teeth. It seems now advisable to unite in this genus all those Astrolonchida in which the simple spines are two-edged, compressed, or leaf-shaped. The term Zygacantha may be conceived as the general expression of the important fact, that in all Icosacantha the twenty spines are opposite in pairs.

Subgenus 1. Zygacantharium, Haeckel.

Definition.--Spines at the central base without leaf-cross and without hollow pyramidal compartments, united by the opposed triangular faces of their pyramidal bases, resting one upon another.

1. Zygacantha lanceolata, Haeckel.

Acanthometra lanceolata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 48, Taf. xi. fig. 12.

Acanthometra lanceolata, Haeckel, 1862, Monogr. d. Radiol., p. 380.

Spines lanceolate, from the broader middle part equally thinned towards the two ends. Apex simple. Base pyramidal, without leaf-cross. Each flat lamellar spine exhibits an elevated middle rib (like a lanceolate leaf), and is therefore compressed quadrangular.

Dimensions.--Length of the spines 0.1 to 0.15, greatest breadth (in the width) 0.03 to 0.04.

Habitat.--Mediterranean (Saint Tropez, French shore), J. Müller; North Atlantic (Canary Islands), Haeckel, surface.

2. Zygacantha costata, n. sp.

Spines compressed, two-edged, linear, of nearly equal breadth in their whole length. Apex truncate. Base pyramidal, without leaf-cross. Each flat lamellar spine exhibits an elevated middle rib, which in the distal half is cleft into two divergent rods ending in the corners of the truncated apex. (Similar to Zygacantha dicopa, but with broader free spines, which are not grown together in the centre.)

Dimensions.--Length of the spines 0.1 to 0.15, breadth 0.02.

Habitat.--Central Pacific, Stations 265 to 274, surface.

{747}3. Zygacantha compressa, Haeckel.

Acanthometra compressa, Haeckel, 1862, Monogr. d. Radiol., p. 378, Taf. xviii. figs. 4_a_, 4_b_.

Spines in the proximal half compressed, broad lanceolate, four to six times as broad as in the thin cylindrical distal half. Apex simple or short bifid. Base pyramidal, thickened, without leaf-cross. No middle rib. Central capsule opaque, yellowish or reddish-brown.

Dimensions.--Length of the spines 0.3 to 0.5, breadth of the inner half 0.015 to 0.02, of the outer half 0.002 to 0.003.

Habitat.--Mediterranean (Messina); Atlantic (Canary Islands), Station 352, surface.

4. Zygacantha furcata, J. Müller.

Zygacantha furcata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 51, Taf. ix. fig. 6.

Acanthometra furcata, J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 499.

Acanthometra furcata, Haeckel, 1862, Monogr. d. Radiol., p. 380.

Spines compressed, fork-shaped, divided by two thickened knots into three sections of nearly equal length; middle section broader than the proximal, but smaller than the distal section, which is cleft by a deep fissure into two long parallel straight branches. Base pyramidal, without leaf-cross. Central capsule purple, with yellow bodies.

Dimensions.--Length of the spines 0.1 to 0.15, basal breadth 0.003 to 0.005, distal breadth 0.02 to 0.03.

Habitat.--Mediterranean (Cette). J. Müller, surface.

Subgenus 2. Zygacanthidium, Haeckel.

Definition.--Spines at the central base with a cross of four prominent leaves; the meeting edges of the neighbouring lamellæ so rest one upon another that twenty-two hollow pyramidal compartments are formed (compare p. 721).

5. Zygacantha dichotoma, Haeckel.

Zygacantha dichotoma, Haeckel, 1862, Monogr. d. Radiol., p. 381.

Acanthometra dichotoma, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 50, Taf. ix. fig. 5.

Spines compressed, pincer-shaped, cleft nearly throughout their whole length into two thin parallel straight rods or fork branches, which are united only in their middle by a narrow bridge, and at their central base by the pyramidal small central apex; above this pyramid each rod is divided into two broad triangular leaves, forming a large basal leaf-cross. Central capsule purple, with yellow bodies.

Dimensions.--Length of the spines 0.1 to 0.15, breadth 0.01 to 0.02.

Habitat.--Mediterranean (Nice), J. Müller, surface.

{748}6. Zygacantha complanata, n. sp.

Spines compressed, two-edged, linear, of equal breadth throughout their whole length. Apex bifid. Base thickened, with a large leaf-cross. (Similar to Amphilonche complanata, but different in the equal size of all twenty spines, which are somewhat broader.)

Dimensions.--Length of the spines 0.12 to 0.18, breadth 0.002.

Habitat.--North Pacific, Station 244, surface.

7. Zygacantha semicompressa, Haeckel.

Acanthometra hemicompressa, Car, 1884, Zool. Anzeiger, p. 94, with woodcut.

Spines in the proximal half compressed, two-edged, linear, three to four times as broad as in the needle-shaped cylindrical distal half. Apex simple. Base pyramidal, with a small leaf-cross. Central capsule transparent.

Dimensions.--Length of the spines 0.1 to 0.2, breadth in the proximal half 0.02, in the distal half 0.006.

Habitat.--Mediterranean (Genoa), Haeckel; Adriatic Sea (Trieste), Car, surface.

8. Zygacantha foliacea, n. sp.

Spines lanceolate, tapering from the broader middle part towards the two ends, with two dentated or serrated edges and a prominent middle rib. Apex simple. Base with a small leaf-cross. The spines like the leaves of Agave americana.

Dimensions.--Length of the spines 0.15 to 0.2, middle breadth 0.02 to 0.03.

Habitat.--Indian Ocean, near the Island of Socotra, Haeckel.

Subgenus 3. Zygacanthonium, Haeckel.

Definition.--Spines in the centre grown perfectly together and forming a single star-shaped piece of acanthin.

9. Zygacantha dicopa, Haeckel.

Astrolithium dicopum, Haeckel, 1862, Monogr. d. Radiol., p. 400, Taf. xx. figs. 3, 4.

Spines compressed, two-edged, linear, of nearly equal breadth throughout their whole length, with a prominent middle rib, which in the distal third is cleft into two divergent teeth, ending in the two corners of the broad, obliquely truncated apex. All twenty spines with their central bases grown together and forming one single piece of acanthin--a star with twenty rays.

Dimensions.--Length of the spines 0.12 to 0.2, breadth 0.01 to 0.02.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific, many Stations, surface.

{749}Genus 325. Acanthonia,[365] Haeckel, 1881, Prodromus, p. 465.

Definition.--#Astrolonchida# with simple, four-edged, prismatic or pyramidal radial spines, without apophyses; their transverse section is square.

The genus Acanthonia comprises all those Astrolonchida (formerly united with Acanthometron) in which the simple spines either in their whole length or in the greatest part of it are four-edged, with square transverse section. They are sometimes more prismatic (with equal breadth), at other times more pyramidal (with decreasing breadth towards the distal apex). If Acanthometron be the common simple ancestral form of the Acanthonida, then the two-edged Zygacantha, and the four-edged Acanthonia may be regarded as two divergent main lines arising from it; the former leading to the Phractacanthida and Diporaspida, the latter leading to the Stauracanthida and Tessaraspida.

Subgenus 1. Acanthonarium, Haeckel.

Definition.--Spines at the central base, without leaf-cross and without hollow pyramidal compartments, united by the triangular faces of their pyramidal bases, resting one upon another.

1. Acanthonia tetracopa, Haeckel (Pl. 129, figs. 9-11).

Acanthometra tetracopa, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 47, Taf. vii. figs. 3 to 5, Taf. xi. fig. 5.

Acanthometra tetracopa, Haeckel, 1862, Monogr. d. Radiol., p. 379, Taf. xviii. fig. 5.

Spines quadrangular prismatic, with prominent lamellar edges, of equal breadth in their whole length. Base pyramidal, without leaf-cross. Apex truncated, or with four short teeth (sometimes only two teeth). Central capsule opaque, brown or yellow.

Dimensions.--Length of the spines 0.15 to 0.2, breadth 0.01 to 0.012.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, many Stations, surface.

2. Acanthonia prismatica, n. sp.

Spines quadrangular prismatic, without prominent edges, with four plane lateral faces, of equal breadth throughout their whole length. Base pyramidal, without leaf-cross. Apex truncate, with square apical face.

Dimensions.--Length of the spines 0.1 to 0.16, breadth 0.005 to 0.008.

Habitat.--Antarctic Ocean, Station 154, surface.

{750}3. Acanthonia denticulata, n. sp.

Spines quadrangular prismatic, with prominent elegantly denticulated edges, of equal breadth throughout their whole length. Both ends pyramidal, without leaf-cross. (Similar to Amphilonche denticulata, but with the twenty spines all equal, and with spherical central capsule.)

Dimensions.--Length of the spines 0.12 to 0.16, breadth 0.008.

Habitat.--Central Pacific, Stations 266 to 274, surface.

4. Acanthonia mülleri, Haeckel.

Acanthometra mülleri, Haeckel, 1862, Monogr. d. Radiol., p. 379, Taf. xv. fig. 3, Taf. xviii. fig. 6.

Spines quadrangular, nearly prismatic, but tapering gradually from the pyramidal base towards the distal bifid apex, which bears two thin, parallel, or little divergent teeth; four edges elegantly denticulated; base without leaf-cross. Central capsule yellowish or reddish.

Dimensions.--Length of the spines 0.12 to 0.18, basal breadth 0.005.

Habitat.--Mediterranean (Messina); Atlantic, Stations 348 to 352, surface.

5. Acanthonia fragilis, Haeckel.

Acanthometra fragilis, Haeckel, 1862, Monogr. d. Radiol., p. 380, Taf. xv. fig. 4, Taf. xviii. fig. 7.

Spines quadrangular, nearly prismatic, but gradually thickened from the pyramidal base towards the distal truncated end; four edges regularly denticulated; base without leaf-cross. Central capsule opaque.

Dimensions.--Length of the spines 0.5 and more, basal breadth 0.002 to 0.003, distal breadth 0.008 to 0.016 or more.

Habitat.--Mediterranean (Messina); North Atlantic, Station 354, surface.

6. Acanthonia convexa, n. sp.

Spines quadrangular, with four broad lamellar, convex, prominent edges, which from the broader middle part are thinned towards the two emarginated ends; each end with a small quadrangular pyramid, without leaf-cross. All the twenty spines of this species exhibit nearly the same form, which is seen in the caudal or posterior (geotomical) spine of Amphilonche anomala (Monogr. d. Radiol., Taf. xviii. fig. 23, b).

Dimensions.--Length of the spines 0.12 to 0.16, breadth in the middle part 0.02 to 0.025.

Habitat.--North Pacific, Station 244, surface.

7. Acanthonia concava, n. sp.

Spines quadrangular, with four broad lamellar, concave, prominent edges, which from the smaller middle part are broadened towards the two emarginated ends; each end with a small {751}quadrangular pyramid, without leaf-cross. All the twenty spines of this species exhibit nearly the same form, which is seen in the frontal or anterior (hydrotomical) spine of Amphilonche anomala (Monogr. d. Radiol., Taf. xviii. fig. 23, a).

Dimensions.--Length of the spines 0.15, breadth in the middle part 0.012, on both ends 0.025.

Habitat.--South Pacific, Station 288, surface.

8. Acanthonia quadrangula, n. sp.

Spines quadrangular prismatic, with smooth prominent straight edges, but of very different breadth in both halves; the inner or proximal half (inside the central capsule) twice to four times as broad as the outer or distal half (outside the central capsule); both ends suddenly separated by a constriction, in which is inserted the membrane of the capsule. The latter is pellucid, with a number of yellow bodies. Apex of the spines simple, base pyramidal, without leaf-cross.

Dimensions.--Length of the spines 0.2 to 0.4, breadth of the basal half 0.01, of the distal half 0.002 to 0.004.

Habitat.--Atlantic, Canary Islands, Azores, Station 354, surface.

Subgenus 2. Acanthonidium, Haeckel.

Definition.--Spines at the central base with a broad leaf-cross, composed of four prominent triangular lamellæ; the meeting edges of these crossed lamellæ between every three or four neighbouring spines so rest one upon another that twenty-two hollow pyramidal compartments are formed (compare p. 721).

9. Acanthonia echinoides, Haeckel.

Acanthometra echinoides, Claparède et Lachmann, 1858, Études sur les Infusoires et les Rhizopodes, &c., p. 459, pl. xxiii. figs. 1-5.

Acanthometra echinoides, Haeckel, 1862, Monogr. d. Radiol., p. 383.

Spines quadrangular prismatic without prominent edges, with four plane lateral faces, of equal breadth throughout their whole length. Central base three to four times as broad, with large leaf-cross. Apex truncated or bifid (sometimes with four short teeth).

Dimensions.--Length of the spines 0.3 to 0.5, breadth 0.004 to 0.008; leaf-cross 0.02 to 0.03.

Habitat.--North Atlantic, west coast of Norway (Claparède et Lachmann); Færöe Channel (Gulf Stream), John Murray, surface.

10. Acanthonia claparedei, Haeckel.

Acanthometra claparedei, Haeckel, 1862, Monogr. d. Radiol., p. 383, Taf. xviii. fig. 12.

Spines quadrangular prismatic, with four prominent lamellar edges, of equal breadth throughout their whole length. Apex bifid. Central base twice as broad, with large leaf-cross. Central capsule opaque, reddish-brown.

Dimensions.--Length of the spines 0.6, breadth 0.016; leaf-cross 0.032.

Habitat.--Mediterranean (Messina); Atlantic, Station 347, surface.

{752}11. Acanthonia cuspidata, Haeckel.

Acanthometra cuspidata, Haeckel, 1862, Monogr. d. Radiol., p. 383, Taf. xviii. fig. 11.

Spines quadrangular pyramidal, with four prominent lamellar edges, tapering gradually from the broad base towards the simple distal apex. Basal leaf-cross as broad, with a small central pyramid.

Dimensions.--Length of the spines 0.5, basal breadth 0.012; leaf-cross 0.025.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

12. Acanthonia quadrifolia, Haeckel.

Acanthometra quadrifolia, Haeckel, 1862, Monogr. d. Radiol., p. 382, Taf. xviii. fig. 10.

Spines in the basal part quadrangular pyramidal, with four prominent lamellar edges and a large basal leaf-cross; in the distal part three to six times as long, cylindrical, of equal breadth. Apex simple, conical, or bifid. Central capsule yellow or whitish. This common species differs from the nearly allied Acanthometron catervatum mainly by the strong development of the large basal leaves or wings.

Dimensions.--Length of the spines 0.3 to 0.5, breadth in the distal half 0.002, in the basal part 0.02.

Habitat.--Mediterranean; North Atlantic, Stations 252 to 254; Færöe Channel, Gulf Stream, in enormous numbers, John Murray, surface and at various depths.

13. Acanthonia diplopyramis, n. sp.

Spines formed like a quadrangular double pyramid or an irregular octahedron; the basal leaf-cross being extremely developed, with four very large and thin lamellar leaves; the basal halves of the twenty double pyramids are united by the meeting edges of those leaves, while their distal halves are free, with simple apices. Therefore the four triangular leaves of each spine are equally thinned from the middle towards the two ends.

Dimensions.--Length of the spines 0.1 to 0.2, greatest breadth 0.04 to 0.08.

Habitat.--Central Pacific, Stations 266 to 274, surface.

14. Acanthonia multispina, Haeckel.

Acanthometra multispina, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 47, Taf. vii. figs. 6-9.

Acanthometra multispina, Haeckel, 1862, Monogr. d. Radiol., p. 384.

Spines quadrangular, with four lamellar prominent edges, in the proximal half nearly prismatic, in the distal half pyramidal; both halves separated by a prominent short tooth on each edge. Here in the middle part the breadth (including the four teeth) is equal to the basal leaf-cross. Central capsule opaque, brown.

Dimensions.--Length of the spines 0.2 to 0.3, greatest breadth 0.01 to 0.02.

Habitat.--Mediterranean (Messina); Tropical Atlantic, Station 348.

{753}15. Acanthonia serrulata, n. sp.

Spines quadrangular pyramidal, with simple apex; the large basal leaf-cross nearly half as long as the prolonged distal part. The four prominent triangular edges of the latter are very thin and broad lamellæ, finely dentate or serrate.

Dimensions.--Length of the spines 0.2 to 0.3, greatest breadth 0.05 to 0.06.

Habitat.--Central Pacific, Station 272, surface.

Subgenus 3. Acantholithium, Haeckel.

Definition.--Spines in the basal part grown together, so that the whole skeleton is not composed of twenty separated pieces, but represents a single piece of acanthin--a star with twenty equal rays.

16. Acanthonia stellata, n. sp.

Spines quadrangular pyramidal, with simple distal apex, in the basal part grown perfectly together, so that the whole skeleton forms a single piece of acanthin--a starlet with twenty equal rays. The free pyramidal part of each spine is twice to four times as long as the basal part.

Dimensions.--Length of the spines 0.1 to 0.15, greatest breadth (on the surface of the central solid sphere) 0.02 to 0.04.

Habitat.--Central Pacific, Station 271, surface.

Subfamily 2. PHRACTACANTHIDA, Haeckel.

Definition.--#Astrolonchida# with twenty radial spines, each of which bears two opposite apophyses or lateral transverse processes; sometimes two longitudinal rows of opposite apophyses.

Genus 326. Lithophyllium,[366] J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 52.

Definition.--#Astrolonchida# with two simple, not branched, opposite apophyses on each radial spine.

The genus Lithophyllium was founded by J. Müller for a single species (Lithophyllium foliosum), which we also here retain as the type of the genus. It is the first observed Astrolonchid, which bears two opposite lateral apophyses on each spine, and may therefore be regarded as the ancestral form of the subfamily Phractacanthida. The two opposite apophyses are here simple, whilst in the other genera of the subfamily they are branched or multiplied.

{754}1. Lithophyllium cruciatum, Haeckel.

