Chapter X…

Chapter X

GEOGRAPHICAL DISTRIBUTION OF LAND AND FRESH-WATER MOLLUSCA--THE PALAEARCTIC, ORIENTAL, AND AUSTRALASIAN REGIONS

The Mollusca afford specially valuable evidence on problems of geographical distribution. This fact is largely due to their extreme susceptibility to any change in the conditions of life. Genera which are accustomed to live in a certain temperature and on certain food, cannot sustain life if the temperature falls or rises beyond certain limits, or if the required food be not forthcoming. There is therefore a marked contrast between the Mollusca of the tropics and of the temperate zones, while different regions in the same latitude, whether within or without the tropics, often show great diversity in their fauna. Every region is thus characterised by its Mollusca. The Mollusca, for instance, of Australia or of South Africa characterise those countries quite as much as do the kangaroo and the emu, the hartebeest and the ostrich; there is nothing like them anywhere else in the world. In the Greater Antilles the Mollusca stand out beyond all other forms of life as characteristic of the islands as a whole, and of each separate island in particular.

The geographical distribution of the land and fresh-water Mollusca must be considered quite apart from that of the marine Mollusca. The sea offers no such serious barriers to the spread of the latter as the land does to the spread of the former. If we were to journey to the Azores, and turn our attention to the land-snails, we should find them almost wholly peculiar, while amongst the sea-shells we should recognise many as occurring also on our southern coasts, and few that were different from those of the Mediterranean. The marine Mollusca of the Sandwich Islands, in spite of the enormous intervening distance, are not very different from those of Natal, but the land Mollusca of the two countries are as widely different as is possible to imagine.

Land Mollusca are, as has been remarked, fettered to the soil. Quadrupeds, birds, fishes, and reptiles are provided with organs of motion which enable them to overpass barriers of various kinds. Even plants, although themselves incapable of motion, may be conveyed in every direction by means of seeds, which are either wafted by the wind or adhere to the skin of animals. But the Mollusca have no such regular means of transport, and are, in a large number of instances, limited to districts of a certain character of soil, or producing certain kinds of vegetation.

The localisation, both of genera and species, occurs all over the world. The genus Achatinella, which is peculiar to the Sandwich Islands, is found there in a profusion of species. It lives in the mountain valleys which radiate from the central ridge of each island, and each valley is characterised by its own peculiar set of species. The great carnivorous Glandina is restricted to Central America and the adjacent parts of the two continents, with one or two species in Southern Europe. Bulimus proper is restricted to South America; Achatina to Africa south of the Sahara; Tornatellina to the Pacific Islands; Cochlostyla to the Philippines; Cylindrella and Bulimulus are peculiar to the New World; Buliminus, Nanina, Scarabus, and Cassidula to the Old.

Extreme cases of this restriction of habitat sometimes occur. Thus Limnaea involuta is found only in a single small mountain tarn in Ireland; Clausilia scalaris along a narrow strip of limestone in Malta; Strophia nana is confined to a few square rods on an island that is itself a mere dot in the Caribbean Sea; the genus Camptonyx occurs only in the neighbourhood of Mt. Girnar, in Gujerat; and Lantzia in moss on the top of a mountain in Bourbon.

Attempts to colonise snails in strange localities have usually resulted in failure, especially when the attempt has involved serious changes of environment. The common Cochlicella acuta of our coasts resists all endeavours to establish it beyond a certain distance from the sea. Snails brought from the Riviera and placed under almost similar conditions of climate on our own southern coasts have lived for a while, but have very rarely taken permanent root. Mr. H. W. Kew[354] has collected a good many of these attempts to acclimatise species, the general success of which seems to depend almost entirely on a restoration of the old conditions of life.

At the same time there are certain species which exhibit a curiously opposite tendency, and which seem capable of flourishing in almost any part of the world, and under the most varied surroundings. Our own common garden snail (Helix aspersa) is a striking instance of this adaptability to new conditions. It has been established, by art or by accident, in Nova Scotia, Maine, South Carolina, New Orleans, California, Mexico city, Cuba, Hayti, Cayenne, Brazil, Valparaiso, Cape Town, the Azores, St. Helena, Mauritius, Loyalty Islands, and Australia. The great Achatina fulica of East Africa has been established first in Mauritius, and from thence has been carried to the Seychelles and Calcutta. Helix lactea, a common Mediterranean species, has been carried to Teneriffe and Montevideo; Helix similaris, whose fatherland is Eastern Asia, has been transported to Mauritius, Bourbon, West Africa, West Indies, Brazil, and Australia; Ennea bicolor (Eastern Asia) to India, Bourbon, Mauritius, West Indies; Stenogyra decollata (Mediterranean basin) to South Carolina; S. Goodallii (West Indies) to British pineries; Helix Hortensis to New Jersey. Seven common English species (Limax gagates, Hyalinia cellaria, H. alliaria, Helix aspersa, H. pulchella, Pupa umbilicata) have become naturalised in St. Helena,[355] and as many as nineteen in Australia.[356]

Cases of artificial transport of this kind are readily detected; they follow the lines of trade. The snails themselves or their ova have been accidentally enclosed with plants or mould, or have adhered to packing-cases, or to hay and grass used in packing. Thus they constitute no disturbance to the general rule of the persistent localisation of species and genera, and there is little fear that the evidence which the geographical distribution of the Mollusca brings to bear upon the general problems of distribution will be confused by any intermixture of fauna naturally distinct.

Land Mollusca: Barriers to Dispersal.--The chief natural barriers to dispersal are extremes of temperature, the sea, mountain ranges, and deserts. Rivers, however large, seem of little effect in checking dispersal. There is no appreciable difference between the land Mollusca north and south of the Ganges, or north and south of the Amazon. Living snails, or their ova, are no doubt transported from one bank to another on floating débris of various kinds. The barrier offered by the sea is obvious, and at first sight appears insurmountable; but the facts with regard to oceanic groups of islands like the Azores and Canaries (see p. 297) show that even a stretch of salt water many hundred miles in breadth may be ineffectual in preventing the dispersal of Mollusca.

Mountain ranges, provided they are too high to be scaled, and too long to be turned in flank, offer a far more effective barrier than the sea. Every thousand feet upward means a fall of so many degrees in the mean temperature, and a change, more or less marked, in the character of the vegetation. There is generally, too, a considerable difference in the nature of the climate on the two sides of a great mountain range, one side being often arid and cold, the other rainy and warm. The combined effect of these influences is, as a rule, decisive against the dispersal of Mollusca. Thus the Helices of California are almost entirely peculiar; one or two intruders from states farther east have succeeded in threading their way through the deep valleys into the Pacific provinces, but not a single genuine Californian species has been able to scale the heights of the Cascade Mountains. The land Mollusca of India are numbered by hundreds; not one penetrates north of the Himalayas. According to Mr. Nevill,[357] the change from the Indo-Malayan to the so-called European molluscan fauna at the northern watershed of the Kashmir valley is most abrupt and distinct; in two days’ march northward, every species is different. Ranges of inferior altitude, such as the Pyrenees, the Carpathians, or the Alleghanies, may be turned in flank as well as scaled, and we find no such marked contrast between the Mollusca on their opposite sides.

The most effective barrier of all, however, is a desert. Its scorching heat, combined with the absence of water and of vegetable life, check dispersal as nothing else can. The distribution of the Mollusca of the Palaearctic Region is an excellent instance of this. Their southern limit is the great desert which stretches, with scarcely a break, from the west coast of Africa to the extreme east coast of Asia. The Mediterranean offers no effectual barrier; shells of southern Europe are found in profusion in Morocco, Tunis, and Egypt, while all through Siberia to the extreme of Kamschatka the same types, and even the same species, of Mollusca occur.

A detailed examination of the means, other than voluntary, by which Mollusca are transported from one place to another hardly comes within the scope of this work. Ocean currents, rivers, floods, cyclonic storms of wind, birds, and even beetles and frogs, play a part, more or less considerable, in carrying living Mollusca or their ova, either separately or in connexion with floating débris of every kind, to a distance from their native home. Accidental locomotion, of one or other of these kinds, combined with the well-known tenacity of life in many species (p. 37), may have contributed to enlarge the area of distribution in many cases, especially in the tropics, where the forces of nature are more vigorous than in our latitudes. The ease with which species are accidentally spread by man increases the probability of such cases occurring without the intervention of human agency, and numbers of instances may be collected of their actual occurrence.[358]

A point, however, which more concerns us here is to remark on the exceedingly wide distribution of the prevailing forms of fresh-water Mollusca. It might have been expected that the area of distribution in the fresh-water forms would be greatly restricted, since they cannot migrate across the land from one piece of water to another, and since the barriers between pond and pond, lake and lake, and one river system and another are, as far as they are concerned, all but insuperable. We might have expected, therefore, as Darwin and Wallace have remarked, to find a great multiplicity of species confined to very restricted areas, since the possibility of communication with the parent stock appears, in any given case, to be so exceedingly remote.

As is well known, the exact reverse occurs. The range, not merely of genera, but even of individual species, is astonishingly wide. This is especially the case with regard to the Pulmonata and Pelecypoda. The genera Limnaea, Planorbis, Physa, Ancylus, Unio, and Cyclas are world-wide. Out of about ten genera of fresh-water Mollusca in New Zealand, one of the most isolated districts known, only one is peculiar. In South Africa and the Antilles no genus is peculiar. In the latter case, this fact is remarkable, when we consider that the same sub-region has at least ten peculiar genera of operculate land Mollusca alone.

To give a few instances of the distribution of particular species:--

Limnaea stagnalis L. occurs in the whole of Europe, and northern Asia to Amoorland, Turkestan, Afghanistan, North Persia, and Kashmir; Greenland, North America from the Atlantic to the Pacific, and from North Canada and British Columbia as far south as Texas. The distribution of L. peregra Müll., L. truncatula Müll., and L. palustris Müll, is almost equally wide.

Planorbis albus occurs in the whole of Europe, and northern Asia to Amoorland, Kamschatka, and Japan; Turkestan, the Altai-Baikal district, Alaska and Greenland, North Canada, and the whole of eastern North America.

The distribution of Anodonta anatina L., Cyclas cornea L., and Pisidium pusillum Gmel. is almost equally wide.

It is evident that the accidental means of transport mentioned above are insufficient to account for the facts as we find them; we are therefore compelled to seek for further explanation. Anything in the nature of a current furnishes a ready means of transport for Mollusca which have obtained a footing in the upper waters of a river, and there is no difficulty in imagining the gradual spread of species, through the agency of floods or otherwise, over a whole river system, when once established at any point upon it. The feeble clinging power of newly-hatched Limnaea has often been noticed as contributing to the chances of their range of distribution becoming extended. Fresh-water Mollusca, too, or their ova, are exceedingly likely, from their extreme abundance, to be transported by water-birds, which fly without alighting from one piece of water to another. Again, the isolation of one river system from another is, in many instances, by no means well marked or permanent, and a very slight alteration of level will frequently have the effect of diverting the supplies of one watershed into another. When we know what enormous oscillations in level have taken place over practically the whole surface of the globe, we can recognise the probability that the whole river system of the earth has been mixed up and reconstructed again and again, with a very thorough blending of adjacent fauna.

It is possible that the very uniform conditions under which fresh-water Mollusca live may have something to do with the uniformity of their distribution and the comparative sameness in their development. There can scarcely be any question that the environments of fresh-water species are in themselves less varied and less liable to fluctuation than those of species whose home is the land. Water is very like water, all the world over; it may be running or motionless, warm or cold, clear or muddy, but the general tendency is for it to be free from extremes of any kind. Even if the surface water of a lake or river freezes, or becomes unusually hot, there is generally plenty of water at a lower stratum which maintains a less extreme temperature, and to which creatures can retire on the first symptoms of a change. From this two results will follow. Not only will the inhabitants of a piece of water not be inclined to vary much from the type, since their whole surroundings, food, etc., continue very much the same, but, if transported by any accident or cataclysm elsewhere, they will be exceedingly likely to arrive at a place which closely resembles their former home in all essentials. Thus the tendency for new types to be formed would be constantly checked, or rather would very seldom arise.

Mr. Belt, while recognising the importance of changes of level as affecting the distribution of fresh-water species, appears to regard the operations of such changes from a rather different point of view to that described above. “I think it probable,” he writes,[359] “that the variation of fresh-water species of animals and plants has been constantly checked by the want of continuity of lakes and rivers in time and space. In the great oscillation of the surface of the earth, of which geologists find so many proofs, every fresh-water area has again and again been destroyed.... Thus species of restricted range were always exposed to destruction, because their habitat was temporary and their retreat impossible, and only families of wide distribution could be preserved.”

* * * * *

The terrestrial surface of the globe has been divided, as indicating the facts of geographical distribution, into six regions--the Palaearctic, Oriental, Australasian, Ethiopian, Nearctic, and Neotropical. To these is sometimes added a seventh, the Neantarctic, consisting of Chili and Patagonia (and certain islands of the south Atlantic); but since the Mollusca of Chili unmistakably form a part of the Neotropical fauna, it seems hardly worth while to recognise a separate region for those of the extreme south of South America, which have no peculiar characteristics.

In certain points the exact limits of these regions, as indicated by the Mollusca, will probably not correspond to those which are marked out by other zoological classes. Wallace’s line, for instance, does not exist, as far as the Mollusca are concerned.

These regions may be further subdivided into sub-regions, thus:--

Regions Sub-regions

{ Septentrional =Palaearctic= { Mediterranean { Central Asiatic

=Oriental= { Indo-Malay { Chinese

{ Papuan =Australasian= { Australian { Polynesian

{ Central African =Ethiopian= { South African { Malagasy

{ American =Nearctic= { Californian

{ Antillean { Central American =Neotropical= { Colombian { Brazilian { Chilian

=A. The Palaearctic Region=

The southern boundary of this region is the northern limit of the African Sahara, the Mediterranean forming no break whatever in its continuity. In Asia this boundary is less well marked, but roughly corresponds to the southernmost of the vast ranges of mountains which border the great tablelands of central Asia. Across Africa the line of desert is well defined; but in the north-east, as the desert approaches more nearly to the sea, the African extent of the region is correspondingly narrowed until it becomes little more than a strip of coast land, scarcely widening even in Lower Egypt. On the Morocco coast, Palaearctic land forms penetrate as far south as Cape Nun.[360] At its eastern extremity the line becomes less well defined, but probably proceeds along the snowy mountains west of Setchouan, the Pe-ling and Tan-sia-shan ranges, so as to include all the high ground of Thibet and of the upper waters of the Hoang-ho, and ultimately reaches its eastern limit at some point on the shores of the Sea of Japan.

The region thus includes all Europe, Africa north of the Sahara, with the Atlantic islands (the Azores, Canaries, etc.), North Arabia, Asiatic Turkey, the greater part of Persia, Afghanistan, Thibet, all Asiatic Russia, and a very large portion of the Chinese empire.

The principal characteristics of the region as a whole are:--

(1) The rich development of Helix, Arion, Limax, Buliminus, and Clausilia.

(2) The comparative absence of land operculates (see map, frontispiece).

(3) The uniform character of the fresh-water fauna.

It is in the southern portion of the region that Helix (in the sub-genera Macularia, Iberus, Pomatia, and Xerophila) and Buliminus (Zebrina, Chondrula, Ena) attain their maximum. In the north, Fruticicola is the characteristic group; in the mountainous districts of the south-east, Campylaea, with Clausilia. The Arionidae have their headquarters in the damp and warm regions of western Europe, but are rare in the south. They only approach the Mediterranean coast in Algeria, near Gibraltar, and in the region between the base of the Pyrenees and the Maritime Alps, and are very poor in species throughout Italy and Sardinia. They are absent from almost the whole of northern Africa, the Mediterranean islands (except Sardinia), the whole Balkan district, the Crimea, Caucasus, and western Asia.[361]

The uniformity of the fresh-water fauna is disturbed only in the extreme south. A few species of Melanopsis, with Neritina, occur in southern Spain and Austria, Galicia, and southern Russia, while a Melania or two (absent from Spain) penetrate the south-eastern parts of Europe as far as Germany. Cyrena begins to replace Cyclas in southern Russia and the Caucasus.

The Palaearctic region falls into three sub-regions:--

(1) The =Northern or Septentrional Sub-region=, i.e. the district north of the line formed by the Pyrenees,[362] Alps, Carpathians, and which, passing to the northward of the Aralo-Caspian district, follows the great central mountain range of Asia until it reaches the Sea of Japan, perhaps somewhere in the neighbourhood of Vladivostok.

(2) The =Mediterranean Sub-region=, i.e. the countries bordering on the Mediterranean, the Black and Caspian Seas, with the Atlantic Islands.

