Salt-range fossils

Front matter

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Introduction

In the Introduction to Vol. I of the present work it was proposed to devote a proper volume to the description of the fossil contents of the Ceratite heds.

Even then it was highly prohahle that the Ceratite beds were representative, in part or entirely, of the Trias of Europe, and this probability has been greatly strengthened by the publications on triassic strata in general that have appeared in the meantime. Still, however, it is not possible to say with certainty what parts of the Trias may be represented by the Ceratite formation of the Salt- Range. A discussion of this question will only be possible after the fossils shall have been described in detail.

Mr. Wynne was the first who separated this rock group from the underlying palaeozoic series with which it had been united by Fleming and Theobald.

According to Mr. Wynne's indications the group forms indeed stratigraphically a member of the palaeozoic series ; and it is not on geological, but solely on palaeontological grounds that it can be separated from the Productus-limestone group. As far as my own observations go, the stratigraphical conformity of the Ceratite beds with the next lower members of the palaeozoic rock groups is everywhere obvious. Only on a very close examination one finds, off and on, a section which gives some indications that rather considerable physical changes in the conditions of the deposition of rocks must have taken place between the formation of the topmost beds of the Productus-limestone and the strata belonging to the Ceratite formation. At most places some unfossiliferous beds intervene, and sometimes even conglomerates are deposited at the base of the Ceratite group, which show that a certain amount of denudation must have taken place at the commencement of these latter beds.

As a natural consequence of the views held by Messrs. Theobald and Fleming, the fossils collected by them out of these beds were described as palaeozoic species by Mons. de Koninck, while there was an intermixture of these with the truly palseozoic contents of the Productus-limestone. These fossils were described by Mons. de Koninck in the Quarterly Journal of the Geological Society of London for the year 1863, Vol. XIX.

There are chiefly only Cephalopoda which came out of the Oeratite formation ; and for about ten of the species described by de Koninck there can be hardly any question as to their original geological position. There is chiefly only one species about which grave doubts exist, and this is Sageceras (Ceratites) hauerianus, Koninck, which has been mentioned by me already, Vol. I, p. 39. As no new specimen of this species has been found by me, and the original seems apparently to be lost, the question cannot be settled definitively at present. I shall not mention the species again in the text, though it is by no means denied that it may form part of the fauna of the Ceratite formation.

The remainder of the species described by de Koninck can be recognised without great difficulty and will be redescribed later on in the text.

As regards the subdivisions that can be made out within the Ceratite formation, we can distinguish two different orders.

There are, before all, three large subdivisions, which, on the whole, are very conspicuous and might, for a part at least, be recognised even by the casual observer. Below, there is a group of beds in which smooth Ceratites are by far predominating and in which other fossils are of comparatively rare occurrence. This group is generally of considerable thickness and of varying petrographical description.

Above this follows another group, characterised by richly ornamented forms of Ceratites, occurring in great numbers. At the side of these, countless bivalves are to be found, accumulated mostly in proper beds and forming distinctly bivalve limestones. In most cases, however, the shells are so firmly imbedded in the rock that it is impossible to detach them in a fit state for description.

The uppermost division of the Ceratite formation is made up for the greater part of massive dolomites, sometimes cavernous, and then rarely containing fossils, associated with some sandstones and some limestones, also with countless bivalves, on the top. Fossils are everywhere rare in this division, except in the topmost limestones, which, however, only very rarely allow of the fossils being detached. Thus, I shall have to describe only very few things out of this division. As regards the thickness of this group it is the thickest of all in the Tredian hills, amounting apparently locally up to several hundred feet. At other places its thickness is again much less considerable.

On the whole, we may say that the middle division is the least conspicuous one never attaining a great thickness and very rarely comprising a great variety of rock, but mostly composed purely of limestones of rather insignificant thickness.

The three divisions can easily be subdivided further; but, before entering on

INTRODUCTION. 3

these details, it will perhaps be well to distinguish each of the divisions by a proper name.

The first of the divisions, which is the most conspicuous and has at the same time the greatest lateral extension, may best bear the name of Ceratite beds properly speaking. It comprises those strata which have furnished the greatest part of the species of Ceratites that have been described by de Koninck from the Salt-Range ; while also Mr. Wynne had chiefly these beds in view when separating his Ceratite group from the Productus-limestone series.