Acanthometra cruciata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 49, Taf xi. fig. 11.

Xiphacantha cruciata, Haeckel, 1862, Monogr. d. Radiol., p. 385, Taf. xviii. fig. 13.

Spines cylindrical, very thin, crossed perpendicularly in the distal third by a thin transverse beam; both lateral rods of the cross have the same length as the distal end. Apex simple. Base pyramidal, without leaf-cross.

Dimensions.--Length of the spines 0.05 to 0.15, breadth 0.001 to 0.002.

Habitat.--Mediterranean, Atlantic, Stations 352 to 354, &c., surface.

2. Lithophyllium gladiatum, n. sp. (Pl. 130, fig. 3).

Spines compressed, sword-shaped, two-edged, crossed perpendicularly in the middle part by a broad, somewhat curved transverse beam; both lateral rods of the cross are triangular compressed, and have the same length as the proximal end. Apex simple. Base pyramidal, without leaf-cross.

Dimensions.--Length of the spines 0.2 to 0.25, breadth 0.01.

Habitat.--North Pacific, Station 241, surface.

3. Lithophyllium condylatum, n. sp.

Spines compressed quadrangular, tapering from the broader middle towards the two ends; from the middle part arise two opposite perpendicular apophyses, which bear on the rounded end a thickened condyle. Apex simple. Base pyramidal, with a small leaf-cross.

Dimensions.--Length of the spines 0.1 to 0.12, breadth in the middle part 0.02.

Habitat.--Central Pacific, Station 266 to 272, surface.

4. Lithophyllium foliosum, J. Müller.

Lithophyllium foliosum, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 52, Taf. xi. figs. 6-10.

Xiphacantha foliosa, Haeckel, 1862, Monogr. d. Radiol., p. 385.

Spines lanceolate, tapering from the broader middle towards the two ends. From the middle part or from the outer third arise two opposite triangular apophyses, which are not perpendicular to the axis of the spine, but form an acute angle with its distal part. Therefore each spine represents a broad leaf with a middle rib and with three lobes or truncated teeth. The distal apex is distinguished by a violet colour. Base pyramidal, without leaf-cross. Central capsule yellow.

Dimensions.--Length of the spines 0.05 to 0.1, breadth 0.02 to 0.03.

Habitat.--Mediterranean, French shore, Saint Tropez, J. Müller.

{755}Genus 327. Phractacantha,[367] Haeckel, 1881, Prodromus, p. 465.

Definition.--#Astrolonchida# with two branched, but not latticed, opposite apophyses on each radial spine.

The genus Phractacantha differs from its ancestral form, the preceding Lithophyllium by the ramification of the apophyses, which are either forked or bear lateral branches. If the prolonged fork-branches of the neighbouring spines meet and form a lattice-shell, this genus passes over into Phractaspis, the common ancestral form of the Diporaspida.

1. Phractacantha bifurca, n. sp.

Spines cylindrical, thin, of equal breadth throughout their whole length. Apex simple. Base pyramidal, without leaf-cross. From the outer third arise two opposite, thin, forked apophyses; ends of the fork branches acute.

Dimensions.--Length of the spines 0.1, breadth 0.006.

Habitat.--Central Pacific, Station 274, surface.

2. Phractacantha bipennis, n. sp.

Spines compressed, two-edged, tapering from the broader middle towards the two ends. Apex simple. Base pyramidal, without leaf-cross. From the middle arise two opposite broad, forked apophyses; ends of the fork-branches broad and obtuse.

Dimensions.--Length of the spines 0.15, breadth in the middle 0.012.

Habitat.--Central Pacific, Station 266, surface.

Genus 328. Doracantha,[368] Haeckel, 1881, Prodromus, p. 465.

Definition.--#Astrolonchida# with two latticed or fenestrated apophyses on each radial spine.

The genus Doracantha arises from the foregoing Phractacantha by union of the fork-branches of the apophyses on each spine. By this concrescence is formed a polygonal or roundish plate with two pores, pierced by the radial spine between them. Doracantha may be regarded as a Dorataspis, in which the twenty small fenestrated plates have not become united.

{756}1. Doracantha dorataspis, n. sp.

Spines compressed, two-edged, tapering from the broader middle towards the two ends. Apex simple. Base pyramidal, without leaf-cross. From the middle part of each spine arise two opposite forked apophyses; the neighbouring fork-branches are recurved and united in the tangential plane; so that each spine bears a plate or shield with two elliptical pores; the margin of the roundish plate bears a variable number of short teeth.

Dimensions.--Length of the spines 0.2, breadth 0.02.

Habitat.--Central Pacific, Station 271, surface.

Genus 329. Astrolonche,[369] Haeckel, 1881, Prodromus, p. 465.

Definition.--#Astrolonchida# with numerous simple apophyses (four to eight or more on each radial spine), which are arranged in two opposite longitudinal rows (rarely in six such rows, opposite in three parallel planes).

The genus Astrolonche differs from the preceding Phractacanthida in the multiplication of the simple apophyses. Commonly these are opposite in pairs in two longitudinal rows (on the two edges of the compressed spine, at least two on each side). But sometimes (in the subgenus Astrolonchidium) there are six instead of two longitudinal rows of teeth, and these are placed in three parallel planes.

Subgenus 1. Astroloncharium, Haeckel.

Definition.--Each spine with two longitudinal rows of apophyses, opposite in one meridian plane.

1. Astrolonche bicruciata, n. sp.

Spines compressed, two-edged, almost of equal breadth throughout their whole length, with simple apex and small leaf-cross at the base. From the two edges of the middle part of each spine arise two pairs of opposite apophyses, which are compressed and a little curved (convex on the distal, concave on the proximal margin). All four apophyses are of the same size and form; the radial distance of each pair much smaller than their common distance from the centre.

Dimensions.--Length of the spines 0.25, breadth 0.02.

Habitat.--Central Pacific, Station 270, surface.

2. Astrolonche mucronata, Haeckel.

Acanthometra mucronata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 49, Taf. x. fig. 9.

Aspidomma mucronatum, Haeckel, 1862, Monogr. d. Radiol., p. 424.

Spines conical, little compressed, with simple apex and small leaf-cross at the base. From the basal half of each spine arise two pairs of opposite apophyses, which exhibit a very different form. {757}The upper or distal apophyses (nearly in the middle of the spine) are flat, leaf-shaped, broadened in the periphery, often lobed, and sometimes branched or even fenestrated. (Transition to Phractaspis and Dorataspis, or to Phractopelta?) The lower or proximal apophyses are thick, simple, all slightly curved; they are equidistant from the former and from the centre.

Dimensions.--Length of the spines 0.2 to 0.3, greatest breadth 0.01.

Habitat.--Mediterranean (Cette on the French shore), surface, J. Müller.

3. Astrolonche pectinata, Haeckel.

Acanthometra pectinata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 48, Taf. x. figs. 1, 2.

Xiphacantha pectinata, Haeckel, 1862, Monogr. d. Radiol., p. 386.

Spines compressed quadrangular, with short, simple or bifid apex, pyramidal on the base, without leaf-cross. From the two broader edges of the proximal half arise two longitudinal rows of opposite apophyses; three to four slender teeth in each row.

Dimensions.--Length of the spines 0.2, breadth 0.08.

Habitat.--Mediterranean, Cette (French shore), surface, J. Müller.

4. Astrolonche pinnata, n. sp.

Spines in the distal half compressed, linear, two-edged, with bifid apex; in the proximal half three times as broad lanceolate, at the base pyramidal, without leaf-cross. From the two broader edges of the proximal half arise two longitudinal rows of opposite apophyses; four to six broad triangular teeth in each row.

Dimensions.--Length of the spines 0.3 to 0.4, breadth in the outer half 0.012, in the inner half 0.03 to 0.04.

Habitat.--South Atlantic, Station 332, surface.

Subgenus 2. Astrolonchidium, Haeckel.

Definition.--Each spine with three parallel double rows of opposite apophyses.

5. Astrolonche serrata, Haeckel.

Xiphacantha serrata, Haeckel, 1862, Monogr. d. Radiol., p. 386, Taf. xvii. fig. 3, Taf. xviii. figs. 14_a_, 14_b_.

Xiphacantha serrata, R. Hertwig, 1879, Organismus d. Radiol., p. 11, Taf. ii. fig. 4.

Acanthometra serrata, Haeckel, 1860, Monogr. d. Radiol., p. 807.

Spines in the distal half thin, nearly cylindrical or a little compressed, thinned towards the short simple or bifid apex; in the proximal half three to six times as broad, four-winged, with six longitudinal rows of opposite apophyses. From the edges of the two broader (lateral) wings arise three {758}to four pairs of strong conical teeth; from the edges of the two smaller (sagittal) wings arise also three to four pairs of teeth, but very short and broad, triangular; each of these teeth bears on both its (lateral) sides two opposite slender conical teeth, which are parallel to the large conical teeth of the lateral wings. Therefore all teeth (eighteen to twenty-four) are placed opposite in pairs in three parallel planes. Base of the spines pyramidal, with a small leaf-cross. The central capsule of this large and very remarkable species commonly entirely includes the apophyses of the spines, and is opaque, whitish.

Dimensions.--Length of the spines 0.2 to 0.3, breadth of the distal half 0.002 to 0.004, of the proximal half 0.01 to 0.02.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

Subfamily 3. STAURACANTHIDA, Haeckel.

Definition.--#Astrolonchida# with a cross of four free apophyses (or four crossed longitudinal rows of apophyses) on each radial spine.

Genus 330. Xiphacantha,[370] Haeckel, 1862, Monogr. d. Radiol., p. 384.

Definition.--#Astrolonchida# with four simple apophyses on each radial spine, opposite in pairs in the form of a cross.

The genus Xiphacantha was founded by me in 1862 for all those Acanthometrida which bear simple or branched apophyses on their twenty equal spines. I restrict here the genus to those Astrolonchida which bear on each spine a cross of four simple, not branched, apophyses. These are either conical teeth or broad wings, sometimes extremely thin leaves. Xiphacantha may be regarded as the ancestral form not only of the subfamily Stauracanthida, but also of the Tessaraspida, derived from the latter.

Subgenus 1. Xiphacanthonia, Haeckel.

Definition.--Apophyses of the radial spines small, formed like a tooth or a hook, not wing-shaped. Edges of the spines commonly narrow, little prominent.

1. Xiphacantha quadridentata, Haeckel.

Xiphacantha quadridentata, Haeckel, 1862, Monogr. d. Radiol., p. 387, Taf. xviii. figs. 15_a_, 15_b_.

Acanthometra quadridentata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 48, Taf. x. fig. 3.

Spines slender, four-sided prismatic, gradually thinner towards the simple pyramidal apex. Base with large wing-cross. Four apophyses about in the middle of each spine, conical, straight, smooth, about as long as the basal breadth of the spine. Central capsule opaque, reddish-brown.

{759}Dimensions.--Length of the spines 0.2 to 0.3, breadth in the middle part 0.012, on the base 0.02; length of the apophyses 0.02 to 0.03.

Habitat.--Mediterranean, Atlantic, Stations 348, 354, surface.

2. Xiphacantha crucifera, n. sp.

Spines slender, four-sided prismatic, thin, of nearly equal breadth throughout the whole length. Base with small wing-cross. Four apophyses much nearer the proximal than the distal end, thin, straight smooth, three to six times as long as the basal breadth of the spine. Central capsule pellucid, with yellow bodies.

Dimensions.--Length of the spines 0.4 to 0.5, breadth 0.002 to 0.004; length of the apophyses 0.01 to 0.02.

Habitat.--Central Pacific, Station 266, surface.

3. Xiphacantha spinulosa, Haeckel.

Xiphacantha spinulosa, Haeckel, 1862, Monogr. d. Radiol., p. 388, Taf. xvii. fig. 4.

Acanthometra spinulosa, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 807.

Spines stout, four-sided prismatic, of nearly equal breadth throughout the whole length, on the distal apex truncated, two-edged. Base with large wing-cross. Four apophyses about in the middle of each spine, conical, straight, spinulated, twice to four times as long as the basal breadth of the spine. Central capsule opaque, yellow.

Dimensions.--Length of the spines 0.27, breadth 0.014; length of the apophyses 0.05.

Habitat.--Mediterranean (Messina), surface.

4. Xiphacantha emarginata, n. sp.

Spines stout, four-sided, in the proximal half prismatic, in the distal half pyramidal, with emarginated apex. Base with very large wing-cross. Four apophyses about in the middle of each spine, compressed, straight, two-edged, with emarginated ends, about twice as long as the basal breadth of the spine. Central capsule small, pellucid.

Dimensions.--Length of the spines 0.2 to 0.3, breadth 0.02 to 0.03; length of the apophyses 0.04 to 0.06.

Habitat.--South Pacific, Station 291, surface.

5. Xiphacantha falcata, n. sp.

Spines slender, four-sided prismatic, gradually thickened from both ends towards the middle part, with simple apex. Base with very small wing-cross. Four apophyses about in the middle part of each spine, falcated, compressed, recurved, twice to three times as long as the greatest breadth of the spine.

{760}Dimensions.--Length of the spines 0.3 to 0.4, greatest breadth 0.015; length of the apophyses 0.03 to 0.05.

Habitat.--Central Pacific, Station 270, surface.

6. Xiphacantha ancorata, n. sp.

Spines slender, four-sided prismatic, gradually thickened from the narrow base towards the short, simple, pyramidal apex. Base with large wing-cross. Four apophyses on the distal end, immediately below the pyramidal apex, falcated, strongly recurved, like an anchor with four strong teeth.

Dimensions.--Length of the spines 0.4 to 0.5, basal breadth 0.005, distal breadth 0.015; length of the apophyses 0.04.

Habitat.--Indian Ocean, Madagascar, Rabbe.

Subgenus 2. Xiphacanthidium, Haeckel.

Definition.--Apophyses of the radial spines broad, compressed, wing-shaped, formed like a large thin plate. Edges of the spines commonly broad, strongly prominent.

7. Xiphacantha stauroptera, n. sp.

Spines four-winged, from the middle part little thinner towards both ends. Apex simple pyramidal. Base with small wing-cross. Four apophyses wing-shaped, isosceles triangular or truncated quadrangular; their base is about half as broad as their length, and occupies in the basal half of each spine about one-sixth to one-eighth of its length.

Dimensions.--Length of the spines 0.1 to 0.15; greatest breadth (diagonal of the cross of the apophyses) 0.006 to 0.009.

Habitat.--South Atlantic, Station 332, surface.

8. Xiphacantha trigonoptera, n. sp.

Spines four-winged, tapering rapidly from the broad middle part towards both ends. Apex simple pyramidal. Base with a small wing-cross. Four apophyses equilateral triangular; their base occupies the middle of each spine, extending to about one-fifth of its length.

Dimensions.--Length of the spines 0.15 to 0.2, greatest breadth (diagonal of the cross of the apophyses) 0.06 to 0.08.

Habitat.--Central Pacific, Station 272, surface.

9. Xiphacantha macroptera, n. sp.

Spines four-winged, from the broad middle part gradually thinner towards both ends. Apex simple pyramidal. Base with small wing-cross. Four apophyses wing-shaped, very long and broad, {761}triangular; their base occupies about the middle third of each spine; the proximal side of each wing is the shortest, truncated or concave.

Dimensions.--Length of the spines 0.4 to 0.5, greatest breadth (diagonal of the middle leaf-cross) 0.08 to 0.12.

Habitat.--North Pacific, Stations 253 to 256, surface.

10. Xiphacantha platyptera, n. sp.

Spines four-winged, nearly prismatic in the basal and distal parts. Apex truncated. Base with small wing-cross. Four apophyses wing-shaped, very broad and thin, extremely delicate, of irregular quadrangular or nearly rhomboidal form; their base occupies the middle half of the length of the spines (second and third quarter). Very variable in form. Often the edges of the wing-apophyses of the neighbouring spines seem to meet.

Dimensions.--Length of the spines 0.2 to 0.3, greatest breadth (diagonal of the leaf-cross) 0.06 to 0.08.

Habitat.--Pacific, widely distributed, Stations 239, 253, 272, 288, &c., surface.

11. Xiphacantha ciliata, n. sp. (Pl. 129, figs. 4, 5).

Spines four-winged, prismatic in the basal and the distal third. Apex pyramidal, short. Base with large leaf-cross. Four apophyses wing-shaped, nearly semicircular, with dentated edges and rough spinulate or porous faces; their base occupies the middle third of the length of each spine.

Dimensions.--Length of the spines 0.2 to 0.3, greatest breadth (diagonal of the apophysial cross) 0.08 to 0.12.

Habitat.--Tropical Atlantic, Stations 342 to 352, surface.

12. Xiphacantha alata, Haeckel.

Xiphacantha alata, Haeckel, 1862, Monogr. d. Radiol., p. 388.

Acanthometra alata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 48, Taf. ix. figs. 1-3.

Spines four-winged, prismatic in the basal quarter, more slender in the distal half. Apex simple pyramidal. Base with small wing-cross. Four apophyses wing-shaped, nearly semicircular, with denticulated edges (and often also with spinulate faces); their base occupies the second quarter of the length of each spine.

Dimensions.--Length of the spines 0.3 to 0.4, greatest breadth (diagonal of the apophysial cross) 0.05 to 0.06.

Habitat.--Mediterranean (Nice), Müller, (Portofino), Haeckel.

Genus 331. Stauracantha,[371] Haeckel, 1881, Prodromus, p. 465.

Definition.--#Astrolonchida# with four branched (but not latticed) apophyses on each radial spine, opposite in pairs in the form of a cross.

{762}The genus Stauracantha differs from its ancestral form, Xiphacantha, in the ramification of the four crossed apophyses on each spine. These bear either lateral branches, which are parallel to the cross axes of the radial spine itself (subgenus Stauracanthonium), or they are forked, with divergent branches not parallel to those cross axes (subgenus Stauracanthidium). Both subgenera may perhaps be better separated as genera. They form the transition to the Stauraspida.