(3) The =Central Asiatic Sub-region=, i.e. Turkestan, Afghanistan, Thibet, and probably the districts of Mongolia and Manchuria.[363]

(1) The =Septentrional Sub-region= has been divided by some writers into two provinces, the European and the Siberian. There seems, on the whole, but little occasion to separate off northern Asia, the characteristic of which is, as will be seen below, rather the gradual disappearance, as we proceed eastward, of European species and genera, than the development of any new and peculiar groups. The remarkable fauna of Lake Baikal stands apart, not only from European, but also from the Siberian types occurring in its immediate neighbourhood.

On the whole, the Septentrional Sub-region is poor in species except those which inhabit fresh water. This fact is probably due to the extreme vicissitudes of temperature which prevail, and it is interesting to notice that the number of land Mollusca appears to touch its lowest point in districts where the annual range of temperature is greatest. On the other hand, in the western portions of the region, where the climate is moist and temperature more equable, the Mollusca are considerably more abundant and varied.

The line which separates the Septentrional from the Mediterranean Sub-region must of necessity be very roughly drawn, and stragglers from the south will be found to make their way northward, and vice versâ, under favouring circumstances of temperature and geological formation. Jordan has noticed[364] that species which in southern countries are not confined to any particular quality of soil are in more northern latitudes found only on limestone, which absorbs more heat than other formations. Conversely, the higher elevations of the Alps, Pyrenees, and even Carpathians are like islands in a sea, and support a thoroughly northern fauna, quite strange to that of the plains below. Thus Helix harpa Say, a completely boreal shell, which is at home in Canada, Sweden, Lapland, and the Amoor district, is found on the Riffel Alp, at a height of 6000 feet.[365] Vertigo arctica Wall., a species abundant in Lapland, North Siberia, Iceland, and Greenland, occurs on the high Alps of the Tyrol.

Circumpolar Species.--A certain number of species are common to the extreme north both of the Palaearctic and Nearctic regions, and are, in fact, circumpolar. The number of these species, however, is so small, not exceeding about 40 species (= 16 genera), that it seems hardly worth while creating a special sub-region for their reception, particularly as no genus is peculiar. At the same time the fact is instructive as illustrating the close connexion of the northern districts of the two regions, a connexion which was no doubt more intimate in recent geological times than it is now.

The circumpolar genera are as follows. The list decisively sets forth the superior hardiness of the fresh-water as compared with the land genera:--

Valvata 1 sp. Bithynia 1 „ Vitrina 1 „ Hyalinia 4 „ Helix 2 „ Patula 2 „ Pupa 3 „ Cionella 1 „ Succinea 1 „ Limnaea 7 „ Planorbis 5 „ Aplecta 1 „ Physa 1 „ Anodonta 1 „ Unio 1 „ Pisidium 1 „

Great Britain.--There are in all about 130 species--83 land, 46 fresh-water; Limnaea involuta (mountain tarn near Killarney) appears to be the only peculiar species. There are 11 Hyalinia, 5 Arion, and 25 Helix, the latter belonging principally to the sub-genera Xerophila, Tachea, Trichia, and Fruticicola. Three Testacella are probably not indigenous, but are now so well established as to reckon in the total. Of the four Clausilia two reach Ireland and one Scotland; two do not occur north of the Forth. There are only two land operculates, one of which (Cyclostoma elegans) occurs in Ireland but not in Scotland, while the other (Acicula lineata) reaches the southern counties of Scotland. Several species, e.g. Helix pomatia, H. obvoluta, H. revelata, H. cartusiana, H. pisana, Buliminus montanus, are restricted to the more southern or western counties; Geomalacus maculosus is confined to a district in south-western Ireland.

The Pleistocene beds of East Anglia contain a number of species now extinct in these islands, whose occurrence appears to indicate a warmer climate than the present. Such are Helix ruderata, H. fruticum, H. incarnata, Clausilia pumila, Unio littoralis, Hydrobia marginata, and Corbicula fluminalis.

Scandinavian Peninsula.--From Norway 121 species in all are recorded, and 148 from Sweden. The milder climate of Norway allows many species to reach a considerably higher latitude than in Sweden, thus in Sweden Limax maximus only reaches 62°, but in Norway 66° 50´. Similarly Arion hortensis and Balea perversa only reach 63° and 61° respectively in Sweden, but in Norway are found as far north as 69° and 67° 50´. Clausilia is represented by 9 species in southern Norway; one of these is found north of the Arctic circle. There are 4 Pupa, 9 Vertigo, and 11 Hyalinia, but Helix dwindles to 14, 9 of which occur north of the Arctic circle. No land operculates are found; Cyclostoma elegans, however, occurs in Jutland and Zealand, which practically form a part of this district.

Iceland.--Eleven species, all Scandinavian, occur. These are Arion 2, Limax 1, Helix 2 (arbustorum L. and hortensis Müll., the latter being found only on the warmer southern coast), Limnaea 1, Planorbis 1, Pisidium 4.

France.--The northern, central, and eastern districts belong to this sub-region, while the southern and western, in which an entirely new element occurs and many northern forms disappear, belong to the Mediterranean. Thus, for instance, Helix pomatia L., H. incarnata Müll., H. fruticum Müll., H. cantiana Mont., H. strigella Drap., H. rufescens Penn., H. plebeia Drap., are not found in southern France. No detailed enumeration of species is at present possible, the efforts of a large number of the leading French authorities being directed to indiscriminate species-making rather than to the careful comparison of allied forms. Perhaps the principal difference between the Mollusca of northern France and those of our own islands is the occurrence of two species of Pomatias. In the more elevated districts of eastern France (the Vosges, Jura, western Alps), a certain number of species occur which are confined to the high grounds of south central Europe. Among these are Helix holoserica Stud., H. personata Lam., H. bidens Chem., H. depilata Drap., H. cobresiana Alt., H. alpina Faure.

The Pleistocene deposits of the valley of the Somme tell the same tale as those of eastern England, containing as they do species and even genera whose northern range is now much more limited. The Eocene fossils from the Paris beds show most remarkable relationships to genera now existing in the West Indies and Central America. Others again indicate affinities with India. Thus we find Ceres, Megalomastoma, and Tudora by the side of Leptopoma, Faunus, and Paludomus.

Germany.--The Mollusca of the plains of northern Germany are few and not striking, and exhibit little difference from those of our own islands. In the mountainous districts of the south and south-east, a number of new forms occur, amongst which are 3 species of Daudebardia, a remarkable carnivorous form, with the general appearance of a Vitrina; 24 of Clausilia, many Pupa, several Buliminus, 3 of the Campylaea group of Helix, stragglers from the Italo-Dalmatian fauna, and 1 of Zonites proper. Our familiar Helix aspersa is entirely absent from Germany. There are only 4 land operculates--Pomatias 2, Acicula 1, Cyclostoma 1, all of which occur exclusively in the south. Bithynella and Vitrella, two minute forms of fresh-water operculates akin to Hydrobia, occur throughout the district.

Northern Russia and Siberia.--This vast tract extends from eastern Germany to the Amoor district. It is exceedingly poor in Mollusca, and is chiefly characterised by the gradual disappearance, as we proceed eastward, of European species. There are a few characteristic Siberian Mollusca, closely allied to European forms, and in the extreme east a new element is introduced in the appearance of types which indicate Chinese affinities. The whole district may be regarded as bounded to the south by a line drawn from Lemberg to Moscow, and thence to Perm; passing south of the Ural mountains, it includes the whole basins of the rivers Obi, Yenesei, and Lena, coinciding with the vast mountain ranges which terminate to the north the table-land of central Asia, at the eastern extremity of which it dips sharply southwards, so as to include the Amoor basin and Corea.

All the larger Helices are wanting, and no land operculates occur. Helix arbustorum L., H. nemoralis Müll., H. lapicida L., H. aculeata Müll., and Hyalinia nitidula Drap., do not appear to occur east of the Baltic; Arion fuscus Müll., Helix strigella Drap., Buliminus obscurus Müll., Clausilia laminata Mont., C. bidentata Bttg., C. plicatula Drap., Viviparus fasciatus Müll., and Neritina fluviatilis L., do not pass the Urals.

In the Obi district (West Siberia) a further batch of European species find their easterly limit. Among these are Helix hispida L., Bithynia tentaculata L., Vivipara vivipara L., Pisidium amnicum Müll., and Unio tumidus Retz. A few distinctly Siberian species now appear, e.g. Ancylus sibiricus Gerst., Valvata sibirica Midd., and Vitrina rugulosa Koch.

The following are among the European species which reach eastern Siberia: Hyalinia nitida Müll., Succinea oblonga Drap., Planorbis vortex L., spirorbis L., marginatus Drap., rotundatus Poir., fontanus Light., Valvata piscinalis Müll., Bithynia ventricosa Leach, and Anodonta variabilis Drap. Here first occur such characteristic species as Physa sibirica West., P. aenigma West., Helix pauper Gld., H. Stuxbergi West., H. Nordenskiöldi West., Planorbis borealis Lov., Valvata aliena West., Cyclas nitida Cless., and C. levinodis West. In the Amoor district a decided Chinese element makes its appearance in a few hardy forms which have penetrated northward, e.g. Philomycus bilineatus Bens., and a few each of the Fruticicola (Chinese) and Acusta groups of Helix. Out of 53 species, however, enumerated from this district, as many as 33, belonging to 18 genera, occur also in Great Britain.

Lake Baikal.--The Mollusca of Lake Baikal exhibit distinct characteristics of their own, which seem to indicate the long-continued existence of the lake in its present condition. Several entirely peculiar genera occur, which are specialised forms of Hydrobia, e.g. Baikalia, Liobaikalia, Gerstfeldtia, Dybowskia, and Maackia; Benedictia alone extends to the basin of the Amoor. Choanomphalus, another peculiar and ultra-dextral (p. 250) genus belonging to the Limnaeidae, appears to be related to the West American Carinifex.

(2) The =Mediterranean Sub-region= is divided into four provinces: (a) The Mediterranean province proper; (b) the Pontic; (c) the Caucasian; and (d) the Atlantidean province.

(a) The Mediterranean province proper is best considered by further subdividing it, with Fischer and others, into separate districts, each of which has certain peculiar characteristics.

(i) The Hispano-Algerian district includes the greater part of the Iberian peninsula, the Balearic Islands, and northern Africa from Morocco to Tunis. The extreme western parts of these districts, including West Morocco, Portugal, Asturias, and south-west France, under the influence of the moist climate caused by the Atlantic, show some peculiar features which, in the view of some, are sufficient to justify their separation from the rest of the Hispano-Algerian portion. Among these is a marked development of the slugs, Testacella, Arion, and Geomalacus, the latter of which occurs even in south-western Ireland.

Spain.--The principal features are the development of the Macularia, Iberus, and Gonostoma groups of Helix, and the occurrence of the remarkable slug Parmacella, which is found in many other parts of the sub-region, and extends eastward as far as Afghanistan. Clausilia has but few species, mostly in the north. There are four species of land operculates, one of which is referred to a genus (Tudora) now living only in the West Indies, but which occurs in the Eocene fossils of the Paris basin. In the south there are several species of Melanopsis and Neritina.

The States of Northern Africa have a thoroughly Mediterranean fauna, whose facies on the whole shows rather more affinity to Spain than to Sicily. The Helices of Morocco and Algeria belong to the same groups as those of southern Spain. Many are of a dead white colour, the better to resist the scorching effect of the sun. Ferussacia is abundant, Geomalacus and Parmacella are represented by a single species each, and there is one Clausilia. According to Kobelt,[366] the original land connexion between southern Spain and Morocco must have been much more extensive than is usually assumed, and probably reached at least to the meridian of Oran and Cartagena. The Mollusca of Oran and Cartagena are, according to him, much more closely related than those of Oran and Tangier, or those of Cartagena and Gibraltar, but at Cartagena some species, which are characteristic of the Mediterranean coasts from Syria westward, disappear, are absent from the rest of Spain and from Morocco, but reappear on the south-western coasts of France. These species may possibly have pushed along that arm of the sea which, when the Straits of Gibraltar were closed as far as the latitude of Oran and Cartagena, united in comparatively recent times the Bay of Biscay with the Gulf of Lions.

The following genera, which do not occur in Spain, have probably spread into northern Africa as far as Algeria, via Sicily and Tunis, namely, Glandina (1 sp.), Daudebardia (1 sp.), Pomatias (2 sp.). Tunis shows strong traces of Sicilian influence, and Kobelt found a colony of snails, of Sicilian affinities, as far west as Tetuan.

The Sahara.--The Algerian Sahara contains, in many places, a sub-fossil Molluscan fauna which appears to show that the district has, in quite recent times, undergone a gradual desiccation. The species are mainly fresh-water, including Melania, Melanopsis, and Corbicula, with here and there valves of Cardium edule, and indicate, on the whole, an affinity with recent Egyptian, rather than North African species. It is probable that a vast series of étangs, or brackish-water lakes, once stretched along this region, and were ultimately connected with the sea somewhere between Tunis and Egypt.

(ii) Southern France.--The southern portion of France bordering on the Mediterranean contains many species, especially of Helix, which do not occur in the centre and north. Amongst these are--

Leucochroa candidissima Drap. Hyalinia olivetorum Gmel. Zonites algirus L. Helix rangiana Desh. „ serpentina Fér. „ niciensis Fér. „ splendida Drap. „ vermiculata Müll. „ melanostoma Drap. „ aperta Born. „ ciliata Ven. „ explanata Müll. „ apicina Lam. „ cespitum Drap. „ Terverii Mich. „ pyramidata Drap. „ trochoides Poir. Ferussacia folliculus Gron. Rumina decollata L. Pupa megacheilos C. and J.

Several species of fresh-water Hydrobia (Bithynella) occur. The district, on the whole, unites certain characteristics derived from northern Italy with those of eastern Spain.

(iii) The Italo-Dalmatian district includes Italy and the neighbouring islands (Corsica, Sardinia, Sicily, Malta), and the regions at the head and north-eastern shores of the Adriatic (Carinthia, Carniola, Croatia, and Dalmatia), the line which separates these latter districts from the fauna of southern Austria, Bosnia, and Servia being very difficult to define.

Italy, with the neighbouring islands, has a rich molluscan fauna. In the sub-Alpine districts of northern Italy the prominent Helix groups are Campylaea, Pomatia, and Anchistoma, which in the south are generally replaced by Iberus, which here attains its maximum development. Large Hyalinia are abundant in the north, and Pomatias and Clausilia are frequent all along the Apennines. Sicily has about 250 species, half of which are peculiar. Helices of the Iberus type abound, but Campylaea is reduced to two species. Many peculiar forms of Clausilia occur, especially a latticed type of great beauty. Ferussacia and Pupa are well represented, and there are one each of Glandina and Daudebardia.

Dalmatia and the adjacent districts are chiefly remarkable for the rich development of Clausilia, which here attains its maximum (nearly 100 species). The Campylaea section of Helix is represented by its handsomest forms, many of which are studded with short hairs. Here too is the headquarters of Zonites proper, which stretches westward as far as Provence, and eastward to Asia Minor; and also of the single European Glandina, which has a similar eastward range, but spreads westward through Italy and Sicily to Algeria, not occurring in southern France. The land operculates are chiefly represented by Pomatias, and among the fresh-water operculates are a Melania and a Lithoglyphus, the latter having probably spread from the basin of the Danube.

(iv) The Egypto-Syrian district extends along the south-eastern shores of the Mediterranean from Tripoli to North Syria, and eastward to the Euphrates valley. Lower Egypt alone belongs to this portion, the fauna of Upper Egypt being of an entirely tropical character, and belonging to the Ethiopian Region.

Lower Egypt.--The Mollusca of Lower Egypt stand in the unique position of belonging, half to the Palaearctic, and half to the Ethiopian Region. The land Mollusca are of a distinctly Mediterranean type, while the fresh-water, directly connected as they are by the great highway of the Nile with regions much farther south, contain a large admixture of thoroughly tropical genera (Ampullaria, Lanistes, Melania, Cleopatra, Corbicula, Cyrena, Iridina, Spatha, Mutela). The Helices, which are not numerous, are rather a mixture of circum-Mediterranean species than of a specially distinctive character. H. desertorum, however, belonging to the group Eremophila, is characteristic. There is a single Parmacella, but the physical features of the country are unfavourable to the occurrence of such genera as Clausilia, Pupa, Hyalinia, and the land operculates.