The second division had not been known and distinguished before I came to the Salt- Range, and the fauna contained in these beds is an entirely new one. In order not to prejudice anything with regard to a possible parallelisation of these beds with some division of the European Trias, I give to it the name of " Bivalve limestones," as I had done already in my note-book, when on the ground.

The third division may be called the " Dolomite group," with reference to its prevailing rock.

a, Ceratite Beds.

This division can be very conveniently subdivided into three groups, each of which contains a rich and characteristic fauna.

The lowest of these groups is composed of thinly-bedded very hard limestones of not very considerable thickness. I shall quote this group as " Lower Ceratite limestones!^

Above these follow greenish-grey marls with many concretions and irregular beds of marl stone. Thin limestone beds, having a cone-in-cone structure, are also of frequent occurrence. I shall call these beds " Ceratite marls,"

The next higher strata are composed mostly of yellow soft sandstones, which sometimes, however, also become calcareous, and then are of a more greyish colour. I shall introduce for these the name of " Ceratite sandstones."

Within the group some subdivisions may yet be distinguished : the lower sandstones, the Stachella (or BelleropJion) beds, and on the top the beds with Flemingites (Ceratites) flemingi.

With these latter deposits the Ceratite beds, properly speaking, come to a close.

6. Bivalve Limestones

Within this large group of rocks two subdivisions can be very conveniently distinguished.

The lower half of this group is mostly composed of very hard limestones, with intercalated marls of grey colour. Sometimes, but rarely, the limestones become yellow, and are then a little sandy. They are mostly crowded with richly sculptured ceratitoid cephalopoda, whilst the bivalves are of rarer occurrence.

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4 SALT-EANGE IPOSSILS.

Therefore I propose to designate these beds by the name of " Upper ceratite Umestonesy

The upper half of the Bivalve Limestone group is composed of yet harder limestones, which ring loudly under the hammer, but which have no such even bedding planes as is the case with the " Lower ceratite limestones." These beds are crowded with the remains of bivalves, whilst cephalopoda are of rather rare occurrence. At most localities it is impossible to extract the fossils out of this rock and only at some places, where the rock becomes somewhat softer, marly or sandy, has it furnished a number of specimens in a fit state for description.

The designation that ought to be given to this subdivision might perhaps best simply be styled " Bivalve beds."

It is not possible to distinguish any further subdivision within this group, as its vertical extension is very limited and the rocks very uniform in character,

c. Dolomite Group.

The prevailing rock of this group is a compact dolomite of a somewhat yellowish colour. In this rock fossils have not been found up to the present. At some very rare localities these dolomites become softer and somewhat brecciated and cavernous. At the same time this changes the colour into grey or reddish. In this variety of rock I detected some few internal castes of bivalves and gasteropoda. Besides the dolomites there are also some grey sandstones and greenish marls, but I am unable to assign a distinct level to them.

Only on the top of the whole group, just at the base of the variegated marls and sandstones, a bed of limestone can be distinguished, crowded with the remains of indistinct bivalves, and containing a single cephalopod of a quite peculiar shape.

These limestones may be distinguished as a proper subdivision, and can be quoted as " Topmost limestones."

According to all that has been said we arrive at the following classification of the Ceratite formation of the Salt^Range : —

. f Topmost limestonee.

Dolomite Group .i tv i vl- i i ^ I. Dolomitic beds.

Bivalve Limestones ( ^^^^^^^ ^«^^-

(.Upper ceratite limestone,

/ r^iemingUesflemingiheA.a.

I Ceratite sandstone -j Stachella [heUerophon) beds.

Ceratite Beds . j ( Lower sandstone beds.

/ Ceratite mavis. \ Lower ceratite limestone.

Among the fossils contained in all these strata the cephalopoda by far predominate; all the other organic remains occurring are insignificant in comparison with |;his class.

Apaong the species described by Mons, de Konincjf in the Quarterly Journal of

INTRODUCTION. 5

the Geological Society, the following can be considered with tolerable certainty as coming out of the Ceratite formation : —

Acrodus, n.sp.

„ flemingianus, Kon.

Saurichthys indicus, Kon.

Ceratites flemingianus, Kon.

„ murchisonianus, Kon.

„ planulatus, Kon.

„ lyellianus, Kon.

„ latifimbriatus, Kon.

„ huchianus, Kon,

„ davidsonicmus, Kon.