Subgenus 1. Stauracanthonium, Haeckel.

Definition.--Apophyses of the radial spines not forked, but crossed by perpendicular branches, which are placed in tangential planes and parallel to the cross axes of the quadrangular spine itself.

1. Stauracantha orthostaura, n. sp. (Pl. 130, fig. 5).

Spines four-sided prismatic, with simple apex and small leaf-cross at the base; with four thin slender conical apophyses in the proximal third. Each apophysis represents a regular rectangular cross, being intersected in its middle by one perpendicular rod of its own length.

Dimensions.--Length of the spines 0.3, breadth 0.02; distance of the apophyses from the apex 0.15 to 0.2.

Habitat.--South Pacific, Station 169, surface.

2. Stauracantha tetrastaura, n. sp.

Spine four-winged prismatic, with four broad prominent edges, pyramidal apex, and large basal leaf-cross, with four broad compressed apophyses about in the middle. Each apophysis represents a vertical lamella (placed in a meridian) with convex distal and concave proximal edge, and is crossed in its apical part by one perpendicular short rod.

Dimensions.--Length of the spines 0.5, breadth 0.03; distance of the apophyses from the centre 0.2.

Habitat.--Central Pacific, Station 272, surface.

3. Stauracantha diplostaura, n. sp.

Spines four-sided prismatic, with truncated apex and broad basal leaf-cross; in the proximal half with four slender conical apophyses. Each apophysis is crossed in its apical half at right angles by two short parallel transverse rods.

Dimensions.--Length of the spines 0.32, breadth 0.012; distance of the apophyses from the centre 0.11.

Habitat.--South Pacific, Station 291, surface.

{763}4. Stauracantha scalaris, n. sp.

Spines four-winged prismatic, with four broad prominent edges, truncated apex, and small basal leaf-cross; in the proximal third with four compressed lamellar apophyses. Each apophysis is pinnate with opposite pinnulæ, or crossed at right angles by three to six parallel transverse rods.

Dimensions.--Length of the spines 0.24, breadth 0.016; central distance of the apophyses 0.12.

Habitat.--Indian Ocean (Madagascar), Rabbe, surface.

5. Stauracantha johannis, n. sp. (Pl. 132, fig. 11).

Spines four-sided pyramidal, with simple apex and broad basal leaf-cross, with four large conical apophyses about in their middle. Each apophysis bears two irregular rows of alternating perpendicular lateral branches, the length of which decreases from the base towards the apex of the apophysis.

Dimensions.--Length of the spines 0.2, middle breadth 0.02; central distance of the apophyses 0.1.

Habitat.--South-east Pacific (off Juan Fernandez), Station 300, surface.

6. Stauracantha murrayana, Haeckel.

Xiphacantha species, Wyville Thomson, 1877, The Atlantic, vol. i. p. 235, fig. 53.

Xiphacantha murrayana, Haeckel, 1878, Protistenreich, p. 45, fig. 33.

Spines quadrangular prismatic, with pyramidal apex and small basal leaf-cross, with four regular conical apophyses in the proximal part. Each apophysis is crossed at right angles by two parallel transverse rods; the smaller apical rod is simple; the larger basal rod is crossed again on each side by a secondary perpendicular branch, which therefore is parallel to the apophysis itself.

Dimensions.--Length of the spines 0.3, breadth 0.01, distance of the apophyses 0.08.

Habitat.--South Atlantic, Station 332, surface.

7. Stauracantha pinnulata, n. sp.

Spines four-winged pyramidal, with prominent edges, simple apex and large basal leaf-cross, in the middle with doubly pinnate triangular apophyses. Each apophysis is crossed at right angles by three to four transverse parallel rods, which bear again perpendicular secondary branches; the outline of the doubly pinnate apophysis is an isosceles triangle.

Dimensions.--Length of the spines 0.3, middle breadth 0.02; distance of the apophyses 0.12.

Habitat.--North Pacific, Station 244, surface.

{764}Subgenus 2. Stauracanthidium, Haeckel.

Definition.--Apophyses of the radial spines forked, each with two divergent terminal branches, which are not parallel to the cross axes of the quadrangular spine.

8. Stauracantha stauraspis, Haeckel.

Dorataspis polyancistra, juvenis, Haeckel, 1862, Monogr. d. Radiol., p. 418, Taf. xxi. fig. 7.

Spines slender, quadrangular prismatic, with simple apex and pyramidal base (without basal leaf-cross); with four slender apophyses, which are simply forked in the outer third. Each apophysis with two recurved fork branches.

Dimensions.--Length of the spines 0.12, breadth 0.004; distance of the apophyses 0.06.

Habitat.--Mediterranean (Messina), surface.

9. Stauracantha bifurca, n. sp.

Spines stout, four-winged prismatic, with pyramidal apex and pyramidal base (without leaf-cross); in their middle with four compressed, little curved apophyses (convex on the outer, concave on the inner edge), which are simply forked at the end. Each apophysis with two short straight fork branches.

Dimensions.--Length of the spines 0.2, breadth 0.006; distance of the apophyses 0.08.

Habitat.--Central Pacific, Station 266, surface.

10. Stauracantha quadrifurca, n. sp. (Pl. 130, fig. 4).

Spines slender, four-sided prismatic, with simple apex and pyramidal base (without leaf-cross); with four slender apophyses, which are doubly forked about in their middle. Each apophysis with four short and thin terminal branches.

Dimensions.--Length of the spines 0.2, breadth 0.002; distance of the apophyses from the centre 0.08.

Habitat.--South Atlantic, Stations 325 to 330, surface.

Genus 332. Phatnacantha,[372] Haeckel, 1881, Prodromus, p. 465.

Definition.--#Astrolonchida# with four apophyses on each radial spine, opposite in pairs in cross form, and forming a lattice-plate by communicating branches.

The genus Phatnacantha has been derived from the preceding Stauracantha by concrescence of the branches of the apophyses. Therefore each spine bears a lattice-plate or a fenestrated shield. If the growing plates of the neighbouring spines {765}meet together, then the characteristic lattice-shell of the Tessaraspida is perfect. Either each plate bears four crossed pores (like Tessaraspis), or a larger number of pores (four aspinal and four to eight or more coronal) like Icosaspis.

1. Phatnacantha tessaraspis, n. sp.

Spines quadrangular prismatic, with simple pyramidal apex and small basal leaf-cross. Each spine bears in the basal half a square plate, which is perforated by four square pores; margin of the plate with twelve short straight teeth.

Dimensions.--Length of the spines 0.12, breadth 0.005.

Habitat.--Central Pacific, Station 265, surface.

2. Phatnacantha icosaspis, n. sp. (Pl. 130, fig. 6).

Spines quadrangular with prominent edges; prismatic in the basal half, with a broad basal leaf-cross, pyramidal in the distal half, with a simple or truncate apex. Each spine bears in the middle part a square plate, which is perforated by eight to sixteen or more square pores (four aspinal and four to eight or more coronal); margin of the plate with twenty-four to forty-eight or more short straight irregular compressed teeth.

Dimensions.--Length of the spines 0.18, breadth 0.008.

Habitat.--Central Pacific, Station 273, surface.

Genus 333. Pristacantha,[373] n. gen.

Definition.--#Astrolonchida# with numerous simple apophyses (eight to sixteen or more on each radial spine) which are arranged in four longitudinal rows opposite in pairs in the form of a cross.

The genus Pristacantha differs from all other Stauracanthida in the multiplication of the crossed apophyses (at least eight on each spine), and exhibits therefore to them the same relation as Astrolonche exhibits to the other Phractacanthida. The remarkable Astrolonchidium serratum appears intermediate between both groups.

1. Pristacantha octodon, n. sp. (Pl. 130, fig. 9).

Spines four-sided prismatic, a little broader in the middle part than at either end, with thin prominent edges. Apex truncate or pyramidal. Base pyramidal, with a small leaf-cross. From the four edges arise in the basal half (between first and second third of the length) eight slender, conical, or triangular apophyses (two on each edge).

Dimensions.--Length of the spines 0.4 to 0.6, breadth 0.02 to 0.04.

Habitat.--Central Pacific, Station 271, surface.

{766}2. Pristacantha dodecodon, n. sp. (Pl. 130, fig. 8).

Spines four-winged, of lanceolate outline, tapering from the broader middle towards the two ends. Apex pyramidal. Base with a large leaf-cross. From the four wings arise in the basal part (between first and second third of the length) twelve triangular apophyses (three from each wing).

Dimensions.--Length of the spines 0.3, breadth in the middle 0.03.

Habitat.--North Pacific, Station 244, surface.

3. Pristacantha polyodon, n. sp. (Pl. 130, fig. 7).

Spines in the distal half four-sided prismatic, thin, with pyramidal apex; in the basal half much broader, four-winged, with a large leaf-cross on the base. From the four wings of the basal half arises a variable number of slender teeth or triangular apophyses, commonly sixteen to twenty-four, often irregular (four to six from each wing).

Dimensions.--Length of the spines 0.3 to 0.4, breadth in the distal part 0.007 to 0.01, in the basal part 0.02 to 0.03.

Habitat.--South Pacific (off New Zealand), Station 169, surface.

Family XXXVII. #QUADRILONCHIDA#, Haeckel (Pl. 131).

Acanthostaurida, Haeckel, 1881, Prodromus, p. 466.

Definition.--ACANTHARIA with twenty radial spines of very unequal size, disposed according to the law of the Icosacantha; four equatorial spines much larger than the sixteen others. No lattice-shell.

The family #Quadrilonchida# differs from the foregoing ancestral family, the Astrolonchida, in the unequal development of the twenty radial spines. The four equatorial spines are constantly much larger, and often also of another form and shape, than the sixteen other spines; often also among these the eight tropical spines are larger and of another form than the eight polar spines. Therefore the five parallel girdles or zones of every four spines, which in the Astrolonchida are equal, are here distinctly unequal. The whole body is flattened and compressed in the direction of the spineless axis, so that the equatorial plane is larger than any other plane, laid through the centre. In consequence of this flattening the central capsule is also commonly compressed and flattened, lenticular or discoidal, rarely spherical. In the Astrolonchida the "promorph" or the "geometrical fundamental form" is constantly a square double pyramid, the axes of which are of equal length. In the Quadrilonchida it becomes a square double pyramid, the two equatorial axes of which (or the diagonals of the square) are constantly longer than all other axes.

In the simpler forms of Quadrilonchida are found only two different kinds of spines, the four larger equatorial spines being of the same size and form, and the sixteen smaller {767}spines also not differing from one another (Acanthostaurus, &c.). But in the majority of this family there are three different kinds: four larger equatorial spines, eight tropical spines of middle size, and eight smaller polar spines (Belonostaurus, &c.); the latter become sometimes rudimentary, so that only twelve spines are developed (four larger equatorial and eight smaller tropical spines). In this case the development of the flat discoidal body is much stronger in the equatorial plane than in all other planes. These discoidal or lenticular Quadrilonchida exhibit a relation to the spherical Astrolonchida similar to that which the #Discoidea# exhibit to the #Sphæroidea# among the #Sphærellaria#.

A further morphological differentation takes place in the remarkable genera Lonchostaurus and Zygostaurus. In the former (Pl. 131, figs. 4-6) the four larger equatorial spines becomes differentiated in pairs, so that the opposite equal spines of one pair, _c_1, _c_3 (in the longitudinal or hydrotomical axis), are larger, and often also of another form, than the opposite equal spines of the other pair, _c_2, _c_4 (in the transverse or geotomical axis). The most peculiar form is the rather common Zygostaurus (Pl. 131, figs. 7, 8). Here the two opposite spines of one equatorial axis (of the longitudinal axis) become very different, so that the anterior or frontal spine (_c_1) is very unequal to the posterior or caudal spine (_c_3), whereas the two opposite spines, of the other equatorial axis (of the transverse axis) remain equal (_c_2, _c_4). Therefore the fundamental forms become here "amphithect," as in the Ctenophora.

The numerous Quadrilonchida may be disposed in two different subfamilies: in the Acanthostaurida all twenty radial spines are simple, without apophyses; in the Lithopterida all twenty spines (or only one part of them) bear two opposite apophyses (or lateral transverse processes). The former correspond to the Zygacanthida, the latter to the Phractacanthida among the Astrolonchida. The two opposite apophyses are simple in Quadrilonche (Pl. 133, fig. 1). In Xiphoptera they are provided on their distal side with lateral branches which are parallel to the spine itself. In Lithoptera the spines bear two to four parallel pairs of transverse apophyses, and these are crossed by perpendicular branches, parallel to the spine itself, so that there arise fenestrated wings or latticed plates, comparable to the sails of a wind-mill. The lattice-work of these plates lies in the same meridian plane with the radial spine itself, and is therefore not comparable to the fenestrated apophyses of Doracantha, of Phatnacantha, and of the Dorataspida; in these the lattice-plates lie in tangential planes, perpendicular to the radial spine.

The apophyses of the Lithopterida may be developed either on all twenty spines equally, or only on twelve spines (four equatorial and eight tropical, whilst the eight polar spines are simple, Pl. 131, fig. 10), or only on the four equatorial spines (whilst the sixteen others are simple, Pl. 131, fig. 9).

The Central Capsule of the Quadrilonchida is rarely spherical, commonly more or {768}less compressed from both poles of the spineless axis, lenticular or discoidal, sometimes square. It is enveloped by a voluminous calymma constantly bearing coronals of "Myophrisca" (compare p. 724).

Synopsis of the Genera of Quadrilonchida.

------------------------------------------------------------------------- I. Subfamily Acanthostaurida. All twenty spines simple, without lateral apophyses (sometimes forked, but neither branched nor latticed). ------------------------------------------------------------------------- { Eight tropical and { eight polar spines { nearly equal, 334. Acanthostaurus. Four equatorial spines of { equal size and form. { Eight tropical and { eight polar spines { very different, 335. Belonostaurus.

{ Two principal spines Four equatorial spines of { of equal size and very different size or { form, 336. Lonchostaurus. form (the two lateral { constantly equal). { Two principal spines { (frontal and caudal) { very different, 337. Zyostaurus. ------------------------------------------------------------------------- II. Subfamily Lithopterida. Either all twenty spines or a part of them provided with two opposite lateral branches or apophyses. ------------------------------------------------------------------------- Apophyses simple, neither branched nor latticed, 338. Quadrilonche.

Apophyses branched or pinnate, but not latticed, 339. Xiphoptera.

Apophyses latticed, with fenestrated network, 340. Lithoptera.

Subfamily 1. ACASTHOSTAURIDA, Haeckel, 1881, Prodromus, p. 466.

Definition.--#Quadrilonchida# with simple radial spines, without apophyses.

Genus 334. Acanthostaurus,[374] Haeckel, 1862, Monogr. d. Radiol., p. 395.

Definition.--#Quadrilonchida# with four equatorial spines of equal size and form, which are much larger than the sixteen other spines. Eight tropical and eight polar spines nearly equal. No apophyses.

The genus Acanthostaurus is the most simple and primitive form of the Quadrilonchida, and the common ancestral genus of this family; it is at the same time its most common and widely distributed form. Some species appear in astonishing numbers in different seas. It has been derived from Acanthometron by stronger development of the four equatorial spines, which are all of equal size and much larger than the sixteen others.

{769}Subgenus 1. Acostaurus, Haeckel.

Definition.--All twenty spines separated, in the centre united only by the triangular faces or the meeting leaf-shaped edges of their pyramidal bases.

1. Acanthostaurus aequatorialis, n. sp.

Spines cylindrical, of nearly equal breadth throughout their whole length. Apex simple conical. Base with a large leaf-cross. Four equatorial spines of the same form as the sixteen others, but much longer and about three times as broad.

Dimensions.--Length of the four major spines 0.2 to 0.25, breadth 0.008; length of the sixteen minor spines 0.01 to 0.15, breadth 0.003.

Habitat.--Equatorial Pacific, Station 271, surface.

2. Acanthostaurus bipennis, n. sp.

Spines linear, sword-shaped, strongly compressed, two edged; of nearly equal breadth in their whole length. Apex bifid. Base with a small leaf-cross. Four equatorial spines of the same form as the sixteen others, but twice as long and as broad.

Dimensions.--Length of the four major spines 0.4 to 0.5, of the sixteen minor 0.2 to 0.3; breadth of the former 0.02, of the latter 0.01.

Habitat.--North Pacific, Station 244, surface.

3. Acanthostaurus conacanthus, n. sp.

Spines conical, short, gradually tapering from the thick base towards the simple apex. Base with large leaf-cross. Four equatorial spines more cylindrical, twice to three times as long and as broad as the sixteen others.

Dimensions.--Length of the four major spines 0.15 to 0.2, of the sixteen minor 0.05 to 0.08; basal breadth of the former 0.03, of the latter 0.012.

Habitat.--South Atlantic, Station 332, surface.

4. Acanthostaurus purpurascens, Haeckel.

Acanthostaurus purpurascens, Haeckel, 1862, Monogr. d. Radiol., p. 395, Taf. xix. figs. 1, 2.

Acanthostaurus purpurascens, R. Hertwig, 1879, Organism. d. Radiol., Taf. i. figs. 8, 9, Taf. iii. figs. 13, 15.

Acanthometra purpurascens, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 809.

Spines nearly cylindrical, with four blunt (often scarcely visible) edges, tapering slightly from the central to the distal end. Apex bifid, with two short parallel teeth. Base with a broad leaf-cross. {770}Four equatorial spines one and a half times to twice as long and broad as the sixteen others. Central capsule cruciate, with four arms (enveloping the basal part of the four large spines); filled up with yellow bodies and purple granules. Calymma large, with a network of purple granules. The four main spines are constantly much larger than the sixteen others, but in variable proportion. The eight polar spines are sometimes rudimentary.

Dimensions.--Length of the four major spines 0.3 to 0.4, of the sixteen minor 0.15 to 0.3; breadth of the former 0.012, of the later 0.008 or less.