Syria.--The Mollusca, especially in the more mountainous regions of the north, are much more varied and numerous than those of Egypt. Clausilia is again fairly plentiful, and the Helicidae are represented by some striking forms of the sections Levantina, Pomatia, and Nummulina. Leucochroa has several curious types with a constricted aperture, and the Agnatha are represented by Libania, a peculiar form of Daudebardia. A prominent feature is the occurrence of a number of large white Buliminus of the Petraeus section (Fig. 200). Land operculates appear to be absent, but Melanopsis and Neritina are abundant. The Dead Sea contains no Mollusca, but Lake Tiberias has a rich fauna, including the above-mentioned genera, with a Corbicula and several Unio.

Upper Mesopotamia appears to possess a mixture of Syrian and Caucasian forms, including a Parmacella. Lower Mesopotamia has an exceedingly poor land fauna, but is comparatively rich in fresh-water species, the growing eastern character of which is shown by the occurrence of several Corbicula and Pseudodon, and of a Neritina of a distinctly Indian type.

(b) The Pontic province extends from Western Austria to the Sea of Azof, and includes Austria, Hungary, Roumania, the Balkan peninsula (so far as it does not form part of the Mediterranean sub-region), the islands of the Greek Archipelago, southern Russia and the Crimea, and Asia Minor. It thus practically corresponds to the whole Danube basin, together with the lands bordering on the Black Sea, except at the extreme east, which belongs to the Caucasian sub-region. Fischer separates off Greece, Asia Minor (except the northern coast-line), and the intervening islands, with Crete and Cyprus, as constituting a portion (Hellado-Anatolic) of the Mediterranean sub-region proper. These districts, however, appear to possess scarcely sufficient individuality to warrant their separate consideration.

A prominent characteristic of the Pontic Mollusca is the great abundance of Clausilia and Buliminus. In the islands east and west of Greece Clausilia forms a large proportion of the fauna, each island, however small, possessing its own peculiar forms. The Helices belong principally to the groups Campylaea (which is very abundant in Austro-Hungary), Pomatia (Greece and Asia Minor), and Anchistoma. Macularia is comparatively scarce, but is represented in Greece by one very large form (Codringtonii Gray). Zonites proper has its metropolis in this sub-region, and the Danube basin contains one or two species of Melania and Lithoglyphus. Buliminus is abundant throughout the sub-region, in the sub-genera Zebrina, Napaeus, Mastus, and Chondrula. Several striking forms of Zebrina (Ena) are peculiar to the Crimea.

(c) The Caucasian Province.--The limits of this province can hardly be exactly defined at present. It appears, however, to include the whole line of the Caucasus range, Armenia, and North Persia.

The land Mollusca are abundant and interesting. Among the carnivorous genera are four species of Daudebardia, a Glandina, and three peculiar forms of naked slug, Pseudomilax, Trigonochlamys, and Selenochlamys. There is a single Parmacella, the same species as the Mesopotamian, and a good many forms of Limax. Vitrina and Hyalinia are well represented, and the predominant groups of Helix are Euloto, Cartusiana, Xerophila, and Fruticocampylaea, the last being peculiar. Clausilia and Pupa are rich in species, together with Buliminus of the Chondrula type. One Clausilia of the Phaedusa section, together with a Macrochlamys (Transcaspian only), a Corbicula, and a Cyclotus, show marked traces of Asiatic affinity. There is one species each of Acicula and Cyclostoma, and one of Pomatias.

The Caspian Sea, like Lakes Baikal and Tanganyika, is distinguished by the possession of several remarkable and peculiar genera. The sea itself, the waters of which are brackish, is 80 feet below the level of the Black Sea, and is no doubt a relict of what formed, in earlier times, a very much larger expanse of water. Marine deposits containing fauna now characteristic of the Caspian, have been found as far north as the Samara bend of the Volga. It is probable, therefore, that in Post-pliocene times an arm of the Aralo-Caspian Sea penetrated northward up the present basin of the Volga to at least 54° N. The Kazan depression of the Volga (55° N.) also contains characteristic Caspian fossils.[367] According to Brusina,[368] the Caspian fauna, as a whole, is closely related to the Tertiary fauna of southern Europe.

Twenty-six species of univalve Mollusca, the majority being modified forms of Hydrobia, have been described from the Caspian, namely, Micromelania (6), Caspia (7), Clessinia (3), Nematurella (3), Lithoglyphus (1), Planorbis (1), Zagrabica (1), Hydrobia (2), Neritina (2). The bivalves are mostly modified forms of Cardium (Didacna, Adacna, Monodacna), which also occur in estuaries along the north of the Black Sea. A form of Cardium edule itself occurs, and numberless varieties of the same species are found in a semi-fossil condition in the dry or half dry lake-beds, which are so abundant throughout the Aral district.

(d) The Atlantidean province consists of the four groups of islands, the Madeiran group, the Canaries, the Azores, and the Cape Verdes.

The Madeiran group contains between 140 and 150 species of Mollusca which may be regarded as indigenous, the great majority of which are peculiar. Only 11 species are common to Madeira and to the Azores, and about the same number, in spite of their much greater proximity, to Madeira and the Canaries. No less than 74 species, or almost exactly one-half, belong to Helix, and 9 to Patula. A considerable number of the Helices are not only specifically but generically peculiar, the genera bearing close relationship to those occurring in the Mediterranean region. As a rule they are small in size, but often of singular beauty of ornamentation. Various forms of Pupa are exceedingly abundant (28 sp.), as is also Ferussacia (12 sp.). There are also 3 Clausilia (which genus occurs on this group alone), and 3 Vitrina (a genus which occurs on all the groups). The land operculates are represented solely by 4 Craspedopoma, which is common to all the groups except the Cape Verdes.

The Canaries have about 160 species, only about a dozen of which are not peculiar. As many as 75 of these belong to Helix (the sub-genera being very much the same as in the Madeiran group), and 11 to Patula. There is 1 species of Parmacella (which occurs in this group alone), and 6 of Vitrina, of considerable size. A remarkable slug (Plectrophorus) was described from Teneriffe by Férussac many years ago, but it has never been rediscovered, and is probably mythical, or wrongly assigned. Buliminus (Napaeus) has as many as 28 species, all but one being peculiar, and Ferussacia 7. Cyclostoma has two indigenous species, which, with one Hydrocena and one Craspedopoma, make up the operculate land fauna.

The Azores are comparatively poor in Mollusca, having only 52 species, nearly two-thirds of which are peculiar. Helix has 15 species, Patula 4, and Pupa 8. Ferussacia, so abundant in Madeira and the Canaries, is entirely absent, its place being taken by Napaeus (7 sp.), which is curiously absent from Madeira, but richly represented in the Canaries. There are 7 Vitrina, while the land operculates consist of one each of Craspedopoma and Hydrocena. A singular slug (Plutonia), with an ancyliform internal shell, is said to occur. The group was long believed to possess no fresh-water Mollusca, but two species (one each of Pisidium and Physa) have recently been discovered.

The Cape Verdes, owing to the extreme dryness of their climate, are poor in land Mollusca. There are 11 Helix, nearly all of which belong to the group Leptaxis, which is common to Madeira and the Canaries. Ferussacia is absent, Buliminus is represented by a single species, and there are no land operculates. Ethiopian influence, however, as might be expected from the situation of the group, is seen in the occurrence of an Ennea, a Melania, and an Isidora.

It will be noticed how little countenance the molluscan fauna of these island groups gives to any theory of an Atlantis, any theory which regards the islands as the remains of a western continent now sunk beneath the ocean. Had ‘Atlantis’ ever existed, we should have expected to find a considerable proportion of the Mollusca common to all the groups, and perhaps to Europe as well, and there would apparently be no reason why a genus which occurred in one group should not occur in all. As a fact, we find the species extremely localised throughout, and genera occur and fail to occur in a particular group without any obvious reason. All the evidence tends to show that the islands are purely oceanic, and have been colonised from the western coasts of the Mediterranean, i.e. from the direction of the prevailing currents and winds.

(3) =Central-Asiatic Sub-region.=--The countries included in this vast sub-region are Turkestan, Songaria, Afghanistan, including the Pamirs, Western Thibet, and probably Mongolia. Kashmir belongs to the Indian fauna. At present the whole district is very imperfectly known; indeed, it is only at a few points that anything like a thorough investigation of the fauna has been made. It is therefore almost premature to pronounce any decided opinion upon the Mollusca, but all the evidence at present to hand tends to show that they belong to the Palaearctic and not to the Oriental system. This is especially the case with regard to the fresh-water Mollusca, many of which are specifically identical with those occurring in our own islands. A slight admixture of such widely distributed types as Corbicula and Melania occurs, but it is not sufficient to disturb the general European facies of the whole. It is possible that eventually the whole district may be regarded as a sub-region combining certain characteristics of the eastern portions of the Mediterranean basin with an extension of the septentrional element, due to higher elevation and more rigorous climate. The principal features in the land Mollusca appear to be the occurrence of a number of Buliminus of the Napaeus group, a few Parmacella (Afghanistan being the limit of the genus eastward), Clausilia, Pupa, Limax, and Helix, with several stray species of Macrochlamys.

=B. The Oriental or Palaeotropical Region=

This region includes all Asia to the south of the boundary of the Palaearctic region, that is to say, India, with Ceylon, Burmah, Siam, and the whole of the Malay Peninsula, China proper, with Hainan and Formosa, and Japan south of Yesso. It also includes the Andamans and Nicobars, and the whole of Malaysia, with the Philippines, as far eastward as, and including Celebes with the Xulla Is., and the string of islands south of the Banda Sea up to the Ké Is. The Moluccas, in their two groups, are intermediate between the Oriental and Australasian regions.

In this vast extent of land two distinct centres of influence are prominent--the Indian and the Chinese. Each is of marked individuality, but they differ in this essential point, that while the Chinese element is decidedly restricted in area, being, in fact, more or less confined to China itself and the adjacent islands, the Indian element, on the other hand, extends far beyond continental Asia, and embraces all the Malay islands to their farthest eastward extent, until it becomes overpowered by the Papuan and Australian fauna. Upper Burmah, with Siam, forms a sort of meeting-point of the two elements, which here intermingle in such a way that no very definite line of demarcation can be drawn between them.

Thus we have--

{ { (a) Indian Province { 1. Indo-Malay Sub-Region { (b) Siamese Province =Oriental Region= { { (c) Malay Province { { (d) Philippine Province { { { (a) Chinese Province { 2. Chinese Sub-Region { (b) Japanese Province

The Indo-Malay fauna spreads eastward from its metropolis, but has practically no westward extension, or only such as may be traced on the eastern coasts of Africa and the off-lying islands. There appears to exist no other case in the world where the metropolis of a fauna is so plainly indicated, or where it lies, not near the centre, but at one of the ends of the whole area of distribution.

Comparing the two sub-regions, the Chinese is distinguished by the great predominance of Helix, while in the Indo-Malay sub-region Nanina and the related genera are in the ascendancy. In India itself there are only 6 genera of true Helicidae, poorly represented in point of numbers; in China there are at least three times this amount, most of them abundant in species. The Indo-Malay sub-region, on the other hand, is the metropolis of the Naninidae, which abound both in genera and species. In the Chinese sub-region Clausilia attains a development almost rivalling that of S.E. Europe, while in India there are scarcely a dozen species. A marked feature of the Indo-Malay sub-region is the singular group of tubed land operculates (Opisthoporus, Pterocyclus, etc.). In China the group is only represented by stragglers of Indian derivation, while the land operculate fauna, as a whole, is distinctly inferior to the Indian. Another characteristic group of the Indo-Malay region is Amphidromus, with its gaudily painted and often sinistral shell; the genus is entirely absent from China proper and Japan, where its place is taken by various small forms of the Buliminus group. Fresh-water Mollusca, especially the bivalves and operculates, are far more abundant in the Chinese sub-region than in the Indo-Malay.

(1) The =Indo-Malay Sub-region=.--(a) The Indian Province proper includes the peninsula of Hindostan, together with Assam and Upper and Lower Burmah. To the east and extreme north-east, the boundaries of the province are ill-defined, and the fauna gradually assimilates with the Siamese on the one hand and the Chinese on the other. Roughly speaking, the line of demarcation follows the mountain ranges which separate Burmese from Chinese territory, but the debatable ground is of wide extent, and Yunnan, the first Chinese province over the border, has many species common with Upper Burmah.

The gigantic ranges of mountains which bound the sub-region to the north-west and north limit the extension of the Indian fauna in those directions in a most decisive manner. There is no quarter of the world, even in W. America, where a mountain chain has equal effect in barring back a fauna. In the north of Kashmir, where the great forests end, there is a most complete change of environment as the traveller gains the summit of the watershed; but Kashmir itself distinctly belongs to the Indian and not the Palaearctic system. The great desert to the south of the Punjab is equally effective as a barrier towards the west.

The Mollusca of India proper include a very large number of interesting and remarkable genera. India is the metropolis of the great family of the Naninidae, or snails with a caudal mucus-pore, which are here represented by no less than 14 genera and over 200 species. The genera Macrochlamys, Sitala, Kaliella, Ariophanta, Girasia, Austenia, and Durgella are at their maximum. Helix is scarcely represented, containing only about 30 inconspicuous species (leaving Ceylon out of account). Buliminus is abundant, especially in the north. The Stenogyridae are represented by Glessula, which is exceedingly abundant in India, but has only a few straggling representatives in the rest of the Oriental region. Among the Pupidae is the remarkable form Boysia, with its twisted upturned mouth, while Lithotis is a peculiar form allied to Succinea, to which group also probably belongs Camptonyx, a limpet-like form with a very small spire, peculiar to the Kattiawar peninsula. Camptoceras, an extraordinarily elongated sinistral shell, with a loosely coiled spire, is peculiar to the N.W. Provinces.

Among the fresh-water pulmonates is an Ampullarina, a genus only known elsewhere from the Fiji Is. and E. Australia. Cremnoconchus is a form of Littorina, peculiar to the W. Ghâts, which has habituated itself to a terrestrial life on moist rocks many miles from the sea. The fresh-water operculates include the peculiar forms Mainwaringia, from the mouth of the Ganges (intermediate between Melania and Paludomus), Stomatodon, Larina, Fossarulus, Tricula, and others. The bivalves are neither numerous nor remarkable; Velorita, a genus of the Cyrenidae, is peculiar.

The land operculate fauna of India is singularly rich and varied. About 25 genera, and at least 190 species, occur. Here we find the metropolis of Cyclophorus among the larger forms, and of Diplommatina and Alycaeus among the smaller. A large proportion of the operculate genera are quite peculiar to the extreme south of India and Ceylon. The appearance of a few species of the European genus Pomatias is very remarkable.

The carnivorous genera are poorly represented. A few Ennea occur, while Streptaxis is practically confined to the extreme south and north-east.

Land and Fresh-water Mollusca of India proper

Streptaxis 9 Ennea 8 Helicarion 15 Girasia 14 Austenia 11 Ibycus 1 Africarion 2 Durgella 4 Ariophanta 15 Xesta 8 Macrochlamys 78 Microcystis 7 Sitala 20 Kaliella 35 Hemiplecta 15 Sesara 3 Trochomorpha 5 Trochomorphoides 1 Parmacella (?) 1 Tebennophorus 1 Anadenus 4 Plectopylis 11 Plectotropis 3 Trachia 12 Thysanota 1 Camaena 1 Amphidromus 2 Boysia 1 Petraeus 14 Cerastus 6 Rachis 5 Cylindrus 1 Pupa 15 Hapalus 4 Clausilia 10 Subulina 2 Opeas 6 Glessula 49 Geostilbia 3 Succinea 11 Lithotis 2 Vaginula 1 Camptonyx 1 Coelostele 1 Carychium 3 Ancylus 1 Limnaea 7 Camptoceras 3 Planorbis 10 Ampullarina 1 Melania 17 Mainwaringia 1 Paludomus 10 Stomatodon 1 Larina 1 Cremnoconchus 3 Fairbankia 2 Tricula 1 Bithynia 9 Fossarulus 1 Stenothyra 3 Vivipara 4 Valvata 1 Ampullaria 4 Assiminea 9 Acmella 2 Pomatias 4 Diplommatina 63 Pupina 1 Streptaulus 1 Coptochilus 3 Alycaeus 49 Lagochilus 1 Cyclophorus 12 Scalaina 1 Micraulax 2 Jerdonia 10 Spiraculum 4 Otopoma 1 Cyclotopsis 2 Georissa 1 Modiola 1 Scaphula 1 Unio 40 Solenaia 1 Cyrena 13 Sphaerium 1 Pisidium 5 Velorita 2 Tanysiphon 1 Novaculina 1 Nausitora 1

The Cingalese district, which almost approaches the character of a distinct province, presents several remarkable points of dissimilarity from the rest of India. It consists of the island of Ceylon, and of a portion of S. India whose exact limits have yet to be defined. It appears, however, that the Western or Malabar coast, with the hills parallel to it, is more akin to Ceylon than the Eastern or Coromandel coast. The Travancore, Malabar, and S. Canara districts, with the Palnai, Anamalai, and Nilghiri Hills, are markedly Cingalese, while there seems to be no distinct evidence of similar relationship on the part of the Madras or even the Cuddalore district.