„ lawrencianus, Kon.

Goniatites (?) gangeticus, Kon.

Originally there were described altogether 44 species by Mons. de Koninck

from the Salt- Range. Of these, 27 have been found to come out of the Palaeozoic

series, whilst not more than the above enumerated twelve species are attributable

with certainty to the Ceratite formation, and there remain four more for which

the horizon cannot be indicated with certainty. It is, however, highly probable

that two of them—

Isastrcea araehnoides, Kon.

Nerincea sp.

have been either collected in the variegated series, or have rolled down among the

jnesozoic species from yet higher strata.

One can say nearly with certainty that this has been the case with the two

remaining species —

Nautilus burtini, Galeotti,

Macrocheilus depilis, Kon.

of which the latter appears to be probably the internal cast of some tertiary gasteropod.

The triassic cephalopoda described by Mons. de Koninck have received, with the exception of one, the designation "Ceratites" on account of the ceratitic development of the sutural lines in all the species. Since, however, it has been ■shown that ceratitic lobes are not characteristic of a single genus only, but that they designate a certain state of development within the whole order of Ammonitoidea, and that very different am monoid shells may exhibit at times, in certain rock systems, ceratitic lobes, such a designation cannot longer be accepted for the forms described by him ; and it may be stated already here that only a single ceratite in a restricted sense is among the whole lot of de Koninck's species.

The same is the case with Goniatites gangeticus^ which is also a species that /cannot remain lo»^er under that heading.

A difficulty that arises in trying to identify de Koninck'^ figures with the natural specimens collected in the Salt- Range consists in the circumstance that he has evidently not taken the drawings of the sutural lines from the same specimens that are represented in the full figures : thus, a certain confusion is unavoidable, and it is to be regretted that some most eminent palaeontologists have, at times, been led astray by this circumstance, which is most striking in Qon. gangeticm and

Ceratites flemingianus.

An author that has made many most excellent remarks about the species described by Mons. de Koninck from the Salt-Range is Dr. v. Mojsisovics ; and I shall barely be able to write a page of the following descriptions without recurring again and again to Mojsisovics' works.

With regard to the Salt- Range Cephalopoda especially, he attributed in his large

work on the Mediterranean triassic province the following species to the genus

Meekoceras : —

MeeTcoceras planulatum, Kon., sp.

„ davidsonianum „ „

J, buchianum „ „

whilst in his " Arctic Triassic Fauna " he transferred yet another species to the same genus : —

Meekoceras lawrenoianwm, Kon., sp.

Also, in his " Mediterranean Triassic Province " he considered Goniatites gangetious, Kon., as probably belonging to his genus Lecanites.

Besides this distinct mention of certain species as belonging to other genera, we find also some passages in Mojsisovics' works, in which he speaks of the genera Meekoceras and Xenodiscus being diversedly represented in the triassic beds of the Salt-Range.

In this manner several forms occurring in the Salt-Range have already been determined definitively : as, however, Mons. de Koninck's figures are not quite absolutely reliable, there may, occasionally, still remain some doubt as to the systematic position of some of his species.

A most striking instance in this respect is exhibited by deKoninck's Ceratites flemingianus, in which the drawing of the sutural lines is absolutely fantastic, as will easily be detected in comparing my figures of the genus i?'^emiw^*<es with de Koninck's drawing.

And just this phantastic drawing has apparently induced Prof. Karpinsky to take notice of the mentioned species. In the " Melanges G^ologiques et Pal^ontologiques tires du Bulletin de TAcaddmie Imperial de St. Petersbourg," Vol. I, p. 79, he represents Ceratites flemingianus as the descendant of the genus Oastrioceras, which itself again is brought into connection with GlyUoceras, Hyatt. He thinlf s that deKoninck's species is similar in all respects to Gastrioceras with the sole exception of the large laterallobus, which is denticulated, whilst the same part is entire m Gastrioceras. My drawings, however, show that not only the first, but also the

INTRODUCTION. 7

second and third lobes (auxiliary lobes) are strongly denticulated. The affinity, therefore, of Cerat. fiemingianus with Oastrioceras appears to be strongly questionable.