Habitat.--Mediterranean (Messina); Atlantic, Stations 348 to 354, surface.

5. Acanthostaurus pallidus, Haeckel.

Acanthostaurus pallidus, Haeckel, 1862, Monogr. d. Radiol., p. 396.

Acanthometra pallida, Claparède et Lachmann, 1858, Études sur les Infusoires, &c., p. 461, Taf. xxiv. fig. 6.

Spines four-sided prismatic, with four blunt edges, of nearly equal breadth throughout their whole length. Apex bifid. Base with a small leaf-cross. Four equatorial spines much larger than the sixteen others. Central capsule spherical, transparent, containing some yellow bodies.

Dimensions.--Length of the four main spines 0.12 to 0.2, of the sixteen others 0.04 to 0.08; breadth of the former 0.01, of the latter 0.004.

Habitat.--North Atlantic, west coast of Norway, Claparède; Færöe Channel, John Murray.

6. Acanthostaurus forceps, Haeckel.

Acanthostaurus forceps, Haeckel, 1862, Monogr. d. Radiol., p. 396, Taf. xix. figs. 3, 4.

Acanthometra forceps, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 809.

Spines pincer-shaped, linear, compressed, cleft nearly throughout their whole length into two parallel thin, straight branches, which are united only at the pyramidal base and by means of a small bridge in the middle part. Four main spines twice as long and as broad as the sixteen others. Central capsule square, filled up with red pigment, and containing yellow bodies. The diagonals of the square are the two equatorial axes.

Dimensions.--Length of the four main spines 0.1, of the sixteen others 0.05; breadth of the former 0.01, of the latter 0.005.

Habitat.--Mediterranean (Messina); North Atlantic, Canary Islands, Station 354, surface.

7. Acanthostaurus hastatus, Haeckel.

Acanthostaurus hastatus, Haeckel, 1862, Monogr. d. Radiol., p. 397, Taf. xix. fig. 5.

Acanthometra hastata, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 809.

Spines of very different size and form; four equatorial spines cylindrical in the basal half, spear-shaped or lanceolate in the distal half, with thin edges, little longer, but five to eight times as {771}broad as the sixteen smaller spines, which are cylindrical, of equal breadth throughout their whole length, with bifid apex. Base of all twenty spines pyramidal, without leaf-cross. Central capsule yellow, spherical, or lenticular.

Dimensions.--Length of the four major spines 0.066, breadth in the middle 0.005, on the apex 0.008; length of the sixteen smaller spines 0.054, breadth 0.001.

Habitat.--Mediterranean (Messina), surface.

Subgenus 2. Staurolithium, Haeckel, 1862, Monogr. d. Radiol., p. 401.

Definition.--All twenty spines in the centre melted and grown together, forming one single, star-like piece of acanthin.

8. Acanthostaurus cruciatus, Haeckel.

Staurolithium cruciatum, Haeckel, 1862, Monogr. d. Radiol., p. 401, Taf. xx. fig. 6.

Astrolithium cruciatum, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 811.

Spines cylindrical, of equal breadth throughout their whole length. Apex simple conical. Four equatorial spines twice as long and broad as the sixteen other spines. All twenty spines in the centre melted and grown together, forming a single piece of acanthin. Central capsule spherical, red-brown, opaque.

Dimensions.--Length of the four equatorial spines 0.12, breadth 0.006; length of the sixteen smaller spines 0.06, breadth 0.003.

Habitat.--Mediterranean (Messina), surface.

Genus 335. Belonostaurus,[375] n. gen.

Definition.--#Quadrilonchida# with four equatorial spines of equal size and form, which are much larger than the sixteen other spines. Eight tropical and eight polar spines very different. No apophyses.

The genus Belonostaurus differs from the preceding Acanthostaurus in the unequal size and form of the eight tropical and the eight polar spines; the latter are much smaller than the former and often quite rudimentary, so that the skeleton appears composed only of twelve spines, four larger equatorial and eight smaller tropical spines. The central bases of the polar spines are constantly preserved. The central capsule is a flattened square disk.

1. Belonostaurus quadratus, n. sp.

Four equatorial spines little compressed, almost cylindrical in the basal half, lanceolate, broader, with simple apex in the distal half. Eight tropical spines a little shorter, but only half as broad, {772}sword-shaped, two-edged, of equal breadth, with simple apex. Eight polar spines very short, conical, also with simple apex. Base without leaf-cross, a simple pyramid.

Dimensions.--Length of the four equatorial spines 0.18, of the eight tropical spines 0.14, of the eight polar spines 0.04.

Habitat.--Central Pacific, Station 271, surface.

2. Belonostaurus bicuspis, n. sp.

Four equatorial spines compressed, almost lanceolate in the basal half, bifid, with two large, bent, little divergent horns in the distal half. Eight tropical spines nearly of the same form, but only half as large, with much smaller horns. Eight polar spines rudimentary, very short, conical, with simple apex. Base with a large leaf-cross.

Dimensions.--Length of the four equatorial spines 0.2, of the eight tropical spines 0.1, of the eight polar spines 0.02.

Habitat.--Central Pacific, Station 263, surface.

Genus 336. Lonchostaurus,[376] Haeckel, 1862, Monogr. d. Radiol., p. 397 (sensu emendato).

Definition.--#Quadrilonchida# with four equatorial spines of unequal size and form; the principal spines (in the longitudinal axis) larger than the lateral spines (in the transverse axis); both opposite spines of each pair equal. Sixteen other spines much smaller (often the eight tropical larger than the eight rudimentary polar spines). No apophyses.

The genus Lonchostaurus differs from the two preceding genera in the unequal size and shape of both equatorial pairs of spines, whilst the two opposite spines of each pair are equal. Therefore the equatorial plane is here a rhombus, not a square, as in the preceding genera. We encounter here for the first time the differentiation of the two equatorial axes, the longitudinal (or hydrotomical) and the transverse (or geotomical) axis. The sixteen other spines are constantly smaller (often also the eight polar more or less rudimentary).

1. Lonchostaurus rhomboides, n. sp. (Pl. 131, fig. 6).

Four equatorial spines cylindrical, twice to three times as broad as the sixteen smaller spines, conical at the distal apex; the two opposite spines of the longitudinal axis twice as long as those of the transverse axis. Sixteen smaller spines conical at the base, with simple bristle-shaped apex. The surface of the rhombical calymma, including the spines, was covered in the figured specimen with small plates like those of Sphærocapsa.

Dimensions.--Length of the cross (longitudinal axis) 0.24, breadth (transverse axis) 0.12.

Habitat.--South Pacific, Station 302, depth 1450 fathoms.

{773}2. Lonchostaurus lanceolatus, n. sp.

Four equatorial spines compressed, lanceolate, tapering equally from the middle towards the two ends; the two opposite spines of the longitudinal axis one and a half times as long as those of the transverse axis. Sixteen smaller spines compressed, linear, two-edged, half as long and only one-fourth as broad as the two longitudinal spines.

Dimensions.--Length of the equatorial cross 0.3, breadth 0.2.

Habitat.--Central Pacific, Station 272, surface.

3. Lonchostaurus bifidus, n. sp.

Four equatorial spines compressed, nearly rectangular, forked, with two long and thin, bent, little divergent horns; the two opposite spines of the longitudinal axis about one-third longer and broader than those of the transverse axis. Sixteen smaller spines of the same form, also forked, but the eight tropical only half as large, and the eight polar spines scarcely one-fourth as large as the two longitudinal spines.

Dimensions.--Length of the equatorial cross 0.36, breadth 0.26.

Habitat.--South-west Pacific, Station 166, surface.

4. Lonchostaurus bifurcus, n. sp. (Pl. 131, fig. 4).

Four equatorial spines nearly rhomboidal, about one and a half times as large as the eight tropical and three times as large as the eight polar spines; the two opposite spines of the longitudinal axis only with two large divergent straight horns; the two spines of the transverse axis somewhat shorter, with four short horns (the two outer horns longer than the two inner). Eight tropical spines doubly forked, each with four thin bristle-shaped horns. Eight polar spines very short, each with two thin bristle-shaped, much divergent horns.

Dimensions.--Length of the equatorial cross 0.34, breadth 0.28.

Habitat.--North-west Pacific, Station 236, surface.

5. Lonchostaurus rhombicus, n. sp.

Four equatorial spines nearly rhomboidal, tapering from the broader middle towards the two ends. Leaf-cross of their base very large. The two opposite spines of the longitudinal axis about one-third larger than the two spines of the transverse axis. Eight tropical spines of the same form, but only half as large. Eight polar spines rudimentary, very short, conical.

Dimensions.--Length of the equatorial cross 0.4, breadth 0.3.

Habitat.--North Pacific, Station 253, surface.

6. Lonchostaurus crystallinus, n. sp. (Pl. 131, fig. 5).

Four equatorial spines lanceolate or rhomboidal, with broad leaf-cross at the base, of a peculiar crystalline structure and a lamellated surface, both opposite spines of the longitudinal axis twice as {774}large as the two spines of the transverse axis. Eight tropical spines of similar form, but only half as large, and with a very large, extremely prominent, lamellated leaf-cross. Eight polar spines quite rudimentary, scarcely prominent.

Dimensions.--Length 0.36, breadth 0.2.

Habitat.--Central Pacific, Station 271, surface.

Genus 337. Zygostaurus,[377] n. gen.

Definition.--#Quadrilonchida# with four equatorial spines of unequal size and form; both lateral spines (in the transverse axis) equal; but both principal spines (in the longitudinal axis) very different, the frontal larger than the caudal. Sixteen other spines much smaller (often the eight tropical larger than the eight rudimentary polar spines). No apophyses.

The genus Zygostaurus differs from all other Staurolonchida in the peculiar differentiation of the four equatorial spines; the two opposite spines of the hydrotomical or longitudinal axis being very different in size and form (the frontal spine forked, the caudal spine simple); whilst the two opposite spines of the geotomical or lateral axis (perpendicular to the former) are equal, forked, but different in shape from the former. Therefore the geometrical fundamental form of the body in this remarkable genus becomes "amphithect" or "bilateral" in the widest signification of this term (comp. my General Morphology, vol. i. pp. 480, 482). Of the three different dimensive axes one (the longitudinal) exhibits unequal poles, whilst the two other (the sagittal and lateral) axes exhibit equal poles.

1. Zygostaurus amphithectus, n. sp. (Pl. 131, fig. 7).

Frontal spine (_c_1) little different from the two lateral spines; each with two divergent curved horns, which are equal and of about the same length as the simple broad basal part. Caudal spine (_c_3) simple, spindle-shaped, about as long as the frontal spine. Tropical spines little smaller than the three former, and of the same symmetrical forked form. Eight polar spines much smaller, but also forked, with thin bristle-shaped branches.

Dimensions.--Length of the cross (longitudinal axis) 0.5, breadth (lateral axis) 0.4.

Habitat.--Central Pacific, Station 272, surface.

2. Zygostaurus longicornis, n. sp.

Frontal spine (_c_1) little different from the two lateral spines, each with two divergent curved horns, which are equal and of about the same length as the simple broad basal part. Caudal {775}spine (_c_3) simple, lanceolate, shorter than the frontal spine. Eight tropical spines in the basal part smaller than the three former, but with much longer fork-branches, which are prolonged into very thin and long bristles. Eight polar spines rudimentary, very short.

Dimensions.--Length of the equatorial cross 0.4, breadth 0.3.

Habitat.--South Pacific, Station 295, surface.

3. Zygostaurus cornutus, n. sp.

Frontal spine (_c_1) little different from the two lateral spines, each with two divergent straight horns, which are shorter than the basal part. Caudal spine (_c_3) simple, triangular, shorter than the three former. Eight tropical spines of equal size and form, doubly forked, each with four thin, bristle-shaped, little divergent teeth. Eight polar spines short, simply forked.

Dimensions.--Length of the equatorial cross 0.5, breadth 0.4.

Habitat.--Indian Ocean (Madagascar), Rabbe, surface.

4. Zygostaurus caudatus, n. sp.

Frontal spine (_c_1) very different from the others, pincer-shaped, with two long, nearly parallel slightly bent horns. Lateral spines (_c_2 and _c_4) only half as long, with two short, nearly parallel horns. Caudal spine (_c_3) very long and stout, spindle-shaped, about twice as long as the frontal spine. Eight tropical spines of equal size and form, symmetrical, with two long and thin, divergent horns. Eight polar spines short and stout, with two divergent horns.

Dimensions.--Length of the equatorial cross 0.8, breadth 0.3.

Habitat.--Central Pacific, Station 265, surface.

5. Zygostaurus frontalis, n. sp.

Frontal spine (_c_1) very different from the others, with two very long, divergent, stout branches. Lateral spines (_c_2 and _c_4) only half as long, each with two stout, nearly parallel horns of equal length. Caudal spine (_c_3) simple, sword-like, shorter than the three former. Eight tropical spines of equal size and form, symmetrical, of the same shape as the two lateral, but only half as large. Eight polar spines very small, rudimentary, each with two short teeth.

Dimensions.--Length of the equatorial cross 0.7, breadth 0.5.

Habitat.--Central Pacific, Station 274, surface.

6. Zygostaurus sagittalis, n. sp. (Pl. 131, fig. 8).

Frontal spine (_c_1) very different from the others, with two equal, strongly divergent, bent horns. Lateral spines (_c_2 and _c_4) little smaller, but with two very unequal horns (the anterior shorter than the posterior). Caudal spine (_c_3) simple, sword-like or triangular, two-edged, longer {776}than the frontal spine. Eight tropical spines different, the four anterior (_b_1, _b_4, _d_1, _d_4) smaller, with longer horns; the four posterior (_b_2, _b_3, _d_2, _d_3) broader, with shorter horns; the anterior horn of each tropical spine is longer than the posterior. Eight polar spines rudimentary, simple, very short.

Dimensions.--Length of the equatorial spine-cross 0.6, breadth 0.4.

Habitat.--Central Pacific, Station 271, surface.

Subfamily 2. LITHOPTERIDA, Haeckel.

Definition.--#Quadrilonchida# with two opposite transverse apophyses either on all twenty spines or only on a part of them.

Genus 338. Quadrilonche,[378] n. gen.

Definition.--#Quadrilonchida# with two simple opposite apophyses either on each radial spine or only on a part of the twenty spines.

The genus Quadrilonche is the ancestral form of the Lithopterida, or of those Quadrilonchida which bear two opposite apophyses or transverse processes. In Quadrilonche these apophyses are simple, whilst they are branched in Xiphoptera and fenestrated in Lithoptera. Each of these three genera may be divided into three subgenera; in the first only the four equatorial spines are provided with apophyses, in the second twelve spines (four equatorial and eight tropical), in the third subgenus all twenty spines.

Subgenus 1. Quadriloncharium, Haeckel.

Definition.--Four large equatorial spines provided with transverse apophyses; sixteen other smaller spines simple, without apophyses.

1. Quadrilonche tetrastaura, n. sp.

Four equatorial spines very large, compressed, two-edged, each crossed in the distal third by two opposite simple apophyses. Sixteen other spines also compressed, linear, somewhat shorter than the former and only half as broad, without apophyses.

Dimensions.--Length of the four major spines 0.12, breadth 0.02; length of the sixteen minor spines 0.08, breadth 0.01.

Habitat.--Central Pacific, Station 266, surface.

{777}2. Quadrilonche platystaura, n. sp. (Pl. 131, fig. 2).

Four equatorial spines lanceolate, compressed, with two opposite triangular simple apophyses in the broadest middle part. Sixteen other spines also lanceolate, much smaller, of about half the length, but only of one-fourth the breadth, without apophyses.

Dimensions.--Length of the four major spines 0.2, breadth 0.018; length of the sixteen minor spines 0.1, breadth 0.004.

Habitat.--North Pacific, Station 235, surface.

Subgenus 2. Quadrilonchidium, Haeckel.

Definition.--All twenty spines provided with transverse apophyses.

3. Quadrilonche mesostaura, n. sp. (Pl. 131, fig. 1).

Four equatorial spines almost of the some form and length as the sixteen others, but of double or triple the breadth; each spine in its middle third with two opposite broad triangular apophyses, in the basal third rectangular, compressed, in the distal third isosceles triangular, with simple apex.

Dimensions.--Length of the four major spines 0.16, breadth 0.01 to 0.015; length of the sixteen minor spines 0.12, breadth 0.005.

Habitat.--Tropical Atlantic, Station 345, surface.

4. Quadrilonche telostaura, n. sp.

Four equatorial spines one and a half times as long and three times as broad as the sixteen others; all twenty spines cylindrical, of equal breadth throughout their whole length, with simple conical apex; each spine crossed in the distal third by two opposite, simple, conical apophyses.

Dimensions.--Length of the four major spines 0.3, breadth 0.012; length of the sixteen minor spines 0.2, breadth 0.004.

Habitat.--South Atlantic, Station 325, surface.

Genus 339. Xiphoptera,[379] Haeckel, 1881, Prodromus, p. 466.

Definition.--#Quadrilonchida# with two opposite branched (but not latticed) apophyses, either on each radial spine or only on a part of the twenty spines.

The genus Xiphoptera differs from the preceding ancestral genus Quadrilonche in the ramification of the apophyses, which bear perpendicular branches on their distal side. These are therefore parallel to the spine itself. If the branches become united by transverse beams then we get Lithoptera.

{778}1. Xiphoptera tessaractena, n. sp.

Four equatorial spines in the outer third crossed by two opposite transverse apophyses, each of which bears on its distal side two to three branches, perpendicular to the apophysis and parallel to the spine itself. Sixteen other spines much smaller, in the outer third crossed by two simple opposite transverse apophyses.

Dimensions.--Length of the four major spines 0.18, of the sixteen minor 0.05 to 0.1.

Habitat.--North Pacific, Station 238, surface.