Among the principal features of the Cingalese district is the occurrence of three peculiar genera of Helix, one (Acavus) large and finely coloured, another (Corilla) smaller, with a singularly toothed aperture. While the Corilla group shows relations with Plectopylis and other Burmese and Siamese sub-genera Acavus (Fig. 204) is totally distinct from any other Indian form, and shows signs of close relationship, in the great size of the embryonic shell, to the Helices of Madagascar (p. 335). In Ceylon the group is entirely isolated, and its occurrence, besides decisively separating that island from India, Burmah, and Siam, forms a most interesting problem in the history of distribution. Eurystoma, with a single species (E. vittata Müll.), is also peculiar.

As usual when Helix gains ascendancy, the Naninidae retrogress. Durgella, Austenia, and Girasia are absent altogether, while Macrochlamys, Sitala, Kaliella, etc., are present in greatly diminished numbers. The sub-genus Beddomea is peculiar, a form directly related to Amphidromus (Siam and Malacca). The fresh-water operculate Philopotamis is peculiar, but for one species found in Sumatra; while Tanalia is quite peculiar. But the forms which, next to the Helices, most emphasise the separation of the Cingalese district are the land operculates. There are eleven genera or sub-genera of land operculates which do not occur in the rest of India proper. Two (Aulopoma and Cataulus) are quite peculiar, while the other nine are represented in Burmah, Siam, and the Malay islands, but not in India. On the other hand, Diplommatina and Alycaeus, so profusely abundant in India, have not yet been discovered in Ceylon. Among the slugs, Tennentia is a peculiar genus, whose nearest relation occurs in the Seychelles.

Genera and Subgenera occurring in the Cingalese District, but not in N. and Central India

Streptaxis Tennentia Acavus Eurystoma Corilla Beddomea Philopotamis Tanalia Theobaldius Leptopomoides Craspedotropis Pterocyclus Aulopoma Ditropis Cyathopoma Mychopoma Cataulus Nicida Opisthostoma

The district consisting of Upper Burmah, Pegu, Tenasserim, and Aracan, while essentially a part of the Indian province, contains several Siamese genera which are not found in India proper, as well as several which are at present peculiar. Amongst the former category are, of Helicidae, a single representative each of the genera Camaena (Siamese and Chinese) and Aegista (Chinese). Influence of the same kind is seen in the increased numbers of Plectopylis (14 sp.) and Plectotropis (5 sp.), of Clausilia (10 sp.) and Amphidromus (5 sp.), and of the large tubed operculates (11 sp. in all). Sesara and Sophina among the Naninidae are strange to India, while Hyalimax is common only to the Andamans, Nicobars, and Mascarene Is. Hypselostoma (Fig. 202, A) is a most remarkable genus of the Pupidae, reminding one of Anostoma of the New World. It is peculiar to the peninsula, but for one species in the Philippines. Among the Pupinidae, we have the peculiar Raphaulus and Hybocystis (Fig. 205), a very remarkable form, of which another species occurs at Perak. Two Helicina mark the most westward extension of the genus on the mainland. In the extreme north of Upper Burmah, Indian and Chinese forms intermingle.

The Burmese district, together with the Indian and Siamese provinces, is pre-eminently the home of a group of Mollusca, originally of marine origin, which have permanently habituated themselves to a brackish or fresh-water existence. They belong to widely different families, and even Orders. Besides Cremnoconchus mentioned above, we have, among the bivalves, Novaculina, a Solen living in fresh water in the Ganges, Irawadi, and Tenasserim estuaries; Scaphula, an Arca, one species of which occurs in the Ganges hundreds of miles above the tide-way (see Fig. 9, p. 14); and Martesia, a Pholas from the Irawadi Delta. Clea (which also occurs in Java and Sumatra) is probably an estuarine Cominella; a Tectura has earned the name fluminalis from its exclusive residence in the Irawadi R.; Iravadia is probably a Rissoina of similar habits, occurring from Ceylon round to Hong-Kong; Brotia is a Cerithium from an affluent of the River Salwin, and Canidia is a Nassa, occurring in the embouchures of rivers from India to Borneo. Nowhere else in the world is there such a collection--not exhausted by this list--of marine forms caught in process of habituation to a fresh-water or even a land existence.

The Andaman and Nicobar Islands possess no peculiar features in their land Mollusca. They are closely related to the adjacent coasts of Lower Burmah. Amphidromus (2 sp.) occurs in the Andamans alone, and Clausilia (2 sp.) in the Nicobars alone, while Hyalimax occurs in both groups. A remarkable Helix (codonodes Fér.) from the Nicobars appears to find its nearest relations in the isolated group from Busuanga and Mindoro (p. 315). Land operculates are abundant, in the Nicobars actually outnumbering the pulmonates (28 to 22). Helicina and Omphalotropis, genera characteristic of small islands, are found on both groups.

(b) The Siamese Province includes the area occupied by the districts known as Siam, Laos, Cambodia, Cochin China, Annam, and Tonquin. Along the whole of its northern frontier, the zoological is no more than a political boundary, while on the east the mountain ranges which part Siam from Pegu and Tenasserim are not of sufficient height to offer any effective barrier to distribution. The province is accordingly qualified to a considerable extent by Indian and Chinese elements.

Streptaxis is, but for three Ennea, the sole representative of the carnivorous genera, and attains its maximum in the Old World. Partly owing to Chinese influence, the Helicidae, with 11 genera and 46 species, begin to regain their position as compared with the Naninidae (12 genera, 54 species). Of the Helicidae, Acusta and Hadra appear now for the first time, and, with Plectotropis, Stegodera, and Clausilia, form a marked Chinese element. Amphidromus, with 33 species, is the most characteristic land pulmonate. Several genera, whose nucleus of distribution lies among the islands farther east, appear to have penetrated as far as these coasts. Such are Chloritis, Camaena, and Obbina among the Helicidae, Trochomorpha, and, of the operculates, Helicina.

Land operculates are very richly developed. In all, there are 17 genera and 104 species known. The tubed operculates attain their maximum, and Cyclophorus is even more abundant than in India. Fresh-water bivalves abound. Dipsas and Pseudodon are common to China, and Unio and Anodonta are profusely represented. A curious resemblance to S. America appears in this group, a single Mycetopus occurring, the only species not Brazilian, while Arconaia appears very closely to approach the Hyria of the same locality. Several genera of the Hydrobia type (Pachydrobia, Jullienia, Chlorostracia) are peculiar.

Land and Fresh-water Mollusca of the Siamese Province

Streptaxis 20 Ennea 3 Helicarion 7 Microcystis 3 Sesara (?) 1 Medyla 1 Xesta 4 Macrochlamys 6 Kaliella 5 Hyalinia (?) 1 Hemiplecta 14 Rhysota 2 Trochomorpha 6 Trochomorphoides 3 Plectopylis 5 Stegodera 2 Plectotropis 12 Trachia 3 Fruticicola 2 Acusta 2 Chloritis 8 Dorcasia 1 Camaena 5 Hadra 5 Obbina 1 Amphidromus 33 Bocourtia 2 Buliminus 4 Hypselostoma 2 Tonkinia 1 Clausilia 15 Opeas 7 Spiraxis (?) 2 Subulina 1 Succinea 4 Vaginula 7 Limnaea 7 Planorbis 6 Canidia 13 Melania 39 Faunus 1 Bithynia 9 Wattebledia 1 Stenothyra 4 Hydrobia 1 Pachydrobia 9 Jullienia 6 Lacunopsis 6 Chlorostracia 4 Vivipara 39 Valvata 1 Ampullaria 15 Assiminea 7 Procyclotus 6 Dasytherium 2 Opisthoporus 5 Rhiostoma 7 Myxostoma 1 Pterocyclus 7 Cyclophorus 28 Leptopoma 10 Lagochilus 6 Pupina 8 Hybocystis 3 Alycaeus 6 Cataulus (?) 1 Diplommatina 2 Helicina 4 Georissa 2 Modiola (f. w.) 2 Dreissensia 3 Anodonta 17 Mycetopus 1 Pseudodon 18 Dipsas 4 Unio 64 Arconaia 1 Cyrena 6 Batissa 1 Corbicula 35

(c) The Malay Province includes the peninsula of Malacca south of Tenasserim, and the series of islands beginning with Sumatra and stretching eastward up to the Ké Is., besides Borneo and Celebes. The Philippines form a separate province.

The Malay province is singularly poor in representative forms, whether we regard it as a whole or consider the islands separately. Not a single genus, with the exception of Rhodina (Malacca), appears to be peculiar. The contrast with the West Indies is in this respect very striking. Java, for instance, which is well explored, and almost exactly eleven times the size of Jamaica, has about 100 species of land Mollusca, while Jamaica has about 460.

This want of individuality in the land Mollusca of the Malay islands is accounted for by a consideration of the sea depths which separate them from the Asiatic mainland. The accompanying map, the red line on which is intended to show what would be the result of an elevation of the sea bottom for no greater amount than 100 fathoms, exhibits clearly the fact that these islands are practically a part of Asia, a large stretch of very shallow sea extending between Siam and the greater part of the north-west coast of Borneo.

In all probability the three great islands of Sumatra, Java, and Borneo were united with the mainland of Asia, and with one another, at a period, geologically speaking, comparatively recent. This follows from the general uniformity of their land Mollusca, both as regards one another and as regards the mainland. Nor do the smaller members of the island series--Bali, Lombok, Sumbawa, Flores, Timor, and Timor Laut--show any marked individuality in the possession of peculiar genera. Wallace’s line is absolutely non-existent, so far as the land Mollusca are concerned. The really noticeable break in distribution comes with the Aru Is., for while the Tenimber group (Timor Laut, etc.) are decidedly Malay, and the Ké Is., in the poverty of our information, uncertain, the Aru Is. are as Papuan as New Guinea itself. The profound depths of the Banda Sea to the north, and the Timor Sea to the south, appear to have kept the islands from Flores to Timor Laut free from the intrusion of any Moluccan or any considerable Australian element. The Moluccas, as has been already remarked, besides possessing considerable peculiarities of their own, unite a mixture of the Malay and Papuan elements, and serve as a sort of debatable ground for the meeting of the two.

The Malay peninsula is practically another island of somewhat the same shape and general trend as Sumatra, and about one-half the size. Its general relations--and the remark applies to the great Sunda Islands as well--appear to be rather more with Burmah, Tenasserim, and even the Cingalese district, than with Siam. Points of connexion between Ceylon and Sumatra, and Ceylon and Borneo, have already (p. 304) been brought out.

It seems not impossible, from the point of view of the land Mollusca only, that the Sunda Islands may at one time have stretched much farther into the Bay of Bengal, prolonged, perhaps, into what are now the Andaman and Nicobar groups, while Ceylon and the western side of the Deccan, united into one continuous piece of land, and possibly separated from N. India by a wide stretch of sea, extended farther eastward in a long island, or series of islands.

Java, from its Mollusca, does not appear to hold the comparatively isolated position which its mammals and birds seem to indicate. Borneo, on the other hand, is more Siamese than Java or Sumatra in respect of a group whose metropolis is Siam, namely, the tubed operculates; for while that section is represented by 3 species in Sumatra and only 2 in Java, in Borneo it has as many as 19, Rhiostoma not occurring in the two former islands at all. Alycaeus, Lagochilus, Pupina, and Cyclophorus are found throughout, but Hybocystis (Malacca, 1 sp.) does not quit the mainland. Borneo is remarkably rich in land operculates, especially noticeable being the occurrence (11 sp.) of Opisthostoma (Fig. 208), a most extraordinary form of land shell (Ceylon, Siam), of Diplommatina (17 sp.), and Raphaulus. The occurrence of a single Papuina (Moluccas eastward) is very remarkable.

Amphidromus is a genus characteristic of the great Sunda Islands, attaining its maximum in Java (12 sp.). The Indian Glessula still has one species each in Sumatra, Java, and Borneo. One species of Streptaxis[369] occurs in Malacca, but Ennea (3 sp.) reaches as far east as Borneo and the Philippines. Parmarion, Helicarion, Ariophanta, and other groups of the Naninidae are well represented. Hemiplecta and Xesta are abundant and large, while the Rhysota of Borneo contain some huge sinistral forms. Rhodina is a remarkable form from Malacca, whose exact generic position is not yet settled. Clausilia has a few species on all the islands, the last occurring on Ternate, and a single Papuina (Moluccas and N. Guinea) occurs in Borneo.

The Island of Celebes marks the beginning of a distinct decrease in the Indo-Malay element. The Naninidae lose ground, in proportion to the Helicidae, Macrochlamys, for instance, being represented by only one species, and Hemiplecta by four. Other characteristic genera of the Indian region dwindle, such as Amphidromus, Clausilia, the tubed operculates, and Cyclophorus, while Sitala, Kaliella, Glessula, and Plectotropis disappear altogether. Comparing the total numbers of Naninidae and Helicidae from Sumatra to New Guinea, we obtain this interesting result:--

Sumatra Java Borneo Celebes Moluccas N. Guinea Nanina (all genera) 26 32 51 22 36 40 Helix (all genera) 7 11 13 14 55 91

It will be noticed that the proportion of Naninidae to Helicidae, which has been nearly 4 to 1 in Sumatra, falls to 3 to 1 in Java, and rises again to 4 to 1 in Borneo (showing the essentially continental character of the island); in Celebes it further falls to 3 to 2, while in the Moluccas the scale turns and Helix has the advantage by about 8 to 5, and in N. Guinea by more than 2 to 1.

There is the same absence of marked features of individuality in Celebes as in the islands dealt with above. Not a single genus is peculiar. The nature of the sea bottom between Borneo and Celebes, with its indications of a somewhat broad bridge over an otherwise deep channel of separation, would seem to account for and suggest the true explanation of the facts as they stand. At the same time, there are indications of a certain amount of contrast between N. and S. Celebes. The Indian element, which constitutes the preponderating majority of the fauna, is common to north and south alike. But the north part of the island, in which Obba and Obbina occur, shows decided relationship with the Philippines, while the occurrence of three Chloritis and one Planispira tend to approximate S. Celebes rather with the Moluccas.

The islands eastward of Java, from Bali to Timor Laut and the Tenimber Is., present no trace of individual peculiarities; they simply carry on the Indo-Malay fauna as though along a great peninsula. Even Timor, surrounded as it is on all sides by sea of profound depth, shows no sign of possessing even one peculiar genus. Amphidromus, perhaps the most characteristic of all Indo-Malay genera, occurs throughout, diminishing in numbers as we go eastward (Bali, Lombok, and Sumbawa 4 sp., Timor 2 sp., Timor Laut 1 sp.), while Plectotropis reaches no farther than Flores and Timor. The tubed operculates are altogether wanting. In Timor Laut we have Moluccan influence appearing in 3 Chloritis, and there is one (supposed) Corasia. Two Helices of a marked Australian type (Rhagada) occur, one in Flores, the other on Dama I., south-west of Timor. The configuration of the sea bottom (see map) would lead us to believe that the north-west coast of Australia once stretched a good deal nearer to these islands.

The Moluccas, taken as a whole, constitute a transition region between the Indo-Malay and the Papuan faunas, uniting, to a very considerable extent, the features of both. They fall into two well-defined groups. The northern, or Ternate group, consists of Gilolo (Halmahera), Batchian, and the outlying islands as far south as and including Obi major. The southern, or Amboyna group, consists of Buru, Ceram, Amboyna, and the chain of islands to the south-east of Ceram, as far as, and including the Ké Is.

The Ternate group shows decidedly closer relations with New Guinea than the Amboyna group. Thus, among the Helices, the markedly Papuan genus Papuina is represented by 7 species in the Ternate group, but by 1 in the Amboyna group. Again, the Cristigibba section of Planispira, which is a Papuan form, has 4 representatives in the northern group, but only 1 in the southern. Certain points of connexion with Celebes come out in the southern group which are wanting in the northern; thus of Chloritis there are 8 species in Amboyna, 0 in Ternate, 3 in Celebes.

In the Moluccas the Helicidae, for the first time as we move eastward from India, gain the ascendancy over the Naninidae, the numbers being, Helix 55, Nanina 36. If we take the groups separately, we find that in the Amboyna group the proportion is 22 to 23, while in the Ternate group it is 33 to 13, an additional proof that the Amboyna group is far less Papuan than the Ternate. Of Planispira, the most characteristic sub-genus of Helix, there are 12 species in the Ternate group, and 5 in the Amboyna. The section Phania, which contains 4 species of the finest Helices known, is quite peculiar to the Ternate group. One species of Obbina, a sub-genus markedly Philippine, occurs in each group. Several of the Indo-Malay land operculates (e.g. Ditropis) reach their limit here, and here too we have the last Clausilia (strangely absent from the Amboyna group). Amphidromus is not reported on sufficient authority to warrant its insertion in the list.