In the Records, Geological Survey of India, Vol. XIII, 1880, p. 94, Griesbach has published a paper, under the title : " Palseontological Notes on the lower Trias of the Himalaya," in which he also takes notice of some species of cephalopoda occurring in the Salt-Range. I shall leave it to the discussion of the geological results obtained from the description of the Triassic fossils to enter into detailed appreciation of the palseontological zones which the author introduced in this paper within the triassic beds of the Salt-Range. In this place I shall only note down the different determinations of species occurring in the Salt-Range, as followed out by Mr. Griesbach. He mentions : —

PtycJiites lawrencianus, Kon., sp.

Norites planulatus, Kon., sp.

Ophiceras lyellianum, Kon., sp.

Xenodiscus gangeticus, Kon., sp. „ demissus, 0pp., sp.

I cannot enter now on the value of these determinations ; they will be discussed in detail in the description of the respective species.

Last, not least, there mUst be mentioned Geheimrath Beyrich's classical work on the Cephalopoda of the Muschelkalk of the Alps. In this paper many remarks on Indian triassic Cephalopoda are contained, and chiefly the Himalayan species are discussed in detail. Also the Salt-Range forms are repeatedly mentioned, and I shall have occasion to refer in the proper place to those excellent remarks.

This is all that has come to my notice with regard to species from the triassic beds of the Salt- Range having been mentioned by later writers, and I can now proceed to give the specific descriptions.

VERTEBRATA.

Class: PISCES.

There are but few remains of fishes among the materials collected by myself and others in the Ceratite beds of the Salt-Range.

Already Mons. de Koninck had received some fish teeth from Dr. Fleming for description, and some of these specimens are contained in the collections of the Geological Society of London. It is not possible for me to give more accurate indications with regard to these things than those that have already been drawn up by Mons. de Koninck, as now-a-days no exact determinations of such teeth can be executed, except by microscopical sections, which of course cannot be prepared when only a single specimen of each species is available.

I therefore content myself with regard to Mons. de Koninck's species by reproducing his descriptions. The material collected by myself is very scanty, and barely sufficient to determine the genera with absolute certainty.

I must express here my most sincere thanks to Prof. Dames and Dr. Jaeckel, of Berlin, for their kind collaboration in trying to determine these few fish-remains ; and chiefly Dr. Jaeckel has taken great pains to arrive at a safe determination of a little tooth of Acrodus, for which I shall introduce the name of Acrodus jaeckelL

Sob-elass : TELEOSTEI.

Order: PHYSOSTOMI.

Family: HOLOPL'EVBID^.

Genus: SAURIOHTHYS, Ag.

It is on the authority of de Koninck that I quote this genus as occurring in the Salt-Range. The characters of the specimens attributed by de Koninck to this genus are, however, not quite in accordance with what one is generally wont to attribute to Saurichthys, as the transversal section of the teeth of that genus is generally not compressed, but more or less circular. In other respects, on the contrary, the two teeth remind us strongly of Saurichthys ; and as the determination of these things can hardly be definitively settled without having microscopical sections prepared, I accept his determination in a provisional way, until more extensive materials shall have been collected in the Salt-Range.

No other specimens have, up to the present, been detected belonging to the genus but the two that were at the disposal of Mons. de Koninck : —

1. Satjeichthts ? iNDicus, Koninck : PI. I, fig. 3 (enlarged two times), fig. 4

(enlarged six times).

1863. Semriehihys indicus, Kon. : Quart. Journ. Geol. Soc. Lond. Vol. XIX, gt 17, pi. VIII, figs. 6, 2. 1863. Saurichthys indicus, Kon. : Fossiles PaMoz. de I'lnde , p. 4, pi. VIII, figs. 6, 7.

Mons. de Koninck characterises his species in the following manner : —

" The teeth which I have attributed with some doubt to the genus Saurichthys, established by Mons, Agassiz, on account of their compressed form, are very small, very shining and of a brownish colour. Of the two specimens which have served for description, the one is 2, the other 6 millimetres in length. The latter is strongly striated at its base and resembles Saur. MougeoU, Ag. It is somewhat less compressed than the other, whose surface is entirely smooth, Both specimens have a strongly pointed apex and cutting edges on both sides. The transversal section is sub-oval.' '

I have nothing to add to this very accurate description, which, after a close inspection of the specimens contained in the Geological Society*s collection, appears ta be perfectly correct.

Locality and Geological Position. — The two specimens of this species were collected by Dr. Fleming at Varcha from a grey limestone.