2. Xiphoptera dodecactena, n. sp. (Pl. 131, fig. 3).

Four equatorial spines one and a half times to twice as long and broad as the eight tropical spines. These twelve spines have the same form and are crossed in their distal third by two large opposite transverse apophyses, each of which bears on its distal side two to four branches, perpendicular to the apophysis and parallel to the spine. Eight polar spines much smaller than the twelve others, simple, without apophyses. The central capsule of this species exhibited a conical protuberance around the base of each individual spine.

Dimensions.--Length of the twelve larger spines 0.1 to 0.2, of the eight smaller 0.02 to 0.06.

Habitat.--Central Pacific, Station 272, surface.

3. Xiphoptera icosactena, n. sp.

Four equatorial spines about twice as long and four times as broad as the sixteen other spines. All twenty spines crossed in the outer third by two large opposite transverse apophyses, each of which bears on its distal side two to four branches perpendicular to the apophysis and parallel to the spine itself.

Dimensions.--Length of the four equatorial spines 0.26, of the sixteen smaller 0.11 to 0.14.

Habitat.--South Pacific, Station 288, surface.

Genus 340. Lithoptera,[380] J. Müller, 1858, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 155.

Definition.--#Quadrilonchida# with two opposite branched and latticed apophyses, either on each radial spine or only on a part of the twenty spines.

The genus Lithoptera, founded by Johannes Müller in 1858 for the first observed Mediterranean species, Lithoptera fenestrata, differs from all other Quadrilonchida in the fenestrated form of the apophyses, which he compared to the sails of a windmill. This peculiar fenestration is effected by two to four parallel pairs of opposite apophyses, which are crossed by perpendicular branches, parallel to the spine itself. {779}Therefore the wings or lattice-plates have quadrangular meshes and lie in one meridian plane of the spine, not in a tangential plane (as in the Acanthophracta). Commonly the lateral ends of the four broad equatorial wings are so crossed that one lateral corner of each wing lies on the upper, the other corner on the under side of both its neighbours; but sometimes the meeting corners have grown together.

Subgenus 1. Lithopteranna, Haeckel.

Definition.--Four equatorial spines with transverse apophyses; sixteen others (eight tropical and eight polar spines) simple, without apophyses.

1. Lithoptera tetraptera, n. sp. (Pl. 131, fig. 9).

Four equatorial spines spindle-shaped, with latticed apophyses, each crossed by two transverse beams which are connected at equal distances by four rods parallel to the spine (therefore each wing with four square meshes in a single row). Lateral corners of the neighbouring wings not meeting. Sixteen smaller spines (eight tropical and eight polar) simple, conical, without apophyses.

Dimensions.--Diagonal of the square body 0.24; length of the inner square 0.16.

Habitat.--Tropical Atlantic, Station 348, surface.

2. Lithoptera mülleri, Haeckel.

Lithoptera mülleri, Haeckel, 1862, Monogr. d. Radiol., p. 398, Taf. xx. figs. 1, 2.

Four equatorial spines four-edged, with large latticed apophyses, each crossed by three transverse beams, which are connected at irregular distances by eight to twelve rods parallel to the spine (therefore each wing with two rows of rectangular meshes). The wings are placed not perfectly in the equatorial plane, but a little obliquely, so that each wing lies with one lateral corner on the upper, with the other corner on the under side of its neighbours. Sixteen smaller spines simple, thin, cylindrical, without apophyses.

Dimensions.--Diagonal of the square body 0.3; length of the inner square 0.17.

Habitat.--Mediterranean (Messina), surface.

3. Lithoptera lamarckii, n. sp.

Four equatorial spines four-edged, with large latticed apophyses; each crossed by three transverse beams, which are connected at short distances by twelve to sixteen rods parallel to the spine (therefore each wing with two rows of hexagonal or nearly elliptical meshes). Wings placed as in Lithoptera mülleri. Sixteen smaller spines simple, thin, prismatic, without apophyses.

Dimensions.--Diagonal of the square body 0.35; length of the inner square 0.2.

Habitat.--Central Pacific, Station 271, surface.

{780}4. Lithoptera tetragona, n. sp.

Four equatorial spines compressed, four-edged, with large latticed apophyses, each crossed by four transverse beams, which are connected at regular distances by eight to twelve rods parallel to the spine. (Therefore each wing with three rows of square meshes.) Wings placed in the equatorial plane and grown together by their meeting lateral ends, forming a square equatorial girdle of lattice-work. Sixteen smaller spines simple, thin, prismatic, without apophyses.

Dimensions.--Diameter of the square body 0.4; length of the inner square 0.22.

Habitat.--North Pacific, Station 244, surface.

Subgenus 2. Lithopterella, Haeckel.

Definition.--Twelve spines (four equatorial and eight tropical) with transverse apophyses; the eight polar spines simple, without apophyses.

5. Lithoptera quadrata, n. sp. (Pl. 131, fig. 10).

Twelve spines with transverse apophyses; eight (polar) spines simple, small, without apophyses. Four equatorial spines very large and stout, compressed, each crossed by four transverse beams, which are connected by eight to ten rods parallel to the spine (therefore each wing with three rows of irregular rectangular meshes). Wings placed in the equatorial plane and grown together by their meeting lateral ends, forming a square equatorial girdle of lattice-work. Eight tropical spines thin, crossed by a long and thin transverse beam, which bears on its distal side eight to ten rods parallel to the spine.

Dimensions.--Diagonal of the square body 0.35; length of the inner square 0.18.

Habitat.--South Atlantic, Station 326, surface.

6. Lithoptera dodecaptera, n. sp.

Twelve spines with transverse apophyses; eight (polar) spines simple, small, without apophyses. Four equatorial spines very large, quadrangular; each crossed by three transverse beams, which are connected by ten to twelve rods parallel to the spine (therefore each wing with two rows of square meshes). Wings placed as in Lithoptera mülleri. Eight tropical spines much thinner, crossed each by two transverse beams, which are connected by six to eight rods parallel to the spine (therefore each wing with one row of rectangular meshes).

Dimensions.--Diagonal of the square body 0.4; length of the inner square 0.25.

Habitat.--Central Pacific, Station 271, surface.

Subgenus 3. Lithopteromma, Haeckel.

Definition.--All twenty spines with transverse apophyses.

{781}7. Lithoptera darwinii, Haeckel.

Lithoptera darwinii, Haeckel, 1879, Natürl. Schöpfungsgesch., Aufl. vii. p. 706, Taf. xvi. fig. 12.

All twenty spines with transverse apophyses; these are quite simple in the eight small cross-shaped polar spines; also simple, but bearing some perpendicular rods, in the eight thin tropical spines. Four equatorial spines very large and stout, each crossed by four transverse beams, which are connected by eight to ten rods parallel to the spine (therefore each wing with three rows of irregular rectangular meshes). Wings placed in the equatorial plane and grown partly together by their meeting lateral ends.

Dimensions.--Diagonal of the square body 0.4; length of the inner square 0.2.

Habitat.--South-east Pacific, west coast of Patagonia, Station 302, surface.

8. Lithoptera icosaptera, n. sp.

All twenty spines with transverse apophyses, bearing one to three rows of rectangular meshes; eight polar spines small, each with a single row; eight tropical spines long and thin, each with two parallel rows. Four equatorial spines much larger and thicker, each with three parallel transverse rows of meshes. All twenty wings free, not grown together by their lateral ends.

Dimensions.--Diagonal of the square body 0.48; length of the inner square 0.24.

Habitat.--Indian Ocean, Belligemma, Ceylon (Haeckel), surface.

9. Lithoptera fenestrata, J. Müller.

Lithoptera fenestrata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 154, Taf. xi. fig. 13.

All twenty spines with transverse apophyses, bearing one to three rows of irregular, rectangular meshes; eight polar and eight tropical spines small, each with a single row of meshes (between two parallel transverse beams). Four equatorial spines little larger, each with two rows (between three parallel transverse beams). Central capsule filled up with green pigment.

Dimensions.--Diagonal of the square body 0.3; length of the inner square 0.2.

Habitat.--Mediterranean (Saint Tropez, Nice).

Family XXXVIII. #AMPHILONCHIDA#, Haeckel (Pl. 132).

Acantholonchida (Amphilonchida et Amphilithida), Haeckel, 1881, Prodromus, p. 466.

Definition.--ACANTHARIA with twenty radial spines of very unequal size, disposed according to the law of the Icosacantha; two opposite equatorial spines (in the longitudinal axis) much larger than the eighteen others. No lattice-shell.

The family #Amphilonchida# is distinguished from all other #Acanthometra# by the excessive development of two opposite equatorial spines, which are much larger {782}than the eighteen other spines. In my Monograph (1862, p. 389) I had united all these Acanthonida in a single genus Amphilonche (with ten species). Some species of it are very common and widely distributed; but in general the number of different forms in this family is much smaller than in the two foregoing families.

The two principal spines, which in all Amphilonchida are much larger than the eighteen other spines, characterise the "hydrotomical axis" or the larger equatorial axis. The two other equatorial spines or the "geotomical spines" are much smaller, and commonly of the same size as the eight tropical and the eight polar spines. In the genera Amphilonche and Amphibelone these eighteen smaller spines are rather equally developed; sometimes they are very small or quite rudimentary, so that the skeleton seems to be represented only by the two very long principal spines (Pl. 132, fig. 4). The genus Acantholonche is distinguished by the unequal size of the eight tropical and the eight polar spines, the latter being more or less rudimentary. However, the central bases of all twenty spines, by which they are united in the centre, are constantly present. The genus Amphibelone is distinguished by the unequal size and form of the two principal spines, one of them the "caudal spine," being larger (and often of another form) than the opposite "frontal spine."

The form of the radial spines is in the Amphilonchida far less varied and complicated than in the other Acanthonida (the Astrolonchida and Quadrilonchida). Apophyses or lateral transverse processes are never developed. The three main forms of spines are the same as in the other Acanthonida; they are (1) either cylindrical or conical (like Acanthometron), or (2) compressed or two-edged (like Zygacantha), or (3) quadrangular or four-edged (like Acanthonia). Often the spines are angular in the inner or proximal, roundish in the outer or distal part. The distal apex is commonly simple, conical or pyramidal. The central base is commonly also pyramidal, as in the majority of the Acanthonida; and the triangular faces of the neighbouring bases are simply propped one upon another. More rarely a basal leaf-cross is developed above the basal pyramid. Very rarely the central bases of the united spines grow together in the centre, so that the whole skeleton forms a single piece of acanthin.

The Central Capsule is rarely spherical, commonly prolonged in the direction of the hydrotomical axis; ellipsoidal or cylindrical, sometimes also four-sided prismatic; it commonly envelops the greater part of the two principal spines; its structure and contents are the same as in the other Acanthonida.

Synopsis of the Genera of Amphilonchida.

{ Two opposite large { principal spines Eighteen smaller spines { (frontal and caudal) of nearly equal size { equal, 341. Amphilonche. and similar form. { { Caudal spine larger than { the frontal spine, 342. Amphibelone.

Eight tropical and eight polar spines of different sizes (the latter often rudimentary), 343. Acantholonche.

{783}Genus 341. Amphilonche,[381] Haeckel, 1862, Monogr. d. Radiol., p. 389.

Definition.--#Amphilonchida# with two equal principal spines (frontal and caudal spines not different); the eighteen smaller spines nearly equal.

The genus Amphilonche represents the original and at the same time the most common form of Amphilonchida; the two opposite principal spines are of equal size and form, much larger (and often also of another form) than the eighteen smaller spines; these latter exhibit no marked differences in size and form.

Subgenus 1. Amphiloncharium, Haeckel.

Definition.--Spines in the centre united by triangular faces of their pyramidal bases, propped one upon another. No basal leaf-cross.

1. Amphilonche belonoides, Haeckel.

Amphilonche belonoides, Haeckel, 1862, Monogr. d. Radiol., p. 392, Taf. xvi. fig. 6, Taf. xviii. fig. 21.

Acanthometra belonoides, Haeckel, 1860, Monatsber. d. k. Akad. d. Wiss. Berlin, p. 808.

Two principal spines cylindrical, of equal breadth throughout their whole length, with simple conical apex; base a small pyramid, without leaf-cross. Eighteen smaller spines conical, much shorter, with simple bristle-shaped apex. Central capsule spindle-shaped or cylindrical, yellow.

Dimensions.--Length of the two major spines 0.4 to 0.8, of the eighteen minor 0.05 to 0.2.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

2. Amphilonche lanceolata, n. sp. (Pl. 132, fig. 1).

Two principal spines compressed, lanceolate, two-edged, gradually tapering from the broader middle towards the two ends; apex simple; base a large pyramid, with broad leaf-cross. Eighteen smaller spines about half as long, pyramidal, with simple conical or bristle-shaped apex. Central capsule lentelliptical, pink, opaque.

Dimensions.--Length of the two major spines 0.2, of the eighteen minor 0.1.

Habitat.--Tropical Atlantic, Station 343, surface.

3. Amphilonche diodon, n. sp. (Pl. 132, fig. 3).

Two principal spines compressed, lanceolate, two-edged, tapering from the broader middle towards the two ends; apex simple; base a small pyramid, without leaf-cross. Eighteen smaller spines {784}sword-shaped, only two-thirds or one-half as long, and one-third or one-fourth as broad, each with two opposite teeth in the distal part. Central capsule ellipsoidal.

Dimensions.--Length of the two major spines 0.13, breadth 0.02; length of the eighteen minor spines 0.1.

Habitat.--North Atlantic, Station 352, surface.

4. Amphilonche tenuis, Haeckel.

Amphilonche tenuis, Haeckel, 1862, Monogr. d. Radiol., p. 389, Taf. xvi. fig. 1, Taf. xviii. fig. 16.

Acanthometra tenuis, Haeckel, 1860, Monatsber. d. k. Akad. d. Wiss. Berlin, p. 807.

Two principal spines quadrangular prismatic, with smooth edges, slightly or not at all prominent, of equal breadth throughout their whole length; apex simple or bifid; base a small pyramid, without leaf-cross. Eighteen smaller spines of the same form, but only one-fourth or one-third as long. Central capsule spherical or ellipsoidal, colourless.

Dimensions.--Length of the two major spines 0.2 to 0.3, of the eighteen minor spines 0.05 to 0.1.

Habitat.--Mediterranean (Messina); Atlantic, Station 354, Canary Islands, surface.

5. Amphilonche denticulata, Haeckel.

Amphilonche denticulata, Haeckel, 1862, Monogr. d. Radiol., p. 390, Taf. xvi. fig. 2, Taf. xviii. fig. 17.

Two principal spines quadrangular prismatic, with prominent, elegantly denticulated edges, of equal breadth throughout their whole length; apex simple or truncated; base a small pyramid, without leaf-cross. Eighteen smaller spines of the same form, but only one-fourth or one-third as long. Central capsule ellipsoidal, opaque, yellowish-brown.

Dimensions.--Length of the two major spines 0.3 to 0.4, of the eighteen minor 0.1; breadth of the former 0.009, of the latter 0.006.

Habitat.--Mediterranean (Messina), Haeckel, surface.

6. Amphilonche heteracantha, Haeckel.

Amphilonche heteracantha, Haeckel, 1862, Monogr. d. Radiol., p. 293, Taf. xvi. fig. 7.

Acanthometra heteracantha, Haeckel, 1860, Monatsber. d. k. Akad. d. Wiss. Berlin, p. 808.

Two principal spines quadrangular prismatic, very large, with four broad, prominent, lamellar edges, of equal breadth throughout their whole length. Apex as well as the base a four-sided pyramid. Eighteen smaller spines very thin, conical, with bristle-shaped apex; base a small pyramid, without leaf-cross. Central capsule cylindrical or violin-shaped, opaque yellow.

Dimensions.--Length of the two major spines 0.2 to 0.3, breadth 0.015 to 0.02; length of the eighteen minor spines 0.1 to 0.15, basal breadth 0.004 to 0.008.

Habitat.--Mediterranean (Messina); Central Pacific, Station 271, surface.

{785}7. Amphilonche elongata, Haeckel.

Amphilonche elongata, Haeckel, 1862, Monogr. d. Radiol., p. 392, Taf. xviii. figs. 22_a_, 22_b_.

Acanthometra elongata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 48, Taf. vii. fig. 13.

Two principal spines quadrangular prismatic in the proximal half, cylindrical or spindle-shaped in the distal half, with simple apex; base a small pyramid, without leaf-cross. Eighteen smaller spines very thin, bristle-shaped, conical on the base, with small pyramid. Central capsule spindle-shaped, transparent, yellow.

Dimensions.--Length of the two major spines 0.3 to 0.5, breadth 0.01 to 0.03; length of the eighteen smaller spines 0.05 to 0.3.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

Subgenus 2. Amphilonchidium, Haeckel.

Definition.--Spines at the central base with a broad leaf-cross, composed of four prominent triangular lamellæ; between the meeting edges of the latter twenty-two pyramidal compartments or basal funnels.

8. Amphilonche ovata, Haeckel.

Amphilonche ovata, Haeckel, 1862, Monogr. d. Radiol., p. 390.

Acanthometra ovata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 47, Taf. vii. fig. 10, Taf. ix. fig. 4.

Two principal spines cylindrical, of equal breadth throughout their whole length, with simple conical or bifid apex; base with a large leaf-cross of double the breadth. Eighteen smaller spines of the same form, but thinner and only half as long. Central capsule ellipsoidal, brown, opaque.

Dimensions.--Length of the two major spines 0.3 to 0.4, breadth 0.008 to 0.012; length of the eighteen minor spines 0.1 to 0.2.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

9. Amphilonche conica, n. sp. (Pl. 132, fig. 6).

Two principal spines conical, elongate, with simple apex; base thickened, with large leaf-cross. Eighteen smaller spines also conical, of about the same basal breadth, but only one-fourth to one-half as long. Central capsule ellipsoidal, pellucid.