Land Mollusca of the Moluccas. (T = Ternate, A = Amboyna[370] group)

Helicarion 1 A Euplecta 1 A Xesta 6 A, 4 T Macrochlamys 1 A Lamprocystis 4 A, 2 T Macrocycloides 4 A Sitala 1 A Kaliella 3 A, 1 T Trochomorpha 3 A, 3 T Endodonta 1 A Patula 1 A Plectotropis 1 T Eulota 1 A Chloritis 8 A Planispira 5 A, 12 T Cristigibba 1 A, 4 T Obbina 1 A, 1 T Phania 4 T Albersia 3 T Camaena 1 T Papuina 1 A, 7 T Pupa 3 A Vertigo 2 A Clausilia 1 T Opeas 4 A, 4 T Subulina 1 A Tornatellina 1 A Vaginula 1 A Melania 18 A, 4 T Faunus 1 A Vivipara 1 A Acmella 1 A Diplommatina 4 A, 2 T Registoma 1 T Pupinella 1 A Callia 2 A Leptopoma 4 A, 5 T Lagochilus 1 A, 1 T Ditropis 3 A Cyclotus 4 A, 6 T Omphalotropis 3 A Georissa 1 T Helicina 6 A, 3 T

(d) The Philippine Province.--In the extraordinarily rich development of their Mollusca, the Philippines form a remarkable contrast with the poverty of the adjacent Malay islands. No less than 727 species of land Mollusca alone are known from the group, amongst which are included some of the finest and handsomest forms yet discovered. The main features of the fauna are Indo-Malay, with the addition of a certain Australasian element, and a remarkable development of individual characteristics.

The principal indigenous feature is the profuse abundance of the genus Cochlostyla, a group of large and elegant land shells, partly helicoid, partly bulimoid in shape, many of the species of which are covered with a curious hydrophanous epidermis. They are in the main of arboreal habits, living in the tops of the enormous forests which cover the greater part of the islands. As many as 247 species, belonging to 15 sub-genera, have been described.

The distribution of the sub-genera of Cochlostyla on the different islands of the Philippine group affords important evidence on the geological relation of the islands to one another. Thus we find Orthostylus and Hypselostyla occurring in the central islands and S. Luzon, but not in Mindanao or Mindoro; we find Chrysalis peculiar to Mindoro, Prochilus to Mindoro and the Cuyos, Ptychostyla to Luban, all these being sub-genera of very marked characteristics. Six out of the fifteen sub-genera are entirely absent from Mindanao, although occurring on the islands in the immediate vicinity. The little group Tablas-Romblon-Sibuyan are entirely deficient in certain sub-genera which occur on the islands surrounding them on all sides.[371]

Other forms peculiar to the Philippines are Diaphora, a section of Ennea with a curiously produced mouth, and several sub-genera of the Naninidae (Vitriniconus, Vitrinoidea, Hemitrichia). The great Rhysota here find their metropolis. Another very marked group of Helix is Obbina, 19 of the 25 known species being peculiar.

The Helicidae proper of the Philippines are still held in check, as in the greater part of the Indian region, by the Naninidae. The single Trachia and Plectotropis, and the 2 species each of Plectopylis and Satsuma, indicate affinities with Indo-China. Further important Indian relationships are seen in the great Nanina and Cyclophorus, which here attain almost Indian dimensions; in Kaliella (8 sp.), Sitala (2), Clausilia (1). Among the operculates we still have 1 Alycaeus and 1 Coptochilus. Singularly enough, several Indian genera which occur here are not found in the intervening islands of Borneo, Sumatra, or Java, e.g. Streptaxis, Hypselostoma, Ditropis, Acmella, and Cyathopoma. The curiously tubed Malay operculates, Opisthoporus, etc., fail to reach the Philippines proper, although occurring in Borneo and N. Celebes; one of them reaches Palawan. The strikingly Malay genus Amphidromus reaches Palawan, but no farther (1 sp.), while 2 species reach Mindanao, and one of these penetrates as far as Bohol and S. Leyte. Amongst the slugs, Mariaella occurs again only in the Seychelles, and Tennentia only in Ceylon.

Land and Fresh-water Mollusca of the Philippines

Streptaxis 1 Ennea 10 Mariaella 3 Tennentia 1 Helicarion 21 Vitrinopsis 5 Vitrinoidea 1 Rhysota 17 Trochonanina 2 Euplecta 28 Hemiplecta 11 Hemitrichia 15 Xesta 2 Macrochlamys 5 Microcystis 3 Lamprocystis 17 Bensonia 4 Vitriniconus 16 Sitala 2 Kaliella 8 Trochomorpha 21 Endodonta 1 Plectopylis 3 Plectotropis 1 Aulacospira 3 Pupisoma 1 Satsuma 2 Dorcasia 2 Chloritis 7 Obbina 19 Papuina 1 Phoenicobius 7 Cochlostyla 247 Amphidromus 2 Hapalus (?) 4 Hypselostoma 1 Pupa 4 Clausilia 1 Subulina 3 Prosopeas 2 Opeas 4 Geostilbia 1 Tornalellina 1 Succinea 3 Vaginula 2 Ancylus 1 Limnaea 3 Planorbis 3 Physa 2 Melania 50 Pirena 2 Bithynia 1 Vivipara 7 Ampullaria 5 Acmella 2 Diplommatina 41 Arinia 6 Pupina 5 Registoma 7 Hargreavesia 1 Callia 2 Pupinella 3 Helicomorpha 4 Coptochilus 1 Alycaeus 1 Leptopoma 42 Lagochilus 11 Cyclophorus 31 Ditropis 7 Cyathopoma 5 Cyclotus 19 Omphalotropis 3 Helicina 18 Georissa 3 Anodonta 1 Cyrena 3 Corbicula 7

Islands adjacent to the Philippines.--The Philippines are connected with Borneo by two distinct ridges or banks of elevation, which enclose between them the Soo-loo or Mindoro Sea. There can be little doubt that these ridges represent the ancient highway of transit, by which Indo-Malay species passed into the Philippines. The depth of the sea on either side is profound, ranging from an average of about 1000 fathoms west of Palawan to 2550 off the south-west coast of Mindanao.

It appears that the fauna of the Soo-loo ridge is definitely Philippine up to and including Bongao, Sibutu, and Bilatan, the last islands at the Bornean end of the ridge. On these are found two species of Cochlostyla and an Obbina.

The Palawan ridge may also be described as more or less Philippine throughout. One species of Cochlostyla occurs on Balabac, just north of Borneo, and two on Palawan, but these are perhaps counterbalanced by the definitely Indo-Malay Amphidromus and Opisthoporus (1 sp. each). At the northern end of the ridge, on Busuanga and Calamian, the Philippine element predominates.

Representatives of two remarkable groups of Helix (Camaena and Phoenicobius) occur along the Palawan ridge and in Mindoro. The Phoenicobius find their nearest allies in the curious small group known as Obba, from N. Celebes, the Camaena possibly in a type of Helix (Hadra) occurring in New Guinea and N.E. Australia. The only other Helix from the whole of the E. Indies which bears any resemblance to the Phoenicobius group is H. codonodes Pfr., which is peculiar to the Nicobars. A few forms assigned to Camaena also occur in Further India and Siam. It would appear possible, therefore, that these two isolated groups are a sort of survival of a fauna which perhaps had once a much more extended range.

(2) The =Chinese Sub-region=.--The Chinese Sub-region includes the whole of China from its southern frontier up to and including the basin of the Blue or Yang-tse River, together with the coast district, including Corea, perhaps as far north as Vladivostok, and the outlying islands of Hainan, Formosa, the Loo-Choo and Bonin groups, and Japan to the north of Niphon. It may be divided into two provinces, the Chinese and the Japanese.

(a) The fauna of the Chinese province proper bears, in many respects, strong marks of relationship to that of India and Siam. Thus Streptaxis, Helicarion, Macrochlamys, Kaliella, Sitala, Ariophanta, Rhysota, Hemiplecta, Diplommatina, Opisthoporus, Pterocyclus, Lagochilus, and Alycaeus all occur, especially in Southern China. The two points in which the sub-region bears special marks of individuality are Helix and Clausilia. The sub-genera of Helix which have their metropolis in China are Satsuma, Cathaica, Aegista, Acusta, Euhadra, Plectotropis, and Plectopylis. Sinistral forms (compare Fig. 213) are rather prevalent. In several cases--e.g. Trichia, Gonostoma, Fruticicola--there is a reappearance of forms which appear to belong to well-known European sub-genera. Clausilia here attains a kind of second centre of distribution, and is represented by its finest forms, which belong to several peculiar sub-genera. The carnivorous Mollusca are not abundant, and are represented by Rathouisia (a peculiar genus of naked slug), Ennea, and Streptaxis. In the western provinces Buliminus is abundant in several sub-genera, one of which appears to be the European Napaeus.

There is little which is striking in the operculates, which are most abundant in the south, and appear to be mainly derived from Indian and Siamese sources. The occurrence of Helicina (3 sp.), Omphalotropis (1), Leptopoma (2), and Realia (2), is evidence of some influence from the far East. Heudeia is a very remarkable and quite peculiar form of Helicina with internal plicae, perhaps akin to the Central American Ceres.

Fresh-water genera are exceedingly abundant, especially Melania, Unio, and Anodonta. The occurrence of Mycetopus (a South-American genus) is remarkable. There are several peculiar forms of fresh-water operculates, whose exact position is hardly yet assured.

Land and Fresh-water Mollusca of the Chinese Province

Rathouisia 1 Streptaxis 7 Ennea 12 Parmarion 2 Helicarion 15 Euplecta 3 Macrochlamys 19 Microcystina 2 Microcystis 7 Kaliella 16 Sitala 8 Ariophanta 1 Rhysota 5 Hemiplecta 1 Trochomorpha 2 Limax 1 Philomycus 1 Patula 2 Gonostoma 4 Metodontia 2 Vallonia 1 Plectotropis 9 Fruticicola 11 Satsuma 14 Trichia 10 Cathaica 22 Aegista 10 Armandia 3 Acusta 15 Obbina 1 Camaena 5 Euhadra 14 Plectopylis 19 Stegodera 6 Chloritis 1 Hel. Inc. sed. 39 Buliminus 21 Buliminopsis 3 Buliminidius 3 Napaeus 14 Rachis (?) 4 Pupa 10 Clausilia 102 Opeas 12 Euspiraxis 1 Subulina 5 Stenogyra (?) 12 Succinea 8 Vaginula 7 Limnaea 2 Planorbis 6 Melania 44 Paludomus 3 Bithynia 12 Lithoglyphus 3 Melantho (?) 1 Pachydrobia 1 Prososthenia 2 Stenothyra 2 Hydrobia 2 Mecongia 1 Oncomelania 9 Margaracya 1 Rivularia 4 Delavaya 1 Fenouillia 1 Vivipara 34 Diplommatina 20 Pupina 6 Alycaeus 23 Leptopoma 2 Lagochilus 10 Cyclophorus 18 Coelopoma 1 Pterocyclus 3 Opisthoporus 4 Cyclotus 10 Scabrina 4 Ptychopoma 12 Omphalotropis 1 Realia 2 Pseudopomatias 1 Helicina 3 Georissa 4 Heudeia 1 Cyclas 1 Corbicula 50 Unio 53 Monocondylaea 1 Anodonta 55 Mycetopus 12 Pseudodon 1 Dipsas 4

The island of Hainan, in the extreme south of the sub-region, has 40 species of Mollusca, 22 of which are peculiar, but there is no peculiar genus.

The Mollusca of Formosa, although in many cases specifically distinct, show close generic relationship with those of China. The characteristic Chinese groups of Helix and Clausilia occur, and there is still a considerable Indian element in several species of Streptaxis, Macrochlamys, Kaliella, and Alycaeus. The occurrence of two Amphidromus, a genus which, though Siamese, is not found in China or Hainan, is remarkable.

The peninsula of Corea must undoubtedly be included in the Chinese sub-region. It is true that the land operculates scarcely occur, but there are still a number of Clausilia, and several of the characteristic Chinese groups of Helix are reproduced. In some points Corea appears to show more affinity to Japan than to China, four of the Helices being specifically identical with those of Japan, but the peninsula is at present too little explored for any generalisations to be made as to its fauna in this respect.

(b) Japanese Province.--Kobelt distinguishes four groups of Mollusca inhabiting Japan (a) circumpolar species, actually occurring in Europe, Siberia, or N. America, or represented by nearly allied species (these of course do not belong to the Japanese province as such); (b) Indo-tropical species; (c) species which are Chinese or akin to Chinese; (d) peculiar species, a mixture of two forms, southern and northern, the latter being chiefly Hyalinia, Patula, and Fruticicola. Out of a total of 193 Japanese species, at least 164 are peculiar.

The Japanese Helices belong to sub-genera common to China (Plectotropis 8, Euhadra 21, Acusta 23?); but the Naninidae scarcely occur at all. The principal feature of the fauna is the development of Clausilia, which presents some extraordinarily fine forms. One slug (Philomycus) is identical with an Indian species. The operculates, which consist mainly of a few species each of Diplommatina, Cyclophorus, Pupinella, Pupina, Helicina, and Georissa, belong almost exclusively to the southern islands Kiu-siu, Sikoku, and southern Niphon. The three species usually reckoned as Japonia are probably forms of Lagochilus.

=C. The Australasian Region=

This region includes all the islands of the Pacific east of the Moluccas, and falls into three sub-regions--the Papuan, the Australian, and the Polynesian.

1. The =Papuan Sub-region= may be divided into--(a) the Papuan Province proper, which includes New Guinea, with the Aru Is. and Waigiou, the Admiralty Is., New Ireland, New Britain, and the d’Entrecasteaux and Louisiade Groups; (b) the Queensland Province, or the strip of N.E. Australia from C. York to the Clarence R. (about 29° S. lat.); (c) the Melanesian Province, which includes the New Hebrides, New Caledonia, with the Loyalty Is. and the Viti Is. The Solomons form a transition district between the Papuan and Melanesian provinces, abounding on the one hand in characteristic Papuan Helices, while on the other they form the north-western limit of Placostylus, the group especially characteristic of the Melanesian province.

(a) The Papuan Province.--The molluscan fauna of New Guinea is the richest and by far the most original of all the Australasian region. We find ourselves, almost in a moment, in a district full of new and peculiar forms. New Guinea may be regarded as the metropolis of the rich Helicidan fauna, which is also characteristic of the Moluccas to the west, of N. and N.E. Australia to the south and south-east, and of the Solomons and other groups to the north-east. Here abound species of Papuina and Insularia (the latter being quite peculiar), among which are found, if not the largest, certainly the most finished forms of all existing Helices. Chloritis (13 sp.), Planispira (5), and Cristigibba (9) are common with the Moluccas, while a tropical Australian element is shown in Pedinogyra (1) and Hadra (4). Very remarkable, too, is the occurrence of one species of Obbina and Rhysota, genera which culminate in the Philippines and here find their most eastward extension; while a single Corasia serves to form a link between the Corasia of the Philippines and those of the Solomon Is., if the latter are true Corasia.

We naturally find considerable traces of a Polynesian element, which appears to be principally characteristic of the eastern part of the island. Most noteworthy in this respect is the occurrence of Partula (3), Tornatellina (1), Charopa (1), Thalassia (3). As compared with the true Pulmonata, the operculates are feebly represented, and the great majority are of a markedly Polynesian type. Not a single Cyclophorus occurs; Lagochilus, Alycaeus, and all the tubed operculates, so marked a feature of the Indo-Malay fauna, are conspicuous by their absence, and the prevailing genera are Cyclotus, Helicina, and a number of sections of Pupina. Leptopoma, as in the Philippines, is strongly represented. Not that an Indo-Malay element is altogether absent. We still have Xesta (5), Hemiplecta (8), and even Sitala (2), but the great predominance of Helix seems to have barred the progress, for the greater part, of the Indian Naninidae.

The slugs appear to be represented by a solitary Vaginula. A single Perrieria is a very marked feature of union with Queensland, where the only other existing species (P. australis) occurs. The solitary Rhytida, so far the only representative of the carnivorous group of snails, emphasises this union still further. Little is known of the fresh-water fauna. Melania (28 sp.) is predominant, but on the whole the relations are Australian rather than Indo-Malay. Ampullaria is wanting, while a decisive point of similarity is the occurrence of Isidora (3 sp.), a genus entirely strange to the Oriental region, but markedly characteristic of the Australasian.