It is impossible to say from what part of the Ceratite formation they may have come. On the other hand, it appears highly probable that they belong to the triassic fauna, and not to that of the Productus-limestoUe, though from the compositioa of the rock alone it is barely possible to tell, with absolute certainty, whether the one or the ether is the case.

CERATITE POEMATION— PISCES. 9

The specimens are preserved in the collection of the Geological Society of London.

Remarks. — It has been stated ahove that the position of this species in the genus Saurichthys is very doubtful, de Koninck having already pointed out the circumstance. The materials however, which are not at my disposal at this moment, but have been examined by me some years ago, are too limited to give a positive opinion on them.

Sub-class: GANOIDEI.

Order: LEPIDOSTEI.

Eamily: SPE^EOBONTID^.

Genus : COLOBODUS, Ag.

The remains that can be attributed to this genus are extremely fragmentary, and I should not have ventured to decide the point as to the systematic position of these things had not Dr. Jaeckel expressed, independently of myself, the opinion I had formerly, though with great doubts, also entertained, that they belonged to the genus Colobodus.

The remains represent a few scales, some small undeterminable fragments of the skeleton, and a single tooth.

The coarse sculpture of the bone fragments, and the bluntly conical shape of the tooth have induced me to attribute them to Colobodus. It must, however, be understood that the determination can by no means be considered as above every doubt. According to the manner, however, in which the remains that are at my disposal have been found to occur in the Salt-Range, there is much hope that a closer search may reveal even complete specimens.

1. CoLOBODTJS DAMESij Waagen, n. sp., PI. I, fig. 1 a, b, c, e, Is. (The figures «, 6, c, e, k are enlarged from fig. 1.)

All the remains existing of this species are disseminated on a single slab of limestone, intermingled with the remains of Gyrolepis. Not even two of the scales have retained their natural position, but all are strewn irregularly over the whole surface.

There are about six or seven scales which, with some probability, can be attributed to Colobodus. They are of very varying shapes, but mostly badly preserved or fragmentary. Only two of them show beyond every doubt their original shape , and have at the same time their external face distinctly exposed.

These are, like most of the others, of an obliquely rhombic shape, the one (fig. (?) strongly elongate, the other (fig. a) much shorter and broader. Sometimes there is on one side a smooth margin, which has been covered by the following scale. The greatest part of the outer surface of the scales is covered by a dark -brown strongly shining enamel which shows strong diagonal folds, exhibiting irregular slight

c

^Q SALT-RANGE FOSSILS-

lateral bends, wHch are often bifurcating and project very slightly above the marsins of the scales. The coarseness of the sculpture and the high elevation of the folds are very characteristic, and strongly suggestive of the idea that these scales must have belonged to some species of Colobodus.

The same is the case with the small fragmentary skeleton hones which are exposed on the same limestone-slab. The worm-like, coarse, irregular elevations, which are also covered by a shining brown enamel, are in character exactly like the sculpture that is generally observed on parts of the skeleton of Colohodm.

The case is different with regard to the little tooth represented in fig. 1 To. The general shape of this tooth is very little in accordance with what one generally is wont to see determined as teeth of Golohodus, as these are, for the greater part, about hemispherical, with a little wart in the middle. As regards however this latter character, it is stated by Prof. Dames in his excellent treatise on the triassio Gam^ds, that this wart very easily disappears by the usage of the teeth, which then appear nearly smooth. The hemispherical teeth are situated in the mouth of Colobodus on the palatine bones, whilst on the margins of the mandibles, according to Dames* indications and drawings, bluntly conical teeth appear, which are on the whole very rarely observable, but resemble in their outline very much the tooth represented in my figure. Such teeth are to be found drawn on PI. IV of Dames' work, where the dentition of Colobodus maximus, Quenst., is delineated. The Indian tooth is smaller than any of those there represented, and evidently belongs to another species, but in the whole shape it is very similar.

Another circumstance which makes it highly probable that this tooth must be attributed to Colobodus and belongs to the same species, like the scales and fragments of skeleton bones described above, is this, that on this limestone-slab on which all these remains are exposed, only two forms are distinguishable, one Gyrolepis and one Colobodus. That the tooth here under consideration cannot belong to Gyrolepis is rather obvious, whilst, on the other hand, it is very similar to the mandible teeth of Colobodus.

The close juxtaposition of all these remains makes it highly probable that all that can be attributed to the genus Colobodus must belong to one and the same species of this genus.