Dimensions.--Length of the two major spines 0.15 to 0.2, basal breadth 0.03 to 0.04; length of the eighteen minor spines 0.05 to 0.1.

Habitat.--Central Pacific, Stations 265 to 274, surface.

{786}10. Amphilonche lancetta, n. sp.

Two principal spines compressed, lanceolate, two edged, gradually tapering from the broader middle towards the two ends; apex simple; base of double the breadth, with a large leaf-cross. Eighteen smaller spines of the same form, but shorter and only half as broad. Central capsule lentelliptical, pellucid.

Dimensions.--Length of the two major spines 0.2 to 0.3, breadth in the middle part 0.02 to 0.03; length of the eighteen smaller spines 0.1 to 0.2.

Habitat.--South Pacific, Station 288, surface.

11. Amphilonche complanata, Haeckel.

Amphilonche complanata, Haeckel, 1862, Monogr. d. Radiol., p. 390, Taf. xvi. fig. 3, Taf. xviii. fig. 18, a, b.

Acanthometra complanata, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 808.

Two principal spines compressed, two-edged, linear, of equal breadth throughout their whole length; apex emarginate or bifid; base with a large leaf-cross of double the breadth. Eighteen smaller spines of the same form, but only one-fourth to one-half as large. Central capsule ellipsoidal, yellow, pellucid.

Dimensions.--Length of the two major spines 0.15 to 0.25, breadth 0.004 to 0.006; length of the eighteen minor spines 0.05 to 0.1.

Habitat.--Mediterranean (Messina), surface.

12. Amphilonche messanensis, Haeckel.

Amphilonche messanensis, Haeckel, 1862, Monogr. d. Radiol., p. 391, Taf. xvi. fig. 4, Taf. xviii. fig. 19.

Acanthometra messanensis, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 808.

Two principal spines quadrangular prismatic, often a little compressed from two sides, of nearly equal breadth throughout their whole length; apex either truncate or emarginate, with two opposite teeth; base with a large leaf-cross of double the breadth. Eighteen smaller spines of similar form or more compressed, much shorter. Central capsule spherical or ellipsoidal, yellow, transparent.

Dimensions.--Length of the two major spines 0.12 to 0.18, breadth 0.016; length of the minor spines 0.05 to 0.09.

Habitat.--Mediterranean (Messina, Corfu), Haeckel, surface.

13. Amphilonche hydrotomica, n. sp. (Pl. 132, fig. 2).

Two principal spines quadrangular prismatic, with four broad prominent lamellar edges or wings, of equal breadth throughout their whole length; apex pyramidal; base with a large leaf-cross. Eighteen smaller spines cylindrical or bristle-shaped, only half as long and very thin. Central capsule cylindrical or spindle-shaped, very long, opaque.

{787}Dimensions.--Length of the two major spines 0.1 to 0.2, breadth 0.02 to 0.03; length of the eighteen minor spines 0.05 to 0.1.

Habitat.--Central Pacific, Stations 270 to 274, surface.

14. Amphilonche violina, n. sp. (Pl. 132, fig. 5).

Two principal spines quadrangular prismatic, nearly violin-shaped, with four very broad, prominent, lamellar wings, which are constricted in the middle part, and broadened towards the two ends; apex truncate pyramidal; base with a large leaf-cross. Eighteen smaller spines much shorter, of equal breadth at the base, assuming the form of a quadrangular pyramid, thin prismatic in the distal half. Central capsule spindle-shaped, opaque.

Dimensions.--Length of the two major spines 0.15 to 0.18, breadth 0.02 to 0.025; length of the eighteen minor spines 0.04 to 0.08.

Habitat.--Central Pacific, Station 271, surface.

15. Amphilonche tetraptera, Haeckel.

Amphilonche tetraptera, Haeckel, 1862, Monogr. d. Radiol., p. 391, Taf. xvi. fig. 5, Taf. xviii. fig. 20.

Acanthometra tetraptera, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 808.

Two principal spines four-sided pyramidal, with four broad lamellar prominent edges; apex simple or bifid; base with a large leaf-cross. Eighteen smaller spines of similar form, but only half as large. Central capsule spherical, opaque.

Dimensions.--Length of the two major spines 0.2, breadth on the base 0.025; length of the eighteen minor spines 0.1.

Habitat.--Mediterranean (Messina); North Atlantic, Canary Islands, Stations 352 to 354, surface.

Subgenus 3. Amphilithium, Haeckel, 1881, Prodromus, p. 466.

Definition.--Spines in the basal part grown together, so that the whole skeleton represents a single piece of acanthin; a star with two larger and eighteen smaller rays.

16. Amphilonche concreta, n. sp. (Pl. 132, figs. 4, 4_a_).

Two principal spines cylindrical, very long, of equal breadth throughout their whole length, with simple conical apex. Eighteen smaller spines short, conical or bristle-shaped, scarcely one-fourth or one-tenth as long, often quite rudimentary. All twenty spines perfectly grown together in the centre, forming a single piece of acanthin (derived from Amphilonche belonoides by central concrescence; often the sutures of the concreted bases are visible, fig. 4_a_).

Dimensions.--Length of the two major spines 0.1 to 0.4, breadth 0.005 to 0.015; length of the eighteen minor spines 0.005 to 0.15.

Habitat.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

{788}17. Amphilonche acufera, n. sp.

Two principal spines thick, four-sided prismatic in the basal half, cylindrical or spindle-shaped in the distal half, with simple conical apex. Eighteen smaller spines shorter, thin, bristle-shaped or conical on the base. All twenty spines in the centre perfectly grown together, forming a single piece of acanthin. (Derived from Amphilonche elongata by central concrescence.)

Dimensions.--Length of the two major spines 0.3 to 0.5, breadth 0.01 to 0.03; length of the eighteen minor spines 0.08 to 0.2.

Habitat.--Central Pacific, Stations 266 to 274, surface.

Genus 342. Amphibelone,[382] Haeckel, 1862, Monogr. d. Radiol., p. 392.

Definition.--#Amphilonchida# with two unequal principal spines (the frontal spine very different from the caudal spine); the eighteen smaller spines nearly equal.

The genus Amphibelone exhibits among the Amphilonchida the same remarkable differentiation of the two principal or longitudinal spines, as Zygostaurus among the Quadrilonchida; the frontal spine differs commonly from the caudal spine not only in its size, but also in its peculiar form; commonly one pole of the longitudinal axis is much more strongly developed than the other. The eighteen smaller spines are nearly equal.

Subgenus 1. Amphibelonium, Haeckel.

Definition.--All twenty spines separate, but in contact in the centre and resting one against another by the triangular sides of their pyramidal bases, without a prominent basal leaf-cross.

1. Amphibelone aciculata, n. sp.

Two principal spines thick, without edges and wings, the frontal spine short, spindle-shaped, the caudal three to six times as long, cylindrical, both of equal breadth, with simple conical apex and simple pyramidal base, without leaf-cross. Eighteen smaller spines very thin, bristle-shaped, of the same length as the frontal spine. Central capsule cylindrical or spindle-shaped, enveloping the two principal spines nearly throughout their whole length.

Dimensions.--Length of the frontal spine 0.2 to 0.4, of the caudal spine 1.0 to 2.0; breadth of both 0.01; length of the eighteen smaller spines 0.1 to 0.3.

Habitat.--South Atlantic, Station 325, surface.

{789}2. Amphibelone cultellata, n. sp. (Pl. 132, fig. 10).

Two principal spines broad, two-edged, knife-shaped; two opposite in the equatorial plane, thin and broad wings or lamellæ are developed, and these enclose the proximal part of both spines, whilst their distal part is free, cylindrical, with conical apex: the two wings of the longer caudal spine are lanceolate, twice to four times as broad as the two wings of the shorter frontal spine; their base is a simple pyramid without leaf-cross. Eighteen smaller spines conical, with bristle-shaped prolongation, one-fourth to one-half as long as the frontal spine. Central capsule green, semitransparent.

Dimensions.--Length of the frontal spine 0.1 to 0.2, breadth 0.02 to 0.03; length of the caudal spine 0.2 to 0.4, breadth 0.04 to 0.08; length of the eighteen smaller spines 0.05 to 0.15.

Habitat.--Indian Ocean, Maldive Islands (Haeckel), surface.

3. Amphibelone pyramidata, n. sp. (Pl. 132, fig. 9).

Two principal spines four-winged, with four crossed, very thin and broad wings, which are somewhat broader in the convex middle part than at either end; both ends of each spine four-sided pyramidal, with four concave edges and a very small terminal pyramid; base without leaf-cross. The longer caudal spine is twice as broad at the distal end as at its proximal end, and three times as broad as the distal end of the shorter frontal spine. Eighteen smaller spines bristle-shaped, with four-sided pyramidal bases. Central capsule pyramidal, enveloping the two principal spines throughout their whole length; the base of the slender quadrangular pyramid is on the caudal, the apex on the frontal pole of the longitudinal axis.

Dimensions.--Length of the frontal spine 0.2 to 0.25, distal breadth 0.01; length of the caudal spine 0.3 to 0.4, distal breadth 0.03; length of the eighteen smaller spines 0.04 to 0.08.

Habitat.--Cape of Good Hope, Station 143, depth 1900 fathoms.

4. Amphibelone anomala, Haeckel.

Amphilonche anomala, Haeckel, 1862, Monogr. d. Radiol., p. 394, Taf. xvi. fig. 8, Taf. xviii. figs. 23_a_, 23_b_.

Acanthometra anomala, Haeckel, 1860, Monatsber. d. k. Akad. d. Wiss. Berlin, p. 808.

Two principal spines four-winged, nearly prismatic, with four crossed, very broad and thick wings; both ends of each spine four-sided pyramidal, with four concave edges and a very small terminal pyramid; base without leaf-cross. The edges of the four wings are concave on the shorter frontal, convex on the longer caudal spine. Eighteen smaller spines only one-fourth to one-half as long, linear, two-edged, with two parallel teeth on the distal end. Central capsule four-sided prismatic, olive-green, enveloping almost completely the two principal spines.

Dimensions.--Length of the frontal spine 0.12, middle breadth 0.016; length of the caudal spine 0.14, middle breadth 0.024; length of the eighteen smaller spines 0.04 to 0.06.

Habitat.--Mediterranean (Messina), surface.

{790}Subgenus 2. Amphibelithium, Haeckel.

Definition.--All twenty spines grown together in the centre, forming a single star-shaped piece of acanthin.

5. Amphibelone clavaria, n. sp.

Two principal spines roundish, without edges and wings; the smaller frontal spine elongate conical, the larger caudal spine two to four times as long, cylindrical, in the distal part spindle-shaped or club-shaped, with conical apex. Central base simple pyramidal, without leaf-cross. Eighteen smaller spines much shorter, bristle-shaped. Central capsule very long, club-shaped. All twenty spines perfectly grown together in the centre.

Dimensions.--Length of the frontal spine 0.12, of the caudal spine 0.4 to 0.8; frontal breadth 0.01, caudal breadth 0.03; length of the eighteen smaller spines 0.05.

Habitat.--Central Pacific, Station 272, surface.

Genus 343. Acantholonche,[383] Haeckel, 1881, Prodromus, p. 466.

Definition.--#Amphilonchida# with two equal principal spines (frontal and caudal spines not different). The eighteen smaller spines are very unequal, ten of them (eight tropical and two transverse equatorial spines) much larger than the rudimentary eight polar spines.

The genus Acantholonche differs from its ancestral genus Amphilonche in the different shape of the eight tropical and the eight polar spines; these latter are much smaller than the former, which are almost equal to the two transverse equatorial spines. The two principal spines are equal, but in size and shape very different from the others.

1. Acantholonche amphipolaris, n. sp. (Pl. 132, fig. 7).

Two principal spines stout, quadrangular prismatic in the basal half, cylindrical or spindle-shaped in the distal half, with simple conical apex; base a small pyramid without leaf-cross. Two transverse and eight tropical spines, about half as long as the former, very thin, bristle-shaped, conical at the basal part. Eight polar spines very small, scarcely one-eighth or one-fourth as long as the latter, short pyramidal or conical, often quite rudimentary. Central capsule cylindrical, enveloping the basal half of the two principal spines.

Dimensions.--Length of the two principal spines 0.4 to 0.5, of the ten smaller spines 0.2 to 0.3, of the eight rudimentary polar spines 0.01 to 0.06; breadth of the two large spines 0.02 to 0.03.

Habitat.--Central Pacific, Stations 266 to 274, surface.

{791}2. Acantholonche peripolaris, n. sp. (Pl. 132, fig. 8).

Two principal spines quadrangular prismatic, with four broad prominent lamellar wings, of increasing breadth towards the pyramidal distal apex. Both ends of each spine four-sided pyramidal, base without leaf-cross. Two transverse and eight tropical spines about two-thirds as long as the former, four-sided pyramidal in the basal half, conical in the distal half, often curved. Eight polar spines very small, about one-fourth as long as the latter, short conical or pyramidal. Central capsule four-sided prismatic, enveloping both principal spines.

Dimensions.--Length of the two principal spines 0.2, of the ten smaller spines 0.12, of the eight rudimentary polar spines 0.04.

Habitat.--Central Pacific, Station 274, surface.

----

Order IV. ACANTHOPHRACTA, Richard Hertwig, 1879.

Acanthometræ cataphractæ, Johannes Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, pp. 12, 22, 49. Dorataspida et Diploconida, Haeckel, 1862, Monogr. d. Radiol., pp. 404, 412. Acanthophractida, Richard Hertwig, 1879, Organismus d. Radiol., pp. 25, 137. Dorataspida, Diploconida, et Sphærocapsida, Haeckel, 1881, Prodromus, p. 467.

Definition.--ACANTHARIA with complete latticed shell.

The order #Acanthophracta#, the fourth order of Radiolaria, comprises all those ACANTHARIA in which the acanthinic skeleton is a complete latticed or fenestrated shell, supported by radial spines arising from one common central point. By the possession of such a complete shell the #Acanthophracta# differ from their ancestral group, the nearly allied #Acanthometra#, which represent the older and simpler, first order of ACANTHARIA. All #Acanthophracta# are Icosacantha (like the #Acanthonida#, their ancestral group), and possess twenty radial spines disposed according to the Müllerian law (compare above, p. 717).

Johannes Müller, who first observed five representatives of this order, called a part of them "Acanthometræ cataphractæ," and united these with the true #Acanthometra# (Acanthometra costata and Acanthometra cataphracta; Abhandl. d. k. Akad. d. Wiss. Berlin, 1858, pp. 12, 49). Another part was united by him with the true Haliomma (Haliomma echinoides, Haliomma hystrix, Haliomma tabulatum; Abhandl. d. k. Akad. d. Wiss. Berlin, 1858, pp. 36, 37). He supposed that these latter formed the immediate transition from the true #Acanthometra# to the true Haliomma, and that their skeleton was siliceous.

{792}In my Monograph (1862, p. 412) I founded a separate subfamily, Dorataspida, for the "Acanthometræ cataphractæ," which I considered as the first subfamily of the "Ommatida." That subfamily contained at that time only two genera, Dorataspis (with seven species) and Haliommatidium (with five species). A third genus, Aspidomma (with two species), was united by me with the Haliommatida (because of its double shell). For a fourth genus (Diploconus) with a single species I founded the peculiar family of Diploconida. Therefore the whole number of #Acanthophracta# described in my Monograph amounted only to four genera and fifteen species. Now the rich collections of the Challenger have added such a great number of new forms, that we may distinguish here thirty-eight genera and two hundred and twelve species.

Richard Hertwig in his excellent work (Der Organismus der Radiolarien, 1879, p. 25) separated his "Acanthophractida" perfectly from the "Ommatida" (or the siliceous #Sphæroidea#), and united them with the "Acanthometrida" in his order "Acanthometrea." But he separated them also from the nearly allied Diploconida, following my former arrangement. He distinctly noted that the skeleton in all these Acanthophractida (as well as in the Acanthometrida) consists not of silex but of the organic substance "acanthin."

The astonishing number of new and interesting forms of #Acanthophracta# which I have found in the rich collection of the Challenger enables me to distinguish now in this suborder six different families, two of which are perfectly new (the Sphærocapsida and the Hexalaspida). But the four other families also are so much enlarged that their interesting morphology appears in quite a new and clear light. Far the largest and most important of these six families is that of the true Dorataspida, which embraces seventeen genera and one hundred and eight species (more than the other five families together). From this largest and oldest ancestral family four other families have afterwards arisen, whilst a single family, the Sphærocapsida, seems to possess no direct phylogenetic connection with the five other families.

The peculiar and quite new family of Sphærocapsida (Pl. 133, figs. 7-11; Pl. 135, figs. 6-10) differs from all other #Acanthophracta# in the singular structure of the spherical acanthinic shell, composed of innumerable small plates or aglets, each of which is pierced by a very small porule. This peculiar pavemented shell (enclosing the central capsule and separated from it by the jelly-like calymma) seems to be produced on the surface of the spherical calymma, immediately by secretion of the pseudopodia, and independently from the twenty radial spines, united in the centre of the sphere. On the twenty points, where the spines perforate the shell, there are originally eighty larger pores (four around each piercing spine); but there is no certain indication that the shell is produced by the meeting apophyses of the twenty spines, as is the case in the five other families of #Acanthophracta#. Therefore perhaps it is {793}more natural to unite these latter into another suborder as #Cladophracta#, and to separate them from the Sphærocapsida, which may be called Capsophractæ.

The Dorataspida (Pls. 134-138), the common ancestral stock of the #Cladophracta#, in the definition here restricted embraces all those #Acanthophracta# in which the spherical lattice-shell is simple and composed of the meeting branches of twenty radial spines united in its centre. As already pointed out above, this family is probably diphyletic, and embraces two subfamilies which have been derived originally from two different forms of #Acanthonida#--the Diporaspida (with two opposite apophyses on each spine) derived from the Phractacanthida, and the Tessaraspida (with four crossed apophyses on each spine) derived from the Stauracanthida; in the former we find originally forty apophyses, in the latter eighty apophyses, by the meeting branches of which the spherical lattice-shell originates. The four following families of #Acanthophracta# have probably been derived from the Diporaspida.