Land and Fresh-water Mollusca of New Guinea

Rhytida 1 Helicarion 2 Rhysota 1 Hemiplecta 11 Xesta 2 Microcystis 3 Microcystina 2 Sitala 2 Oxytes (?) 2 Conulus 1 Trochomorpha 8 Nanina (?) 3 Charopa 1 Thalassia 3 Ochthephila(?) 1 Chloritis 13 Planispira 5 Cristigibba 9 Insularia 17 Obbina 1 Albersia 3 Hadra 4 Pedinogyra 1 Papuina 35 Corasia (?) 1 Bulimus (?) 1 Calycia 4 Partula 3 Pupa 1 Stenogyra 1 Tornatellina 1 Perrieria 1 Succinea 1 Vaginula 1 Limnaea 2 Isidora 3 Melania 28 Faunus 1 Vivipara 4 Diplommatina 1 Pupina 4 Pupinella 3 Omphalotropis 2 Bellardiella 2 Leptopoma 16 Cyclotus 5 Cyclotropis 5 Helicina 15 Unio 4 Cyrena 3 Corbicula 1 Batissa 8

Waigiou is practically a part of New Guinea. Twelve genera and twenty species of Mollusca are known, eight of the latter being peculiar. The occurrence of Papuina, Insularia, and Calycia sufficiently attest its Papuan relationship. Two species each of Albersia, Chloritis, and Planispira occur.[372]

The Aru Is. are, as we should expect from their position, and particularly from the configuration of the adjacent sea bottom (see map), markedly Papuan. At the same time they show unmistakable signs of long-continued separation from the parent island, for of their 36 land Mollusca 15, and of their 20 fresh-water Mollusca 9 are peculiar. The Papuan element consists in the presence of Papuina, Albersia, and Cristigibba. Moluccan influence is not absent, for the three Helicina, the Albersia, and one Cyclotus are all Moluccan species. The fresh-water fauna appears to be a mixture of varied elements. The single Segmentina is common to India, the Glaucomya to Malacca and the Philippines, while the single Batissa is also found in New Zealand.

Land and Fresh-water Mollusca of the Aru Islands

Xesta 4 Microcystis 1 Hyalinia(?) 1 Trochomorpha 1 Patula 1 Eulota 1 Chloritis 5 Cristigibba 2 Albersia 1 Papuina 4 Pupa 2 Stenogyra 2 Planorbis 1 Segmentina 1 Melania 14 Leptopoma 3 Moussonia 1 Realia 1 Cyclotus 3 Helicina 3 Cyrena 2 Glaucomya 1 Batissa 1

The Louisiades, the d’Entrecasteaux, and Trobriand Is., and Woodlark I., are closely related to New Guinea, containing no peculiar genera. Each group, however, contains a considerable proportion of peculiar species, an indication that their separation from New Guinea dates from a very distant period. From the Louisiades are known 34 species in all, 22 of which are peculiar.

The fauna of the Admiralty Is., of New Hanover, and New Ireland is markedly Papuan, without any especial feature of distinction. The Admiralty Is. contain 15 sp. Papuina, 7 Chloritis, 1 Planispira, and 1 Corasia. A single Janella shows relationship with the New Hebrides and with New Zealand. In New Ireland Planispira (which is specially characteristic of W. New Guinea and the Moluccas) has disappeared, but there are 7 Papuina and 6 Chloritis. The essentially Polynesian Partula is present in both groups.

The prominent feature of the Mollusca of the Solomon Is. is the extraordinary development of Papuina, which here culminates in a profusion of species and singularity of form. The genus is arboreal, crawling on the branches and attaching itself to the leaves of trees and underwood. Of the 140 land Pulmonata known from the group, no less than 50, or 36 per cent, are Papuina. Ten species of Corasia occur, but whether the shells so identified are generically identical with those of the Philippines, is not satisfactorily determined. Trochomorpha, with 22 species, here attains its maximum. Chloritis begins to fail, but still has 3 species. Indo-Malay influence still appears, though feebly, in Hemiplecta (3), Xesta (1), and possibly even Macrochlamys (1). The Rhytida, the 3 Hadra, and possibly the Paryphanta represent the Australian element. The growing numbers of Partula (13), the small and inconspicuous land operculates (only 22 in all, with Helicina very prominent), and the almost complete absence of fresh-water bivalves, show signs of strong Polynesian affinities. An especial link with the New Hebrides, New Caledonia, and the Viti Is. is the occurrence of Placostylus (16 sp.). It is very remarkable that this genus should occur in the Solomon Is. and not in New Ireland. The occurrence of Streptaxis, if authentic, is very noteworthy, the nearest species being from the Philippines.

Land and Fresh-water Mollusca of the Solomon Islands

Streptaxis (?) 1 Rhytida 1 Paryphanta (?) 1 Helicarion 2 Xesta 1 Macrochlamys 1 Hemiplecta 3 Microcystis 2 Trochomorpha 22 Nanina (?) 2 Patula 1 Thalassia 2 Chloritis 3 Philina 2 Hadra 3 Papuina 50 Merope 1 Corasia (?) 10 Placostylus 16 Partula 13 Succinea 1 Melania 18 Diplommatina 2 Pupina 4 Leptopoma 4 Omphalotropis 2 Cyclotus 1 Cyclotropis 2 Helicina 7 Unio 1

(b) The Queensland Province.--The strip of coast-line from Cape York to the Clarence R. stands apart from the rest of Australia, and is closely connected with New Guinea. There can be little doubt that it has been colonised from the latter country, since an elevation of even 10 fathoms would create (see map) a wide bridge between the two. Many of the genera are quite strange to the rest of Australia. Land operculates are abundant, and of a Papuan type. Several of the characteristic Papuan genera of Helix (Papuina, Chloritis, Planispira) occur, while Hadra attains its maximum. Panda, Pedinogyra, and Thersites are three remarkable groups in a rich Helix fauna. Parmacochlea is a peculiar form akin to Helicarion. The carnivorous Mollusca are represented by Rhytida, Diplomphalus (New Caledonia), and Elaea. One species of Janella, a slug peculiar to this region, occurs. The predominant fresh-water genus is Bulinus (Isidora). Ampullaria and Anodonta are entirely absent from Australia and New Zealand.

Land Mollusca of the Queensland Province

Diplomphalus 1 Rhytida 10 Elaea 1 Parmacochlea 1 Helicarion 7 Nanina 3 Hyalinia 10 Thalassia 4 Charopa 5 Patula (?) 4 Macrocyclis (?) 1 Helicella 10 Planispira 8 Hadra 51 Chloritis 5 Pedinogyra 1 Thersites 1 Papuina 6 Panda 2 Helix (inc. sed.) 6 Bulimus (?) 1 Stenogyra 1 Tornatellina 4 Pupa 3 Vertigo 4 Perrieria 1 Succinea 3 Vaginula 1 Janella 1 Georissa 1 Pupina 16 Hedleya 1 Callia 1 Diplommatina 3 Ditropis 2 Dermatocera 1 Helicina 8

(c) The Melanesian Province includes those islands on which the remarkable group Placostylus occurs, the metropolis of whose distribution is New Caledonia. These islands are very possibly the remains of what was once a much wider extent of land. A single species of Placostylus occurs both on Lord Howe’s I. and in the North I. of New Zealand, but this fact, while highly interesting as indicating a possible former extension of land in a south-easterly direction, is hardly sufficient to bring these islands within the province as now limited. The Solomon Is., although containing Placostylus as far to the west as Faro I., form, as has been already stated, a transitional district to the Papuan province.

New Caledonia.--The chief features of the Mollusca are the remarkable development of the helicoid carnivorous genera Rhytida (30 sp.) and Diplomphalus (13 sp.), and of Placostylus (45 sp.). There is a stray Papuina, and a peculiar form Pseudopartula, but Helix has almost entirely disappeared. Polynesian influence is represented by Microcystis (3 sp.), the so-called Patula (13 sp., many of which are probably Charopa), Tornatellina (2 sp.), and Helicina (20 sp.). Partula does not reach so far south, but there are two species of Janella. The recurrence of Melanopsis (19 sp.), absent from the whole Oriental region, is curious, and forms another link with New Zealand. The curious sinistral Limnaea (Isidora), common with Australia and New Zealand, is abundant.

The New Hebrides link New Caledonia and the Solomons by their possession of the typical heavy Placostylus (5 sp.) of the former, and the lighter and more elegant Charis (2 sp.) of the latter. There are 4 Papuina, and Partula is abundant (18 sp.), but there is no evidence at present that the carnivorous genera or the Melanopsis and Isidora of New Caledonia occur.

The Fiji Is., by the possession of 14 Placostylus of the Charis section, which is entirely absent from the adjacent Tonga group, form the eastern limit of the province. There appears to be only a single Partula, but the Polynesian element, especially as seen in Navicella (8 sp.), Neritina (20 sp.), Helicina (11 sp.), and Omphalotropis (11 sp.), is very strong. The Microcystis (9 sp.) and Trochomorpha (14 sp.) are also of a Polynesian type.

(2) The =Australian Sub-region= includes the whole of Australia (with the exception of the Queensland province) and Tasmania, with New Zealand and the off-lying islands. The fauna, from the prevalence of desert, is scanty, especially in genera. Land operculates are almost entirely wanting. Limax is not indigenous, though several species have become naturalised. The bulk of the fresh-water species belong to Isidora, and it is doubtful whether Physa occurs at all. Unio has a few species, and also Vivipara, but neither Anodonta nor Ampullaria occur. There are a few Melania and Neritina.

Tropical South Australia.--The Mollusca are scanty, and occur chiefly in the neighbourhood of the rivers, the soil being arid, with no shelter either of trees or rocks. Fresh-water species predominate, and the rich land fauna of Queensland is totally wanting. There are no land operculates, 6 Hadra, 1 Bulimus (?), 1 Stenogyra.

West Australia.--Owing to the deserts which bound it, the Mollusca are very isolated, only one species being common with N., S., and E. Australia. The chief characteristics are Liparus, a form intermediate between Helix and Bulimus, and, among the Helices, the group Rhagada. There are no slugs, no carnivorous snails, and only three land operculates.

Land Mollusca of West Australia

Lamprocystis 1 Hyalinia 1 Patula 7 Chloritis 2 Gonostoma 2 Trachia 3 Xerophila 1 Rhagada 8 Hadra 5 Liparus 10 Pupa 4 Succinea 3 Cyclophorus 2 Helicina 1

In Eastern and Southern Australia (New South Wales, Victoria, and South Australia) the tropical element, so abundant in Queensland, almost entirely disappears, the last operculate (a Helicina) only reaching Port Macquarie, though several species of Helicarion occur in the extreme south. Hadra is still abundant in New South Wales (18 sp.) and S. Australia (10 sp.), but becomes scarce in Victoria (2 sp.); New South Wales has also one Panda and two Thersites. Cystopelta is common with Tasmania, and one of the Janellidae (Aneitea) with Queensland. The carnivorous snails are represented by Rhytida. Caryodes, a bulimoid group perhaps akin to Liparus, is common with Tasmania only.

Tasmania.--About 80 species of land Mollusca are known, not more than 10 being common with Australia. No land operculates occur; Endodonta and Charopa are rare, and Hadra has entirely disappeared, but Pupa and Succinea occur. Carnivorous genera are represented by Paryphanta, Rhytida, and Rhenea. Anoglypta is a peculiar section of Helix, while Caryodes, Cystopelta, and Helicarion are common with Australia. Among the fresh-water Mollusca are a Gundlachia (see p. 345), and some forms of Amnicola or Hydrobia, one of which (Potamopyrgus) is common only with New Zealand.[373]

The Neozealanian Province.--The Mollusca of New Zealand, with the Kermadec, Chatham, and Auckland Is., are remarkably isolated. Such genera as Nanina, Partula, Pupa, Stenogyra, Succinea, Vaginula, Truncatella, Helicina, and Navicella, which might have been expected to occur, are entirely absent. The bulk of the land Mollusca are small and obscure forms, perhaps remains of a very early type, and appear to belong to the Zonitidae, neither Patula nor Helix occurring at all. The carnivorous forms are represented by Schizoglossa, a peculiar genus akin to Daudebardia, by Paryphanta, an extraordinary group of large shells with a thick leathery epidermis, and by Rhytida and Rhenea. In spite of its extreme isolation, the general relations of the fauna are partly with New Caledonia, partly with E. Australia. The occurrence of Placostylus has already been mentioned (p. 323), and three species of Janella, a genus which also occurs in Queensland and New Caledonia, indicate the same affinity. Otoconcha is peculiar. The fresh-water Mollusca, besides the Isidora characteristic of the sub-region, are partly related to New Caledonia through the occurrence of Melanopsis, partly to Tasmania through Potamopyrgus, while the peculiar Latia is possibly akin to Gundlachia (Tasmania). The land operculates number only 5 genera and 14 species in all, excluding a doubtful Diplommatina.[374]

Land and Fresh-water Mollusca of the Neozealanian Province

Schizoglossa 1 Paryphanta 5 Rhytida 6 Rhenea 2 Helicarion 1 Otoconcha 1 Microcystis 1 Trochonanina 1 Phacussa 3 Thalassohelix 5 Gerontia 2 Allodiscus 10 Pyrrha 1 Therasia 7 Phenacohelix 3 Suteria 1 Flammulina 13 Laoma 23 Endodonta 10 Charopa 28 Placostylus 1 Carthaea 1 Tornatellina 1 Janella 3 Latia 2 Ancylus 2 Limnaea 5 Amphipeplea 2 Planorbis 1 Isidora 7 Melanopsis 2 Potamopyrgus 4 Paxillus 1 Lagochilus 7 Omphalotropis 1 Realia 4 Hydrocena 1 Unio 9 Sphaerium 1 Pisidium 2

Lord Howe’s I. is remarkable as containing a Placostylus, which thus links the island with this province. The remainder of the fauna is Polynesian, with the exception of a species (common to the Fijis) of Parmella, a slug akin to Helicarion, Parmacochlea, and Cystopelta.

(3) The =Polynesian Sub-region= includes all the island groups of the central and southern Pacific (except those classified in the Papuan and Australian sub-regions), from the Pelews and Carolines in the west to the Marquesas and Paumotus in the east, and from the Tonga group in the south to the Sandwich Is. in the north. It may be subdivided into (a) the Polynesian province proper, and (b) the Hawaiian province, which includes the Sandwich Is. only.

(a) The general features of the Polynesian province are very similar throughout, although the Mollusca of each island group are in the main peculiar. The species are mostly small and obscure. Helix scarcely occurs, its place being taken by small Zonitidae (Microcystis, Charopa, Trochomorpha, etc.), and by groups of so-called Patula (Endodonta, Pitys, etc.), the exact position of which is not yet settled. Libera, remarkable for its method of ovipositing (p. 128), is peculiar to the Society and Hervey Is.; Partula is almost universal, attaining its maximum (40 sp.) in the Society Is.; Tornatellina, Pupa, and Vertigo occur throughout.

The land operculates consist chiefly of Omphalotropis, Pupina, Realia, and Helicina. Diplommatina and Palaina are abundant on the Pelews, and a Moussonia occurs in the Samoa Is. Ostodes, a small form of Cyclophorus, is found in some of the southern groups. The fresh-water operculates are Melania, Neritina (including Clithon, a sub-genus furnished with spines), and Navicella; there are no Unionidae, while fresh-water Pulmonata are very scarce.

(b) The land Mollusca of the Hawaiian province are distinguished by the possession of four entirely peculiar genera--Achatinella, Leptachatina, Carelia, and Auriculella. More than 300 of the two former genera have been described, every mountain valley of some of the islands having its own peculiar species. The destruction of the indigenous herbage by goats is rapidly extinguishing many forms. Partula, and the small land operculates, so characteristic of the other groups, are, with the exception of Helicina, entirely wanting. The occurrence of one of the Merope group of Helix (Solomon Is.) is remarkable, and there is a rich development of Succinea. “Patula,” Microcystis, Tornatellina, and the other small Polynesian land Pulmonata are well represented. The presence of Isidora, absent from the central Pacific groups, is remarkable, and Erinna is a peculiar genus belonging to the Limnaeidae.

Spotted a typo or a problem in this chapter? Tell us

Chapter XI

GEOGRAPHICAL DISTRIBUTION OF LAND MOLLUSCA (continued)--THE ETHIOPIAN, NEARCTIC, AND NEOTROPICAL REGIONS

=D. The Ethiopian Region=

The Ethiopian region includes the whole of Africa south of the Great Desert, and Southern Arabia, together with the outlying islands, excepting those of the Atlantidean province (p. 297).