The tooth measures 2 mm. in length and 1'5 mm. in breadth at the base. It is covered by a shining enamel on the top and appears to be much worn by usage. Of the wart on the top there is nothing visible. The lower part shows a very indistinct kind of vertical striation, which is by no means regular, as it is exhibited by the enlarged figure k on my PI. I. This striation is probably only the result of a slight compression of the substance of the tooth.

Locality and Geological Position. — The limestone-slab on which all these remains are exposed was collected by myself not far from the village of Virgal in the lower ceratite limestone, just at the limit of the Ceratite marls.

B.emarTcs.—T\iB present species is easily distinguishable from all the species of Colobodus described from Europe by the coarse diagonal folding of the scales, which

CERATITB FORMATION— PISCES. 11

folding is mostly transverse in the European species, and by the smaller size of the single tooth that has been found up to the present.

Order: HETEROCERCI.

Family: FAL^ONISCID^.

Genus: GTROLEPIS, Ag.

The remains belonging to this genus are very few, and their attribution to Gyrolepis is by no means certain.

There are some scales and a single tooth which I can attribute to this genus.

As these remains occur on the same slab of limestone on which the remains of Colobodus are exposed, there is some hope that a closeir search on the spot may reveal also better determinable materials of this genus.

1. Gykolepis, sp. indet. PI. I, fig. If, g, Ji, i. (The figures/, g, h, i are

enlarged from fig. 1.)

There are not more than three scales, of which, however, only one shows the external side, which I am inclined to attribute to the genus Gyrolepis. The scale which exhibits the external side is of a rhomboidal shape and covered by rather low diagonal folds, which often bifurcate and are on the whole rather irregular. . The whole surface is covered by a shining brown enamel.

The other two scales, though exhibiting the internal face, are in their outline so very similar to the first one, that it appears highly probable they should belong to the same fish. The marks on fig. h are most probably only products of weathering. The longest diameters of- the scales are 4""°, 6°"" and S'S""" respectively.

Together with these scales there is on the same slab of limestone a little tooth preserved, which is, though very small (its length being not more than 1'75 °"°), very slender and acutely pointed, and presents in this respect a strong contrast to the other tooth exposed on the same slab and which I have attributed to the genus Colobodus.

Its surface is covered by brown shining enamel, which appears to be perfectly

smooth.

In its whole appearance this tooth shows much similarity to the teeth as figured by Prof. Dames in Gyrolepis albertii, Ag. On the whole, it seems, there canno remain much doubt that this tooth also belongs to some species of Gyrolepis. Dr. Jaeckel suggested to me that it perhaps should be attributed to Saurichthys. This is an opinion that on the whole deviates not very far from my own, if one considers that Martin has united the genus Gyrolepis altogether with Saurichthys. On account of the smallness of this tooth I am, however, rather inclined to follow the opinion expressed by Prof. Dames to me, and attribute it to Gyrolepis.

As now the scales and this tooth, which both have been recognised as most probably beloaging to some Gyrolepis have been found in close juxtaposition, there is

c2 a great probability that tbe two belong to one and the same species. The materials are, however, too scanty to give a proper name to these fragmentary parts.

Locality and Geological position. — The materials of this species have been detected n a slab of limestqne, on which also the remains of Golobodus are preserved, which were collected by myself near Virgal in the Lower Ceratite limestone, just at the limit towards the Ceratite marls.

BemarJes. — The present species is readily distinguishable from all the European species of the genus by the broad, flattened folds that are exhibited by the enamel of the scales. In this respect the Indian form seems to indicate a well-distinguishable species, which, however, cannot be exactly circumscribed, owing to the scantiness of the materials at hand.

In Europe the different species of Gyrolepis extend from lower Bunt- Sandstone to the topmost beds of the triassic formation. The geological position of the Indian species is probably very low down in the Bunter.

Sub-class: SELACHII.

Order: SQUALOIDEI.

Eamily: CESTBAQIONTID^.

Genus : ACRODUS, Ag.

This genus has most recently found an excellent ^escriber in Dr. Jaeckel, who has shown that it must be characterised chiefly by the internal microscopical structure of the teeth.

Outwardly the teeth can be recognised by the longitudinal median ridge that extends from one end to the other, by the transverse irregularly bifurcating wrinkles that originate at this ridge and the somewhat oblique position of the roof.