The Phractopeltida (Pl. 133, figs. 1-6) differ from all other #Acanthophracta# in the possession of a double lattice-shell, composed of two concentric spheres which are united by the twenty radial spines meeting in the centre. As all Phractopeltida possess originally only two apophyses on each radial spine, they must be derived from the Diporaspida (Orophaspis), and bear to them the same relation as the Dyosphærida do to the Monosphærida. As the spherical central capsule of the Phractopeltida is enclosed between both shells, smaller than the outer, larger than the inner shell, the latter may be called "medullary shell," the former "cortical shell." This family represents among the #Acanthophracta# only the "Diplophracta," whilst all others are "Haplophracta."

The three families here characterised may be called together "#Sphærophracta#," as their central capsule and the enveloping shell are constantly spherical (or the shell sometimes an "endospherical polyhedron"). On the contrary the following three families of #Acanthophracta# may be united as "#Prunophracta#," as their central capsule and shell are never spherical, but either ellipsoidal or lenticular or of another form. The common ancestral stock of this suborder are the Belonaspida, in which the form of the central capsule and the enclosing lattice-shell is ellipsoidal; they are derived from the Dorataspida (and probably all from the subfamily Diporaspida) by the prolongation of two opposite radial spines which are larger than the eighteen others; they are the two equatorial spines of the "hydrotomical axis" (compare above, p. 719, and Pl. 136, figs. 6-9).

The Hexalaspida (Pl. 139) represent a new and very remarkable family, distinguished from all other #Acanthophracta# by the preponderating development of six stout radial spines, which are much larger than the fourteen others. These six principal spines lie in one meridian plane of the shell (in the "hydrotomical plane," p. 720), and are the two opposite equatorial spines and the four appertaining polar spines of the same plane. {794}As the fourteen smaller spines develop their apophyses at smaller distances from the centre, the shell assumes a peculiar lenticular or discoidal form, and the margin of this disk bears the six larger spines. Moreover the enclosed small central capsule is lenticular. The Hexalaspida may be derived immediately from the Belonaspida.

The Diploconida (Pl. 140) form the last and the most modified family of all #Acanthophracta#. The remarkable shell exhibits the strange form of a double cone, bearing in its axis two very large opposite spines; these are the two equatorial spines of the "hydrotomical axis" (p. 719). The double-conical or nearly cylindrical shell is composed of three different parts or segments; the small middle part is the true lattice-shell of the Hexalaspida and Belonaspida, and bears the eighteen smaller (often quite rudimentary) radial spines. The two other parts (opposite on both poles of its hydrotomical axis) are the conical or cylindrical, solid, basal sheaths of the two large equatorial spines, enveloping their major part. In consequence of this peculiar metamorphosis of the shell the Diploconida represent the last and the most aberrant group of all ACANTHARIA.

Synopsis of the Suborders and Families of #Acanthophracta#.

------------------------------------------------------------------------- Suborder I. SPHÆROPHRACTA. Twenty radial spines of equal size. Shell spherical (or an endospherical polyhedron). ------------------------------------------------------------------------- Shell spherical, simple, pierced by twenty or eighty aspinal pores and composed of a pavement of innumerable very small plates or aglets, each pierced by one porule, 1. SPHÆROCAPSIDA.

Shell spherical, simple, composed of the meeting branches of two or four apophyses of the twenty radial spines, 2. DORATASPIDA.

Shell spherical, double, composed of two concentric lattice-spheres, which are connected by the twenty radial spines and composed of the meeting branches of their apophyses, 3. PHRACTOPELTIDA. ------------------------------------------------------------------------- Suborder II. PRUNOPHRACTA. Twenty radial spines of unequal size; two or six hydrotomical spines much larger than the eighteen or fourteen others. Shell not spherical. ------------------------------------------------------------------------- Shell ellipsoidal, with prolonged hydrotomical axis, the two spines of which are larger than the eighteen others, 4. BELONASPIDA.

Shell lenticular or discoidal, with six larger spines placed in the hydrotomical plane (fourteen other spines much smaller), 5. HEXALASPIDA.

Shell diploconical or nearly cylindrical, with two opposite large funnels, the sheaths of the enlarged two spines of the hydrotomical axis (eighteen other spines much smaller or rudimentary), 6. DIPLOCONIDA.

{795}----

Suborder I. SPHÆROPHRACTA, Haeckel.

Definition.--Shell spherical, with twenty radial beams of equal size.

Family XXXIX. #SPHÆROCAPSIDA#, Haeckel (Pl. 133, figs. 7-11; Pl. 135, figs. 6-10).

Sphærocapsida, Haeckel, 1881, Prodromus, p. 469.

Definition.--ACANTHARIA with simple spherical porous shell, composed of innumerable very small plates, each of which is pierced by one radial porule. Twenty radial spines of equal size meeting in the centre of the shell and disposed according to the Müllerian law of the Icosacantha, sometimes short and enclosed in the shell, at other times long and piercing it (rarely rudimentary or quite absent). Shell pierced therefore either by twenty larger perspinal pores or by eighty smaller aspinal pores. Central capsule spherical, enclosed in the porous shell.

The family #Sphærocapsida#, founded by me in 1881 for the single genus Sphærocapsa, represents a very peculiar and remarkable group of the #Acanthophracta#, very different from the five other families of this suborder, and probably derived, independently of them, directly from the #Acanthonida#. Whilst the lattice-shell of the five other families is composed of the meeting branches of lateral apophyses of the twenty spines, and its meshes are all or partly the intervals between these apophyses, in the Sphærocapsida the spherical shell has quite another structure, and is composed of innumerable small plates (each with one pore) which are secreted on the surface of the spherical calymma, independently of the twenty radial spines, which do not possess true apophyses.

In all Sphærocapsida the structure of the spherical shell is quite peculiar and different from that of all other Radiolaria. It is composed everywhere of innumerable very small plates or aglets, which are connected irregularly like paving-stones, and form a single continuous layer or pavement on the surface of the spherical calymma (Pl. 133, fig. 11, a; Pl. 135, figs. 8, 10). The small plates or paving-stones, which we will call "aglets," are connected at their meeting edges by a kind of cement, and form together with it a continuous thick capsule of acanthin. The form of the aglets is commonly more or less irregular, roundish or polygonal, sometimes longish (Pl. 133, fig. 11, a), more rarely it becomes rather regular, hexagonal, square, or roundish (Pl. 135, fig. 8). Usually all aglets of one and the same individual are of nearly equal size, between 0.01 and 0.02 in diameter, rarely less or more. The outer face of the aglets is more or less concave, so that the elevated meeting edges of the neighbouring aglets commonly form together a prominent network of crests (Pl. 135, figs. 8, 10); rarely the meeting edges partly cover one another like squamules (Pl. 133, fig. 11, a). {796}Each small plate or aglet is pierced in its centre by a single radial canalicule or porule. The dimpled surface, so produced, resembles somewhat the dimpled plates of Ceriaspis, &c. Different from these innumerable very small dimples of the surface are the twenty larger "spinal dimples," or the concave larger plates, which are originally pierced by the twenty radial spines. Before we describe these, we must examine the spines themselves.

The twenty radial spines of all observed Sphærocapsida (sixteen species) agree perfectly with those of the genus Acanthonia (p. 749), and especially with Acanthonia tetracopa, Acanthonia denticulata, &c. All twenty spines, regularly disposed according to the Müllerian law of the Icosacantha, are of equal size, constantly four-edged prismatic, of equal breadth throughout their whole length. The prominent four edges are parallel, sometimes smooth, at other times elegantly denticulated. The central bases of the twenty spines are pyramidal, without leaf-cross, and propped one upon another with their triangular faces, as in the majority of the #Acanthonida#.

The relation of the twenty radial spines to the spherical shell exhibits in the five genera described very peculiar and important differences. In the first described genus, in Sphærocapsa, the spines are exactly as long as the shell-radius, and therefore are not prominent over the surface of the shell, with which they are firmly connected; the truncated distal end of the spine lies therefore here in the surface of the shell itself, and is connected with it by its four edges, between which four open aspinal pores remain, as in Tessaraspis, &c. (Pl. 135, figs. 6-10). In the next allied genus, Astrocapsa (Pl. 133, figs. 9, 10), the spines are longer than the shell-radius, and therefore more or less prominent over its surface; the piercing part of each spine is also surrounded by four aspinal pores. In the two following genera, Porocapsa and Cannocapsa (Pl. 133, figs. 7, 8), the radial spines are shorter than the shell-radius and therefore quite hidden and withdrawn inside the shell, which they do not reach. But in the ideal prolongation of each spine the shell is pierced by a single large opening, the "perspinal pore" or "perspinal hole," composed of the four united aspinal pores. Whilst in Porocapsa the perspinal pores are simple, they are prolonged in Cannocapsa into cylindrical tubes, open at both ends. The twenty perspinal holes of these Porocapsida are therefore derived by confluence of the eighty original aspinal pores of the Astrocapsida and preserve the same regular disposition, according to the Müllerian law of the Icosacantha. Finally, the same law as is valid also in the last genus is found in Cenocapsa; here the radial spines have completely disappeared, and the whole skeleton is a simple sphere, but of the same structure, and with the same twenty perspinal pores as in Porocapsa. It is very interesting that this spineless Cenocapsa among the ACANTHARIA exhibits the same shell (a simple hollow sphere) as a last reduced form, which Cenosphæra among the #Sphærellaria# produces as a primitive ancestral form of numerous genera.

{797}The Central Capsule of the Sphærocapsida is spherical, constantly smaller than the enclosing concentric shell, and separated from it by the calymma. Its structure seems to be the same as in the #Acanthonida#, and specially in the Astrolonchida. The pseudopodia (not yet observed) are probably protruded only through the twenty perspinal holes or the eighty aspinal pores.

Synopsis of the Genera of Sphærocapsida.

------------------------------------------------------------------------- I. Subfamily Astrocapsida. Radial spines connected with the porous shell, as long or longer than its radius. Eighty aspinal pores. ------------------------------------------------------------------------- Spines as long as the radius, without external prolongation, 344. Sphærocapsa.

Spines longer than the radius, with external prolongation, 345. Astrocapsa. ------------------------------------------------------------------------- II. Subfamily Porocapsida. Radial spines not connected with the porous shell, shorter than its radius. Twenty perspinal pores. ------------------------------------------------------------------------- Perspinal holes of the shell simple, without external prolongation, 346. Porocapsa.

Perspinal holes of the shell prolonged into radial centrifugal tubuli, 347. Cannocapsa. ------------------------------------------------------------------------- III. Subfamily Cenocapsida. Radial spines disappeared. ------------------------------------------------------------------------- Twenty perspinal holes of the shell simple, without tubular prolongation, 348. Cenocapsa.

Subfamily 1. ASTROCAPSIDA, Haeckel.

Definition.--Radial spines connected with the porous shell, as long as or longer than its radius. Therefore the shell pierced by eighty aspinal pores (four around each spine).

Genus 344. Sphærocapsa,[384] Haeckel, 1881, Prodromus, p. 469.

Definition.--#Sphærocapsida# with twenty radial spines as long as the radius of the shell, without external prolongation; therefore their distal ends inserted in the perspinal holes, each of which is composed of four aspinal pores.

The genus Sphærocapsa is the most common form of the Sphærocapsida, and comprises those species in which the radial spines are as long as the radius of the shell, and therefore are connected with the margin of its aspinal holes, but not prolonged beyond its surface.

{798}1. Sphærocapsa cruciata, n. sp. (Pl. 135, figs. 6, 7).

Aspinal holes nearly circular, with flat radially striated margin. Four aspinal pores of each hole rounded equilateral triangular. Porules of the shell simple, without ring and dimple. Four edges of the spines smooth.

Dimensions.--Diameter of the shell 0.4 to 0.5, of the central capsule 0.3 to 0.4.

Habitat.--North Atlantic, Færöe Channel (Gulf Stream), 1880, John Murray, surface.

2. Sphærocapsa dentata, n. sp. (Pl. 135, fig. 9).

Aspinal holes four-lobed, with broad concave margin denticulated on the periphery. Four aspinal pores of each hole pear-shaped, oblong, elevated in the centre. Porules of the shell simple, without ring and dimple. Four edges of the spines denticulate.

Dimensions.--Diameter of the shell 0.3 to 0.4, of the central capsule 0.2 to 0.3.

Habitat.--South Atlantic, Station 332, depth 2200 fathoms.

3. Sphærocapsa quadrata, n. sp. (Pl. 135, fig. 8).

Aspinal holes square, with concave umbilicus in the centre, surrounded by a convex denticulated margin. Four aspinal pores of each hole nearly square. Shell-porules with a polygonal elevated smooth ring, in the bottom of a shallow dimple. Four edges of the spines smooth.

Dimensions.--Diameter of the shell 0.22, of the central capsule 0.17.

Habitat.--Indian Ocean, south of Australia, Station 159, surface.

4. Sphærocapsa pavimentata, n. sp. (Pl. 135, fig. 10).

Aspinal holes four-lobed, with broad concave, irregularly crenated and figured margin. Four aspinal pores of each hole violin-shaped. Porules of the shell surrounded by an irregularly oblong ring with thick elevated, elegantly crenated margin. Four edges of the spines smooth.

Dimensions.--Diameter of the shell 0.36, of the central capsule 0.3.

Habitat.--South-east Pacific (off Valparaiso), Station 298, surface.

Genus 345. Astrocapsa,[385] n. gen.

Definition.--#Sphærocapsida# with twenty radial spines longer than the radius of the shell, piercing its perspinal holes, with free external prolongation; therefore with four aspinal pores around each spine.

The genus Astrocapsa differs from the preceding Sphærocapsa in the external prolongation of the radial spines piercing the perspinal holes; it assumes therefore the common shape of the Dorataspida more than the other Sphærocapsida do.

{799}1. Astrocapsa tritonis, n. sp.

Aspinal holes circular, with smooth convex margin and four circular aspinal pores. Porules of the shell simple, without ring and dimple. Four edges of the spines smooth, their outer free part about as long as the diameter of the shell.

Dimensions.--Diameter of the shell 0.25; outer length of the spines 0.3.

Habitat.--North Atlantic, Færöe Channel, Gulf Stream (expedition of H.M.S "Triton," August, 1882), John Murray, surface.

2. Astrocapsa stellata, n. sp. (Pl. 133, fig. 10).

Aspinal holes cruciform, with high crenated margin. Four aspinal pores of each hole egg-shaped. Porules of the shell simple, without ring and dimple. Four edges of the spines denticulate; their outer free part twice to three times as long as the diameter of the shell.

Dimensions.--Diameter of the shell 0.36; outer length of the spines 0.5 to 0.8.

Habitat.--Antarctic Ocean (near Kerguelen), Station 152, surface.

3. Astrocapsa quadrifida, n. sp.

Aspinal holes four-lobed, with four prominent teeth between the four roundish aspinal pores. Porules of the shell surrounded by a high polygonal smooth ring. Four edges of the spines denticulate; their outer free part about as long as the radius of the shell.

Dimensions.--Diameter of the shell 0.28; outer length of the spines 0.15.

Habitat.--North Pacific, Station 241, surface.

4. Astrocapsa coronata, n. sp. (Pl. 133, fig. 9).

Aspinal holes circular, with a coronet of numerous thin parallel teeth. Porules of the shell in dimples on irregular polygonal small plates, with coronated ring. Four edges of the spines denticulate; their outer free part about twice as long as the diameter of the shell.

Dimensions.--Diameter of the shell 0.4 to 0.5 ; outer length of the spines 1.0 to 1.2.

Habitat.--North Atlantic, Færöe Channel, Gulf Stream (expedition of the "Knight Errant," 1880), John Murray, surface and at depths varying from 10 to 200 fathoms.

Subfamily 2. POROCAPSIDA, Haeckel.

Definition.--Radial spines not connected with the porous shell, shorter than its radius; therefore the shell pierced by twenty perspinal pores (each one in the ideal radial prolongation of one spine).

{800}Genus 346. Porocapsa,[386] n. gen.

Definition.--#Sphærocapsida# with twenty radial spines shorter than the radius of the shell; therefore their distal ends not connected with the twenty perspinal holes, which are simple, not prolonged into radial tubes.

The genus Porocapsa and the following Cannocapsa form together the small sub-family of Porocapsida, distinguished by the peculiar reduction or retrograde development of the twenty radial spines; all these twenty are present and disposed according to the Müllerian law of the Icosacantha, but they are shorter than the radius of the shell and therefore do not reach it. In the ideal prolongation of the spines the shell is pierced by twenty simple quadrangular or circular perspinal holes.

1. Porocapsa murrayana, n. sp. (Pl. 133, fig. 7).

Perspinal holes cruciform, with smooth thickened margin or with four short teeth between the four lobes. Porules of the shell simple, without ring and dimple. Four edges of the spines smooth. (Differs from Sphærocapsa cruciata, Pl. 135, figs. 6, 7, living in the same locality, mainly in the reduction of the radial spines, which do not reach the shell.)

Dimensions.--Diameter of the shell 0.28; length of the spines 0.2.

Habitat.--North Atlantic, Færöe Channel, Gulf Stream (expedition of H.M.S. "Triton," August 1882), John Murray, surface and in depths from 40 to 640 fathoms.

2. Porocapsa tetrodon, n. sp.

Perspinal holes cruciform, with four triangular prominent teeth between the four lobes of the cross. Porules of the shell with an elevated polygonal ring, in the bottom of a dimple. Four edges of the spines elegantly denticulate.

Dimensions.--Diameter of the shell 0.36; length of the spines 0.12.

Habitat.--North Pacific, Station 253, surface.