Regarded as a whole, the Ethiopian is poorest in land Mollusca of all the tropical regions. And yet its characteristics are very remarkable. The entire Achatina group is peculiar, and takes, especially in W. Africa, some curious forms (Columna, Perideris, Pseudachatina). Carnivorous Mollusca (Ennea, Gibbus, etc.) are highly developed, especially in the south and east, the largest known helicoid form (Aerope) being from Natal. In the possession of these types of the Agnatha, Africa is more closely related to the Australasian than to the Oriental region. The true Cyclostoma are entirely peculiar to the region, but are absent from West Africa.

Fresh-water Mollusca are abundant and characteristic, especially in and near the Great Lakes. Lanistes, Cleopatra, and Meladomus, among the operculates, together with Mutela and Aetheria (Unionidae), Galatea and Fischeria (Cyrenidae), are peculiar.

In its negative, as well as its positive features, the Ethiopian region is markedly isolated. Helicidae and Naninidae are equally deficient, the former, indeed, attaining some numerical predominance in the extreme south, but the species are nearly all insignificant in size and colouring. It is only in Madagascar that Helix asserts itself. Arion, Limax, Hyalinia, Clausilia, and a number of other genera abundant along the Mediterranean, are either altogether absent, or are very scantily represented. Land operculates, so characteristic of other tropical countries, are almost entirely wanting. If we disregard the Malagasy sub-region, there are scarcely forty species of land operculates on the whole African continent.

The Ethiopian region may be divided into three sub-regions: (1) the Central African; (2) the South African; (3) the Malagasy.

(1) =The Central African Sub-region= is bounded on the north by the Great Desert, on the east and west by the ocean, and on the south by a line roughly drawn between the mouth of the Orange River and Delagoa Bay; it also includes S. Arabia. No natural features exist which tend to break up this vast district into areas of independent zoological development. The absence of long and lofty mountain ranges, the enormous size of the great river basins, and the general uniformity of climate, equalise the conditions of life throughout. It will be convenient to break the sub-region up into provinces, but in most cases no precise line of demarcation can be laid down.

(a) The Senegambian Province may be regarded as extending from the mouth of the Senegal River to Cape Palmas. Only 8 genera of land Mollusca are known, including 4 Limicolaria and 3 Thapsia, with 1 small Cyclophorus. Fresh-water genera are abundant, and include most of the characteristic Ethiopian forms.

(b) The West African Province extends from Cape Palmas to the mouth of the Congo, and is rich in Mollusca. The great Achatina, largest of land snails, whose shell sometimes attains a length of 6½ in., Limicolaria, Perideris, and Pseudachatina are the characteristic forms. The Agnatha are represented by Ennea, Streptaxis, and Streptostele. Rachis and Pachnodus, sub-genera of Buliminus, occur also on the east coast. A special feature is the development of several peculiar slug-like genera, e.g. Oopelta, perhaps a form of Arion; Estria, a slug with an external shell, akin to Parmacella; and Aspidelus, a form intermediate between Helicarion and Limax. Claviger, a handsome group akin to Cerithium, is peculiar to the estuaries of West African rivers.

About sixteen species are known from the Cameroons District, but no peculiar genera occur. The French Congo District has not yet been well explored. Tomostele, a genus allied to Streptostele, is peculiar, and Pseudachatina attains its maximum.

St. Thomas and Princes Is., in the Gulf of Guinea, are well known. Princes I. has 22 species, 14 peculiar, and 2 common to St. Thomas only, one of the latter being the great sinistral Achatina bicarinata Chem. The remarkable genus Columna (Fig. 217) is peculiar, and Streptostele (4 sp.) attains its maximum. Peculiar to St. Thomas are Pyrgina, a turreted form of Stenogyra; Thyrophorella, a sinistral form of Zonites; and Atopocochlis, a large bulimoid shell, whose true relationships are not yet known. Homorus, a group of Achatina with an elongated spire, occurring also in the Angola District and on the east coast, has 4 species. No fresh-water species have as yet been discovered in either of the islands.

The Angola and Benguela District, extending from the Congo to the Cunene R., probably belongs to the West African Sub-region, but until its fauna is better known it is advisable to consider it apart. Achatina continues abundant, but the other characteristic West African forms (Pseudachatina, Streptostele, Perideris) diminish or are absent altogether. No Helix and only 1 Cyclophorus occur.

Ovampo, Damara, and Great Namaqualand, lying between the Cumene and Orange rivers, seem to form a transition district between the West and South African faunas. Helix reappears, while the characteristic West African genera are almost entirely wanting.

(c) The East African Province extends from about Delagoa Bay to the Abyssinian shores of the Red Sea. In general out-line the province consists of a flat marshy district, extending inland for many miles from the sea; this is succeeded by rising ground, which eventually becomes a high table-land, often desolate and arid, whose line of slope lies parallel to the trend of the coast. The Mollusca are little known, and have only been studied in isolated districts, usually from the discoveries of exploring expeditions.

The Mozambique District, from Delagoa Bay to Cape Delgado, includes no genus which does not occur on the west coast, except Cyclostoma (2 sp.). Trochonanina (4 sp.), Urocyclus, a characteristic African slug (2 sp.), Rachis (6 sp.), Pachnodus (2 sp.), and Achatina (5 sp.), are the principal groups.

The Zanzibar District, from Cape Delgado to the Somali country, has the same general features. Meladomus, a large sinistral Ampullaria, is characteristic, while Cyclostoma (5 sp.) becomes more abundant. Helix is still absent, but the carnivorous forms (Streptaxis 2 sp., Ennea 7 sp.) are rather numerous.

The Somali District is characterised by operculate groups of the Otopoma type (Georgia, Rochebrunia, Revoilia) whose generic value is rather doubtful. Petraeus, in an Arabian type, supplants Rachis and Pachnodus. Achatina is nearly wanting, but Limicolaria has 9 species. A few Helix, said to be of the Pisana group, occur.

The District between the Great Lakes and the coast region is fairly well known through recent explorations, especially those associated with Emin Pasha. Streptaxis (6 sp.) and Ennea (24 sp.) are numerous, Helix is wanting, and the Naninidae are represented by Trochonanina (7 sp.), and other forms at present grouped under Nanina or Hyalinia. On the high ground Buliminus, Cerastus, and Hapalus replace, to some extent, the Achatina and Limicolaria of the marshy plains. Land operculates (Cyclophorus 1, Cyclostoma 8) are more numerous; among fresh-water genera we have Lanistes (5 sp.), Cleopatra (3 sp.), Meladomus (1 sp.), and Leroya, a sinistral form with the facies of a Littorina. The characteristic African bivalves (Mutela, Spatha, etc.) are few in number.

(d) Province of the Great Lakes.--The Mollusca of the four great lakes of Eastern Central Africa--Lakes Albert Nyanza (Luta Nzige, 2720 ft.), Victoria Nyanza (Oukéréwé, 3700 ft.), Nyassa (1520 ft.), and Tanganyika (2800 ft.)--are well known, and supply an interesting problem in distribution. Those of the three first mentioned lakes differ in no way from the rest of tropical Africa, but the Mollusca of Tanganyika include, in addition to the ordinary African element, a number of peculiar operculate genera, belonging principally to the Melaniidae and Hydrobiidae. Several of these possess a solidity of form and compactness of structure which is unusual in fresh-water genera, and has led to the belief, among some authorities, that they are the direct descendants of marine species, and that Tanganyika represents an ancient marine area. This view appears untenable. The Victoria Nyanza and Nyassa are part of the same system as Tanganyika, and it is not easy to see how, if Tanganyika were once an arm of the sea, they were not equally so, especially as they are several hundred miles nearer the Indian Ocean as at present defined. Nor, as will be seen from the figures given above, is there anything in the altitudes which would make us expect anything exceptional in Tanganyika. The similar case of L. Baikal must be compared (p. 290), where again a number of specialised forms of Hydrobia occur.

Of the genera concerned, Paramelania and Nassopsis are forms of Melaniidae; Tiphobia (Fig. 219), which is allied to Paludomus, is a compact shell with angulated spinose whorls; Lacunopsis, Ponsonbya, Limnotrochus, and Tanganyicia are probably forms of Lithoglyphus, some, as their names denote, being of decidedly marine facies; Syrnolopsis and Turbonilla (?) look like Pyramidellidae, Horea and Reymondia like Rissoina; Bourguignatia appears to belong to Vivipara, with which has now been merged the genus Neothauma. Recently discovered forms from the adjacent L. Mweru are evidently of kindred origin.

(e) The Afro-Arabian Province includes Abyssinia, with S. Arabia, the African shores of the Gulf of Aden, and Socotra. The province contains a singular mixture of types. The high ground of Abyssinia stands like a lofty European island in the midst of a tropical plain, with Palaearctic genera flourishing like hardy northern plants on a mountain in low latitudes. Helix, Vitrina, and Pupa abound, with a few Clausilia and even a Limax. On the lower levels occur Limicolaria (3 sp.), Subulina (7 sp.), Helicarion, and Homorus, but land operculates are entirely wanting. Characteristic of the province as a whole are various forms of Buliminus, which in Socotra are represented by two peculiar sub-genera, Achatinelloides and Passamaiella. In S. Arabia the mixture of types produces curious results: the Helix, Clausilia, and Vitrina being Palaearctic, the Limicolaria and all the operculates Ethiopian, while the single Trochomorpha is Indian. Indian influence, indeed, comes out unmistakably throughout the province. Thus in Socotra there are two Cyclotopsis, in Abyssinia two Africarion (closely related to the Indian Girasia), two Microcystis, and a Glessula, and in the Scioa district there is a Sitala. The fresh-water Mollusca of Socotra are Indian forms.

(2) =The South African Sub-region.=--The principal characteristic of the Mollusca of S. Africa is the occurrence of numerous small species of Helicidae, belonging chiefly to the groups Pella, Phasis, Dorcasia, and Sculptaria, all of which are practically peculiar. Carnivorous genera are also prominent, Ennea here attaining its maximum. Rhytida (to which several species still regarded as Pella belong) is common only to the S. Pacific and Australasia, and forms, with Isidora among the fresh-water pulmonates, a remarkable link of connexion. Aerope, the largest of all helicoid carnivorous genera, and Chlamydephorus, a carnivorous slug with an internal shell, are peculiar. Achatina is still abundant, but Limicolaria is wanting. Livinhacea, a form with a continuous peristome, perhaps akin to Bulimus; Apera, a form of slug; and Coeliaxis, a genus perhaps akin to the Papuan and Queensland Perrieria, are all peculiar. The land operculates, which are not numerous, are of the East African type.

Land Mollusca of the S. African Sub-region

Chlamydephorus 1 Ennea 31 Aerope 5 Rhytida 3 Helicarion 3 Trochonanina 1 Trochozonites 1 Limax 1 Apera 1 Vitrina 7 Nanina 6 Conulus 2 Patula 2 Pella 44 Dorcasia 8 Phasis 1 Sculptaria 2 Helix (inc. sed.) 4 Rachis 1 Pachnodus 3 Buliminus (?) 4 Pupa 20 Vertigo 2 Achatina 18 Livinhacea 1 Stenogyra 4 Coeliaxis 1 Succinea 3 Vaginula 2 Cyclophorus 1 Cyclostoma 7 Cyclotus (?) 1 Blanfordia 1

St. Helena.--The Molluscan fauna of St. Helena is perhaps the most puzzling, as regards its geographical affinities, of any in the world. It consists of 29 peculiar species of land Mollusca (fresh-water species being unknown), 19 of which are recently extinct, partly owing to the destruction of the forest, but are found in considerable abundance in a state of good preservation.[375] The genera are--

Hyalinia 1 Patula 4 (3 extinct) Endodonta 10 (7 extinct) Bulimulus 7 (5 extinct) Pachyotus 1 (extinct) Tomigerus (?) 1 (extinct) Pupa 2 (extinct) Succinea 3

The 5 genera which concentrate our attention are Patula, Endodonta, Pachyotus (Fig. 222), Tomigerus, and Bulimulus, all of which appear utterly strange to an oceanic island in the middle of the S. Atlantic. Patula and Endodonta are essentially Polynesian forms, occurring abundantly on all the island groups in the Central Pacific. Pachyotus, Tomigerus (assuming its correct identification), and Bulimulus are all S. American forms, the two former being especially characteristic of Brazil. How this mixture of genera now confined to regions so widely distant, not only from St. Helena itself, but from one another, became associated here, is a problem obviously not easy of solution. The fauna is probably a remnant of a very ancient type, possibly at one time much more widely distributed. Endodonta (an essentially insular form, like Omphalotropis) actually occurs on Fernando Noronha, off the Brazil coast, and we shall see how an Indian and even a Polynesian element is present off the eastern coasts of Africa.

Ascension I.--One indigenous species, a so-called Limax, is all that has ever been discovered.

(3) =The Malagasy Sub-region= includes Madagascar with its attendant satellites Bourbon, Mauritius, and Rodriguez, and the Seychelles and Comoro groups. No land Mollusca are known from the Amirantes, the Chagos, or from Aldabra. The special characteristics of the sub-region are the great development of the carnivorous land Mollusca (Ennea, Gibbus), the occurrence of a considerable number of true Helicidae of great size and beauty, and the prominence of the genus Cyclostoma.

(a) The Madagascan Province.--The land Mollusca of Madagascar, although as yet imperfectly known, possess a striking individuality. Two of the chief characteristics of the Ethiopian region are the paucity of its land operculate and of its Helix fauna; Madagascar is especially distinguished by the rich development of both these groups. For size, colouring, and beauty of shape, the Helicidae of the two sub-genera Ampelita and Helicophanta rival, if they do not surpass, any in the world. They are quite peculiar to this sub-region, not a trace of them occurring on the Mascarenes, Seychelles, or even on the Comoros. Helicophanta is distinguished by the enormous size of its embryonic shell, which persists in the adult (Fig. 223), and in this respect the group appears to be related to Acavus (Ceylon, Fig. 204) and Panda (N.E. Australia). As is usual when Helix is well developed, Nanina (about 12 sp.) is proportionately scanty.

The African Bulimini (Pachnodus and Rachis) are represented by two species, but Achatina, so abundant on the mainland, is scarce. Two other groups of Buliminus, Leucotaenia and Clavator, are peculiar. The presence of a single Kaliella, specifically identical with a common Indian form, is very remarkable.

Cyclostoma proper, of which Madagascar is the metropolis, is richly developed (54 sp.). Many of the species are of great size and of striking beauty of ornamentation. Unlike its Helicidae, this genus is not restricted to Madagascar; several species occur on the mainland, 6 on the Comoros, one on the Seychelles, and 16 in Mauritius. The sub-genera Acroptychia and Hainesia are peculiar.

The fresh-water Mollusca of Madagascar contain further traces of Indian relationship. Thus we find two species of Paludomus, a genus whose metropolis is Ceylon, India, and Further India, and which is barely represented on the Seychelles and in the Somali district. Melanatria, which is peculiar to Madagascar, has its nearest affinities in the Cingalese and East Indian faunas. Several of the Melania and the two Bithynia are of a type entirely wanting in Africa, but common in the Indo-Malay sub-region. Not a single one of the characteristic African fresh-water bivalves (Mutela, Spatha, Aetheria, Galatea, etc.) has been found in Madagascar. On the other hand, certain African Gasteropoda, such as Cleopatra and Isidora, occur, indicating, in common with the land Mollusca, that an ultimate land connexion with Africa must have taken place, but at an immeasurably remote period.

Land and Fresh-water Mollusca of Madagascar

Ennea 9 Urocyclus 2 Helicarion (?) 1 Macrocyclis (?) 1 Kaliella 1 Nanina (inc. sed.) 9 Ampelita 35 Helicophanta 17 Pachnodus 2 Rachis 2 Leucotaenia 2 Clavator 2 Achatina 3 Opeas 2 Subulina 3 Vaginula 4 Limnea 2 Planorbis 3 Isidora 3 Melania 7 Melanatria 4 Paludomus 2 Vivipara 1 Bithynia 2 Cleopatra 2 Ampullaria 6 Cyclophorus 2 Cyclotus (?) 1 Cyclostoma 54 Otopoma 5 Lithidion 1 Acroptychia 3 Hainesia 3 Unio 1 Corbicula 2 Sphaerium 1 Pisidium 1

The Comoro Islands.--This isolated group possesses about 100 species, almost all of which are peculiar. The principal feature is the rich development of Ennea (30 sp.). On the whole the group shows more relationship to Madagascar than to the mainland. Thus we have six species of true Cyclostoma, and only one Achatina, while among the fresh-water genera is Septaria, which is characteristic of the whole Malagasy Sub-region, but is absent from the mainland. The Helicidae are all of insignificant size. Peculiar to the group is the remarkable genus Cyclosurus (Fig. 152, p. 247).