3. Porocapsa octodon, n. sp.

Perspinal holes square, with four larger prominent teeth on the sides of the square, and four smaller teeth on its corners. Porules of the shell surrounded by an elevated ring with elegantly crenated irregular margin. Four edges of the spines smooth.

Dimensions.--Diameter of the shell 0.48; length of the spines 0.18.

Habitat.--Arctic Ocean (Greenland), in the contents of the stomach of the Peromedusa, Periphylla hyacinthina.

{801}4. Porocapsa coronodon, n. sp.

Perspinal holes circular, with ciliated margin, which forms a crown of sixteen to twenty-four thin parallel teeth. Poruli of the shell surrounded by an elevated ring with high crenated margin. Four edges of the spines denticulate.

Dimensions.--Diameter of the shell 0.55; length of the spines 0.15.

Habitat.--Antarctic Ocean, Station 154, surface.

Genus 347. Cannocapsa,[387] n. gen.

Definition.--#Sphærocapsida# with twenty radial spines shorter than the radius of the shell; therefore their distal ends not connected with the twenty perspinal holes, which are prolonged outside into radial tubes (each one in the radial ideal prolongation of one inner spine).

The genus Cannocapsa, exhibits the same peculiar reduction of the radial spines as the foregoing Porocapsa; the spines are also here shorter than the shell-radius and do not therefore reach the perspinal holes of the shell. But whilst these latter are simple in Porocapsa, they are prolonged into radial tubules in Cannocapsa; the outer surface bears therefore twenty such cylindrical tubules, separated by a short distance from the inner enclosed spines, but disposed quite regularly according to the law of Icosacantha.

1. Cannocapsa osculata, n. sp.

Perspinal holes prolonged into short cylindrical tubuli, the length of which about equals their diameter. Both ends of the tubuli with smooth thickened margin. Poruli of the shell simple, without ring and dimple. Four edges of the spines smooth; their length equals about four-fifths of the shell-radius.

Dimensions.--Diameter of the shell 0.24; length of the spines 0.09, of the tubuli 0.01.

Habitat.--North Atlantic, Færöe Channel (Gulf Stream), surface, John Murray.

2. Cannocapsa stethoscopium, n. sp. (Pl. 133, fig. 8).

Perspinal holes prolonged into cylindrical tubuli, half as long as the shell radius. Both ends of the tubuli with smooth thin trumpet-shaped margins. Poruli of the shell simple, without ring and dimple. Four edges of the spines smooth; their length about equals three-fourths of the shell-radius.

Dimensions.--Diameter of the shell 0.2; length of the spines 0.08, of the tubuli 0.05.

Habitat.--South Atlantic (west of Tristan da Cunha), Station 333, surface.

3. Cannocapsa tubulosa, n. sp.

Perspinal holes prolonged into cylindrical tubuli, which are as long as or longer then the shell-radius. Both ends of the tubuli with smooth thickened margin. Poruli of the shell simple, {802}without ring and dimple. Four edges of the spines smooth; their length scarcely equals half the shell-radius.

Dimensions.--Diameter of the shell 0.15; length of the spines 0.03, of the tubuli 0.08.

Habitat.--South Atlantic (east coast of Patagonia), Station 318, surface.

Subfamily 3. CENOCAPSIDA, Haeckel.

Definition.--Radial spines completely reduced and absent; shell cavity therefore simple; shell pierced by twenty perspinal pores (each placed in the direction of one radial spine which has disappeared).

Genus 348. Cenocapsa,[388] n. gen.

Definition.--#Sphærocapsida# without radial spines, with simple cavity of the spherical shell, which is pierced by twenty perspinal holes (each one placed in the radial direction of one spine which has disappeared).

The genus Cenocapsa comprises only a single species, but is very remarkable in that it is the most reduced form among all Sphærocapsida. The twenty radial spines of the Icosacantha have perfectly disappeared by complete retrograde metamorphosis, and the only evidence of their former existence (in the ancestral genus Porocapsa) are the twenty perspinal holes remaining in the shell. Cenocapsa is the only form of ACANTHARIA which possesses no radial spines.

1. Cenocapsa nirvana, n. sp. (133, fig. 11, 11_a_, 11_c_).

Perspinal holes four-lobed, cruciform, with four short triangular teeth between the four lobes of the cross. Poruli of the shell in the bottom of an elliptical dimple surrounded by an elevated ring.

Dimensions.--Diameter of the shell 0.2 to 0.3, of the aspinal holes 0.02.

Habitat.--North Pacific, Station 248, surface.

Family XL. #DORATASPIDA#, Haeckel (Pls. 134-138).

Dorataspida, Haeckel, 1862, Monogr. d. Radiol., p. 412.

Definition.--ACANTHARIA with simple spherical lattice-shell, composed of the branched apophyses of twenty equal radial spines meeting in its centre and disposed according to the Müllerian law of Icosacantha. Central capsule spherical, enclosed in the fenestrated shell.

The family #Dorataspida# is the most important family of the #Acanthophracta#, or of those ACANTHARIA in which the radial spines are connected by a complete extracapsular lattice-shell. The Dorataspida represent probably the ancestral {803}stock of this whole order, with the exception of the Sphærocapsida. The four following families of the order may be easily derived from the Dorataspida. The number of genera (seventeen) and of species (one hundred and eight) is in this family greater than in the other five families together. When I constituted that family in my Monograph 1862, it comprised only one genus, Dorataspis, with seven species. The nearly allied genus Haliommatidium (Phatnaspis) belongs to the Belonaspida.

The Dorataspida differ from the other #Acanthophracta# in the simple spherical lattice-shell, which is composed of the meeting apophyses of the twenty radial spines. In three other families of the suborder the shell is not spherical, but ellipsoidal (Belonaspida), discoidal (Hexalaspida), or diploconical (Diploconida). In the Phractopeltida the spherical shell is double, composed of two concentric lattice-spheres. In the Sphærocapsida the simple spherical shell is not composed of the apophyses of the spines, but of innumerable small plates.

The family Dorataspida may be divided into two very different subfamilies, which are probably derived, independently of one another, from two different subfamilies of the Astrolonchida. The first subfamily, Diporaspida, exhibits on each radial spine two opposite apophyses, like its ancestral group, the Phractacanthida (p. 753); whereas the second subfamily, Tessaraspida, possesses on each radial spine four crossed apophyses (opposite in pairs), like its ancestral group, the Stauracanthida (p. 758). Therefore the composition of the spherical shell, produced by the meeting branches of the tangential apophyses, is essentially different in the two subfamilies: in the Diporaspida each radial spine is surrounded by two opposite primary aspinal meshes, in the Tessaraspida by four crossed primary aspinal meshes.

Another principle of division may be established for the whole family by the different mode of composition of the shell, and regarding this important difference we may distinguish also two different subfamilies as #Cladophracta# and #Peltophracta#. In the first and simpler subfamily, the #Cladophracta#, the shell is composed totally (or sometimes partially) of the meeting branches of the apophyses of the neighbouring spines; but in each single spine (or in the most part of them) the branches of the apophyses are not united, and form no lattice-plate (Pl. 137, figs. 1 to 8). Whereas in the #Peltophracta# the shell is composed constantly of twenty perforated plates, as in each single spine the branches of its apophyses are united and form a fenestrated shield with two or four (and sometimes numerous) pores (Pls. 135, 136, 138).

In the Diporaspida as well as in the Tessaraspida we find numerous representatives of the two groups of the #Cladophracta# and of the #Peltophracta#; therefore the whole family of Dorataspida may be divided into four different tribes. The Diporaspida (with two opposite apophyses on each spine) are partly #Cladophracta# (the Phractaspida, Pl. 137, figs. 1-4), partly #Peltophracta# (the Ceriaspida, Pl. 138). On the other hand the Tessaraspida (with four crossed apophyses on each {804}spine) are also partly #Cladophracta# (the Stauraspida, Pl. 137, figs. 5-8), partly #Peltophracta# (the Lychnaspida, Pls. 135-136). The differences and relations of these tribes are placed synoptically in the following table:--

------------------------+------------------------+----------------------- | A. Diporaspida. | B. Tessaraspida. Synopsis of the four |Two opposite apophyses |Four crossed apophyses tribes of Dorataspida.| on each radial spine. | on each radial spine. | Two primary aspinal | Four primary spinal | meshes. | meshes. ------------------------+------------------------+----------------------- a. Cladophracta |1. Tribe Phractaspida. |3. Tribe Stauraspida. All twenty spines (or a | | part of them) without | | lattice-plates. | | | | b. Peltophracta |2. Tribe Ceriaspida. |4. Tribe Lychnaspida. All twenty spines with | | lattice-plates. | | ------------------------+------------------------+-----------------------

All Dorataspida are true Icosacantha, and the twenty spines, composing the spherical shell, are equally developed, regularly disposed according to the Müllerian law, and of equal size; also the distance of their plates from the common centre is equal. Nevertheless they are never of perfectly the same form; in consequence of their peculiar disposition in five zones (each with four spines) certain slight differences are effected, so that with accurate knowledge of the peculiar shell-composition it is generally not difficult to distinguish the spines of the equatorial, the two tropical, and the two polar zones.

Already the central bases, by which the twenty spines are united in the centre of the sphere, exhibit certain differences in the five zones. Commonly these bases are small pyramids, all meeting with their apex in the centre, and the triangular faces of the neighbouring pyramids are supported one upon another. The four equatorial pyramids are commonly six-sided, the other sixteen five-sided; but sometimes there are eight six-sided and twelve five-sided basal pyramids; two opposite polar spines on each pole having a six-sided base (like the four equatorial), the other two polar spines on each pole having a five-sided base (like the eight tropical). Rarely the central bases are perfectly grown together, forming a single spherical central piece of acanthin.

The three different fundamental forms of radial spines, which are found in all ACANTHARIA, the cylindrical, the two-edged, and the four-edged (spines with circular, with elliptical, and with square transverse section respectively) occur also in the different groups of Dorataspida; but commonly the two-edged or compressed form is prevalent in the Diporaspida, the four-edged or quadrangular form in the Tessaraspida. In the majority of species the spines are thickened in the shell-face, where the apophyses arise, and thinner towards the two ends. Usually the outer or distal part of the spine (outside the shell) is longer than the inner or proximal part (inside {805}the shell). The distal apex is commonly simple, conical or pyramidal, rarely bifid or truncate. The edges of the spines are commonly smooth, rarely denticulate or serrate.

The apophyses, or the lateral transverse processes of the radial spines, in the Dorataspida assume the greatest variety and complexity in form, size, mode of ramification, and in composition of the shell. An expert and practised observer may determine easily the range of each spine, whether it be an equatorial (c), or a tropical (b, d), or a polar spine (a, e, Pls. 133-138). The two opposite apophyses of the Diporaspida, as well as the four crossed apophyses of the Tessaraspida, lie constantly in certain meridian planes of the spine, which have a legitimate signification for each of the five zones. The comparative morphology of this regular disposition of the apophyses and the regular meeting of their branches is of the greatest interest, and necessary for the complete understanding of the complicated structure of these wonderful shells.

The pores or meshes of the spherical shell, offering the most varied forms, may generally be divided into two different groups, into sutural and parmal meshes. The sutural pores are bordered by the meeting branches of the apophyses of two, three, or four neighbouring spines, and therefore also by the sutures in which they meet. The parmal pores on the other hand are bordered only by the united branches of the apophyses of a single spine and pierce the shield or lattice-plate formed by them. Therefore the shell-meshes of the #Cladophracta# are all sutural pores (Pl. 137, figs. 1-8; rarely and only in a part of the spines parmal pores also: Zonaspis, Dodecaspis); whereas the shell-meshes of the #Peltophracta#, piercing the shields or lattice-plates of all twenty spines, are always partly sutural, partly parmal pores (Pls. 135, 136, 138). The parmal pores again may be divided into two different groups--aspinal and coronal pores. Aspinal pores ("ad spinam") are those which lie immediately on the sides of the radial spine and are bordered by the primary branches of its apophyses; therefore constantly only two in the Diporaspida, four in the Tessaraspida. Coronal pores on the contrary are those which lie in the periphery of the lattice-plates, surrounding in a circle or crown the aspinal pores and not touching the spine itself. In Dorataspis, Ceriaspis, Tessaraspis, Lychnaspis, &c., all parmal meshes are only aspinal pores (Pl. 135, figs. 2-5; Pl. 136); whilst in Coscinaspis, Acontaspis, Icosaspis, Hylaspis, &c., one part of the parmal pores is aspinal, one part coronal (Pl. 136). The number, form, and size of the coronal pores is very variable and often very large (sometimes more than a hundred in one plate).

The #Cladophracta# exhibit a comparatively simple shell-formation; either all twenty spines or at least a part of them not forming lattice-plates. The most primitive form among these is Phractaspis (Pl. 137, figs. 1, 2). The forty apophyses of its twenty spines are simply forked, and their eighty fork-branches united by forty sutures, enclosing twenty-two sutural meshes: two square polar meshes (between the four polar spines on the poles of the spineless axis, a a a a and e e e e); eight triangular {806}circumpolar meshes (each between two polar and one tropical spine, a b a and e d e); eight quadrangular tropical meshes (each between one polar, one equatorial, and two tropical spines, a b c b and e d c d); and four rhomboidal equatorial meshes (between two tropical and two equatorial spines, c b c d). If the fork-branches be again forked (Phractaspidium, Pl. 137, fig. 3), the number of the sutures and sutural meshes is doubled, and the same is the case in Stauraspis, the most simple form of the Tessaraspida.

A peculiar small group, and an interesting transition for the #Cladophracta# to the #Peltophracta#, is presented by the Zonaspida among the Tessaraspida (Zonaspis and Dodecaspis). Here only one part of the radial spines bears lattice-plates, the other part not. In Zonaspis the four equatorial spines bear lattice-plates, the sixteen other only free branches of the apophyses. In Dodecaspis twelve spines are provided with lattice-plates (four equatorial and eight polar spines), whilst the eight other (tropical) spines are devoid of them.

The #Peltophracta# exhibit a great variety in the form and composition of their twenty lattice-plates or fenestrated shields. In the most simple case (a part of Dorataspis and Diporaspis) the shell is composed of four (equatorial) hexagonal plates, and sixteen pentagonal plates (four tropical and four polar); in this case the four polar plates meet on each pole in one common point. More commonly, however, the shell seems to be composed of eight hexagonal plates (four equatorial and the four polar spines of the hydrotomical plane) and twelve pentagonal plates (eight tropical and the four polar spines of the geotomical plane); in this case only two (hexagonal) polar plates meet on each pole in a suture which separates the two other (pentagonal) polar plates (Pl. 138, fig. 4). In the majority of the Dorataspida the composition of the shell is much more complicated and often very difficult to understand. Often the surface of the plates is covered with a network of elevated crests, by which concave blind dimples are separated (Ceriaspis, Hystrichaspis, Pl. 138); and sometimes these dimples become pierced by coronal pores (Pl. 138, fig. 11, &c.).

Peculiar by-spines or "accessory spines" cover the outer surface of the shell in a great part of Dorataspida, and commonly these most characteristic by-spines are not placed radially, but parallel to the radial spine, from the lattice-plate of which they arise (Pl. 135, figs. 1, 5; Pl. 137, figs. 4-8; Monogr. d. Radiol., 1862, Taf. xxi. figs. 8, 9). They are commonly placed perpendicular to the sutural condyles, or the branch-ends of the apophyses; so that close to each suture arises a pair of divergent by-spines, belonging to the meeting apophyses of the two neighbouring spines, which meet in the suture (Pl. 137, fig. 4). Rarely these thin, bristle-shaped by-spines are quite simple and straight, commonly they undulate or are zigzag and often armed with recurved hooks. Sometimes they are also forked or arborescent (Pl. 138, fig. 7).

The Central Capsule of the Dorataspida is constantly spherical and about one-third smaller than the enclosing shell, from which it is separated by the spherical calymma. {807}The membrane of the central capsule is commonly rather thin, and pierced by the twenty radial spines, meeting in the centre of the capsule. Between these lie innumerable small pores for the radiating pseudopodia; however, in many cases (and perhaps constantly) these pores exhibit a certain regular disposition. In many species the central capsule encloses Xanthellæ or symbiotic yellow unicellular Algæ. The nucleus becomes cleft very early in the majority of Dorataspida.

Synopsis of the Genera of Dorataspida.

------------------------------------------------------------------------- I. Subfamily Diporaspida. Each radial spine with two opposite primary apophyses; therefore the whole shell with forty primary apophyses. -------------------- I. Tribe Phractaspida. Twenty radial spines without lattice-plates; no normal pores. ------------------------------------------------------------------------- No by-spines, 349. Phractaspis.

With by-spines, 350. Pleuraspis. ------------------------------------------------------------------------- II. Tribe Ceriaspida. Twenty radial spines all with lattice-plates produced by union of the branched apophyses of each plate. ------------------------------------------------------------------------- { { No by-spines, 351. Dorataspis. { Plates not { Forty parmal { dimpled, { With by-spines, 352. Diporaspis. pores (two { without { in each { network { No by-spines, but plate)--no { of crests. { free apophyses, 353. Orophaspis. coronal { pores in { Plates dimpled, } No by-spines, 354. Ceriaspis. the plates. { with a network } { of crests. } With by-spines, 355. Hystrichaspis.

Eighty to two hundred or more } No by-spines, 356. Coscinaspis. (in each plate two aspinal } and two to ten or more } With by-spines, 357. Acontaspis. coronal pores). } ------------------------------------------------------------------------- II. Subfamily Tessaraspida. Each radial spine with four crossed primary apophyses; therefore the whole shell with eighty primary apophyses. -------------------- III. Tribe Stauraspida. Twenty radial spines all or partly without lattice-plates. ------------------------------------------------------------------------- { No by-spines, 358. Stauraspis. All twenty spines without { lattice-plates. { With by-spines, 359. Echinaspis.

Four plates with, sixteen } without, lattice-plates. } With by-spines, 360. Zonaspis.

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