(b) The Mascarene Province (Mauritius, Bourbon, Rodriguez, and the Seychelles).--The percentage of peculiar species, which is very high, can only be paralleled in the case of some of the West Indian islands, and sufficiently attests the extreme isolation of the group from Madagascar. We have--

Fresh-water Peculiar to Total sp. Land sp. sp. Peculiar group

Mauritius 113 104 9 78 102 (90 p.c.) Bourbon 45 40 5 19 38 (84 p.c.) Rodriguez 23 19 4 15 21 (95 p.c.) Seychelles 34 27 7 24 30 (90 p.c.)

The Mollusca of the group exhibit three distinct elements, the Indigenous, the Madagascan, and the Indian and Australasian.

The genus Pachystyla (Naninidae) is quite peculiar, forming the main portion of the land snails proper. It attains its maximum in Mauritius (17 sp.), with 5 sp. in Bourbon and one sub-fossil sp. in Rodriguez, while in the Seychelles it is absent. But the principal feature of the Mascarene group is the extraordinary development of the carnivorous genus Gibbus, which has 27 sp. in Mauritius, 8 in Bourbon, 4 in Rodriguez; in the Seychelles, it is replaced by Edentulina and Streptostele. The principal link with Madagascar is found in a part of the operculate land fauna. Cyclostoma is present (with Otopoma) in several fine living forms, and the number of sub-fossil species is a clear indication that this group was, not long ago, much more abundant, for of the 16 Cyclostoma known from Mauritius 10 are sub-fossil. The operculates form a decided feature of the land fauna; thus in Mauritius there are 32 species, or more than 28 per cent of the whole.

Indian and Australasian affinities are unmistakably present. Thus Omphalotropis, a genus characteristic of small islands, is profusely represented, but it does not occur in Madagascar or Africa. Two Helicina (Mauritius and Seychelles) and a single Leptopoma (possibly a Leptopomoides) are also of eastern relationship. Cyclotopsis, Cyathopoma, and Geostilbia are markedly Indian genera. Microcystis, Patula, and Tornatellina are Polynesian. Hyalimax--and this is a very striking fact--occurs nowhere else but in the Andamans and Nicobars, and on the Aracan coast. The nearest relation to the Seychelles Mariaella appears to be the Cingalese Tennentia. Not a single representative of these eleven genera has been found even in Madagascar.

The fresh-water Mollusca (omitting the Neritidae) are: Mauritius 9 species, Bourbon 5, Rodriguez 4, Seychelles 6, with only 15 species in all. The one Planorbis and the Vivipara, the Paludomus and two of the Melania are of Indian types. The Lantzia (peculiar to Bourbon) is probably allied to the Indian Camptonyx. Owing to the paucity of permanent streams, no fresh-water bivalves occur. Among the Neritidae is a single Septaria, a genus which, though occurring in Madagascar, is entirely strange to Africa, and is abundant in the Oriental and Australasian regions.

It would seem probable that when the closer connexion which at one time undoubtedly existed between India and Eastern Africa began to be less continuous,[376] the Mascarene group was first severed from what ultimately became Madagascar, while the Seychelles, and perhaps the Comoros, still continued united to it. The Comoros, which lack the great Helices, separated off from Madagascar first, while the Seychelles continued in more or less direct union with that island sufficiently long to receive the progenitors of Stylodonta (a peculiar group of Helix), but became disunited at an exceedingly remote period.

=E. The Nearctic Region=

The southern boundary of this region may be regarded as roughly corresponding to that of the United States, i.e. Lower California and Mexico are excluded. The southern portion of Florida belongs to the Antillean sub-region.

The principal characteristic of the Nearctic Region is the remarkable poverty of its land Mollusca. No district in the world of equal extent is so poor in genera, while those which occur are generally of small size, with scarcely anything remarkable either in colouring or form. The elongated land shells (Clausilia, Buliminus), so characteristic of Europe, are entirely wanting, but a few Bulimulus, of Neotropical origin, penetrate Texas, and from the same sources come a few species of Glandina (as far north as S. Carolina), Holospira (Texas), and Helicina.

The region falls into two well-marked sub-regions, the N. American and the Californian, with the Rocky Mountain district as a sort of debatable ground between them. The Californian sub-region consists of the narrow strip of country between the Sierra Nevada, the Cascade Mountains and the coast-line, from San Diego to Alaska; the N. American sub-region consists of the remainder of the region.

(1) =The N. American Sub-region.=--The Carnivorous genera are represented solely by the few Glandina mentioned above, and by the indigenous genus Selenites, a form midway between Testacella and Limax, whose metropolis is on the Pacific slope, but which spreads eastward into the Antilles. Among the Limacidae, Limax is common to both sub-regions, but Tebennophorus (4 sp., 3 of which belong to the genus Pallifera), a genus found also in China and Siam, and Vitrinozonites do not occur in the Californian. Hyalinia (Zonites) is fairly abundant, especially in the groups Mesomphix and Gastrodonta (peculiar to this sub-region), and Hyalinia proper. Patula is well represented. The Helicidae belong principally to the groups Mesodon, Stenotrema, Triodopsis, Polygyra, and Strobila, only 6 of which, out of a total of 84, reach the Pacific slope. Land operculates are conspicuous for their almost complete absence (see map, frontispiece).

The poverty of the land fauna is atoned for by the extraordinary abundance and variety of the fresh-water genera. A family of operculates, the Pleuroceridae, with 10 genera and about 450 species, is quite peculiar, a few stragglers only reaching Central America and the Antilles. The nucleus of their distribution is the Upper Tennessee River with its branches, and the Coosa River. They appear to dislike the neighbourhood of the sea, and are never found numerously within 100 miles of it. They adhere to stones in rapid water, and differ from the Melaniidae of the Old World and of S. America in the absence of a fringe to the mantle and in being oviparous. They do not occur north of the St. Lawrence River, or north of U.S. territory in the west, or in New England. Three-quarters of all the known species inhabit the rough square formed by the Tennessee River, the Mississippi, the Chattahoochee River, and the Gulf of Mexico. The Mississippi is a formidable barrier to their extension, and a whole section (Trypanostoma, with the four genera Io, Pleurocera, Angitrema, and Lithasia) does not occur west of that river. The Viviparidae are also very largely developed, the genera Melantho, Lioplax, and Tulotoma being peculiar. The Pulmonata are also abundant, while the richness of the Unionidae may be gathered from the fact that Wetherby states[377] that in 1874 no less than 832 species in all had been described.

The entire Mississippi basin is inhabited by a common assemblage of Unionidae, and a considerable number of the species are distributed over the whole of this area, Texas, and parts of E. Mexico. Some species have spread out of this area into Michigan, Canada, the Red River, and Hudson’s Bay district, and even into streams in New York which drain into the Atlantic. An entirely different set of forms occupy the great majority of the rivers falling into the Atlantic, the Appalachian Mountains acting as an effective barrier between the two groups of species, which appear to mingle below the southern end of the range. In many cases Unionidae seem to have no difficulty in migrating from river to river, if the distance is not extreme; they probably are carried across overflowed districts in time of flood.[378]

(2) =The Californian Sub-region= is markedly distinct from the rest of N. America. The characteristic sombre Helices of the Eastern States are almost entirely wanting, and are replaced by Arionta (20 sp.), a larger and more varied group, which may have some affinity to Chinese forms. Glyptostoma (1 sp.) is also peculiar. Selenites here has its metropolis, and Pristiolma is a remarkable group of small Hyalinia (Zonites), but the larger forms of the Eastern States are wanting. Several remarkable and quite peculiar forms of slug occur, namely, Ariolimax (whose nearest relation is Arion), Prophysaon, Hemphillia, and Binneya. There are no land operculates.

Not more than 15 to 20 species of the Pleuroceridae (sect. Goniobasis) occur west of the Rocky Mountains, and only a single Unio, 5 Anodonta, and 1 Margaritana, which is common to New England. Pompholyx is a very remarkable ultra-dextral form of Limnaea, apparently akin to the Choanomphalus of L. Baikal. Bithynia, absent from the Eastern States, is represented by two species. The general indications are in favour of the Californian fauna having migrated from an Old World source after the upheaval of the Sierras; the American fauna, on the other hand, is purely indigenous, with no recent Old World influence at all.

Land Mollusca of the Nearctic Region

Glandina 4 Selenites 6 Limax 4 Vitrina 4 Vitrinozonites 1 Mesomphix 15 Hyalinia 22 Conulus 1 Gastrodonta 9 Pristiloma 2 Tebennophorus 4 Ariolimax 6 Prophysaon 2 Hemphillia 1 Binneya 1 Patula 18 Punctum 2 Arionta 20 Praticola 2 Glyptostoma 1 Mesodon 27 Stenotrema 11 Triodopsis 21 Polygyra 23 Polygyrella 2 Gonostoma 1 Vallonia 1 Strobila 2 Pupa 18 Vertigo 8 Holospira 2 Cionella 1 Bulimulus 6 Macroceramus 1 Succinea 21 Vaginulus 1 Helicina 2

=F. The Neotropical Region=

The land Mollusca of the Neotropical Region stand in complete contrast to those of the Nearctic. Instead of being scanty, they are exceedingly abundant; instead of being small and obscure, they are among the largest in size, most brilliant in colour, and most singular in shape that are known to exist. At the same time they are, as a whole, isolated in type, and exhibit but little relation with the Mollusca of any other region.

The most marked feature is the predominance of the peculiar genera Bulimus and Bulimulus, the centre of whose development appears to lie in Peru, Ecuador, and Bolivia, but which diminish, both in numbers and variety of form, in the eastern portion of the region. In the forests of Central America, Venezuela, and Ecuador, and, to a lesser degree, in those of Peru and Brazil, occurs the genus Orthalicus, whose tree-climbing habits recall the Cochlostyla of the Philippines. These three groups of bulimoid forms constitute, as far as the mainland is concerned, the preponderating mass of the land Mollusca. Helix proper is most strongly developed in the Greater Antilles, which possess several peculiar groups of great beauty. In Central America Helix is comparatively scarce, but in the northern portions of the continent several fine genera (Labyrinthus, Isomeria, Solaropsis) occur, which disappear altogether towards the south.

Carnivorous land Mollusca are, so far as Central America is concerned, more highly developed than in any other quarter of the world, particularly in the genera Glandina and Streptostyla. These genera also penetrate the northern portions of the continent, Glandina reaching as far as Ecuador, and Streptostyla as far as Peru. The Greater Antilles have also characteristic forms of these genera. Streptaxis is tolerably abundant all over tropical South America, and is the one pulmonate genus which shows any affinity with the African fauna.

The slugs are exceedingly scarce. Vaginula occurs throughout, and is the only genus in any sense characteristic.

Clausilia, in the sub-genus Nenia, occurs along the Andean chain from the extreme north (but not in Central America) as far south as Bolivia. It has in all probability made its way into S. America in exceedingly remote ages from its headquarters in Eastern Asia. No species survives in N. America, and a single straggler is found in Porto Rico. The genera Macroceramus, Cylindrella, and Strophia, are characteristic West Indian forms, which are only slightly represented on the mainland. Homalonyx, a curious form akin to Succinea, is peculiar to the region.

Land operculates attain a most extraordinary development in the Greater Antilles, and constitute, in some cases, nearly one-half of the whole Molluscan fauna. Several groups of the Cyclostomatidae find their headquarters here, and some spread no farther. On the mainland this prominence does not continue. West Indian influence is felt in Central America and on the northern coast district, and some Antillean genera make their way as far as Ecuador. The whole group entirely disappears in Chili and Argentina, becoming scarce even in Brazil.

Among the fresh-water operculates, Ampullaria is abundant, and widely distributed. Vivipara, so characteristic of N. America, is entirely absent. Chilina, a remarkable fresh-water pulmonate, akin to Limnaea, is peculiar to Chili, Patagonia, and Southern Brazil, but is not found in the tropical portion of the continent. Of the fresh-water Pelecypoda Mycetopus, Hyria, Castalia, Leila, and Mülleria are peculiar forms, akin to the Unionidae.

(1) =The Antillean Sub-region= surpasses all other districts in the world in respect of (1) extraordinary abundance of species, (2) sharp definition of limits as a whole, (3) extreme localisation of the fauna of the separate islands. The sub-region includes the whole of the half-circle of islands from the Bahamas to Grenada, together with the extreme southern end of the peninsula of Florida, which was once, no doubt, a number of small islands like the Bahamas. Trinidad, and probably Tobago, although containing an Antillean element, belong to the mainland of S. America, from which they are only separated by very shallow water.

The sub-region appears to fall into four provinces:--

(a) Cuba, the Bahamas, and S. Florida; (b) Jamaica; (c) San Domingo (Haiti), Porto Rico, and the Virgin Is., with the Anguilla and St. Bartholomew group; (d) the islands from Guadeloupe to Grenada. The first three provinces contain the mass of the characteristic Antillean fauna, the primary feature being the extraordinary development of the land operculates, which here reaches a point unsurpassed in any other quarter of the globe. The relative numbers are as follows:--

Cuba Jamaica San Domingo Porto Rico

Inoperculate 362 221 152 75 Operculate 252 242 100 23

It appears, then, that the proportion of operculate to inoperculate species, while very high in Cuba (about 41 per cent of the whole), reaches its maximum in Jamaica (where the operculates are actually in a majority), begins to decline in San Domingo (about 40 per cent), and continues to do so in Porto Rico, where they are not more than 24 per cent of the whole. These operculates almost all belong to the families Cyclostomatidae and Helicinidae, only two genera (Aperostoma and Megalomastoma) belonging to the Cyclophorus group. Comparatively few genera are absolutely peculiar to the islands, one or two species of most of them occurring in Central or S. America, but of the several hundreds of operculate species which occur on the islands, not two score are common to the mainland.

The next special feature of the sub-region is a remarkable development of peculiar sub-genera of Helix. In this respect the Antilles present a striking contrast to both Central and S. America, where the prime feature of the land Pulmonata is the profusion of Bulimus and Bulimulus, and Helix is relatively obscured. No less than 14 sub-genera of Helix, some of which contain species of almost unique beauty and size, are quite peculiar to the Greater Antilles, and some are peculiar to individual islands.

Here, too, is the metropolis of Cylindrella (of which there are 130 species in Cuba alone), a genus which just reaches S. America, and has a few species along the eastern sea-board of the Gulf of Mexico. Macroceramus and Strophia are quite peculiar; the former, a genus allied to Cylindrella, which attains its maximum in Cuba and San Domingo, is scarcely represented in Jamaica, and disappears south of Anguilla; the latter, a singular form, resembling a large Pupa in shape, which also attains its maximum in Cuba, is entirely wanting in Jamaica, and has its last representative in S. Croix. One species irregularly occurs at Curaçao.

The carnivorous group of land Mollusca are represented by several peculiar forms of Glandina, which attain their maximum in Jamaica and Cuba, but entirely disappear in the Lesser Antilles.

A certain number of the characteristic N. American genera are found in the Antillean Sub-region, indicating a former connexion, more or less intimate, between the W. Indies and the mainland. The genera are all of small size. The characteristic N. American Hyalinia are represented in Cuba, San Domingo, and Porto Rico; among the Helicidae, Polygyra reaches Cuba, but no farther, and Strobila Jamaica. The fresh-water Pulmonata are of a N. American type, as far as the Greater Antilles are concerned, but the occurrence of Gundlachia (Tasmania and Trinidad only) in Cuba is an unexplained problem at present. Unionidae significantly occur only at the two ends of the chain of islands, not reaching farther than Cuba (Unio 3 sp.) at one end, and Trinidad (which is S. American) at the other.

A small amount of S. American influence is perceptible throughout the Antilles, chiefly in the occurrence of a few species of Bulimulus and Simpulopsis. The S. American element may have strayed into the sub-region by three distinct routes: (1) by way of Trinidad, Tobago, and the islands northward; (2) by a north-easterly extension of Honduras towards Jamaica, forming a series of islands of which the Rosalind and Pedro banks are perhaps the remains; (3) by a similar approximation of the peninsula of Yucatan and the western extremity of Cuba. Central America is essentially S. American in its fauna, and the characteristic genera of Antillean operculates which occur on its eastern coasts are sufficient evidence of the previous existence of a land connexion more or less intimate (see map).

(a) Cuba is by far the richest of the Antilles in land Mollusca, but it must be remembered that it is also much better explored than San Domingo, the only island likely to rival it in point of numbers. It contains in all 658 species, of which 620 are land and 38 fresh-water, the land operculates alone amounting to 252.

Carnivorous genera form but a small proportion of the whole. There are 18 Glandina (which belong to the sections Varicella and Boltenia) and 4 Streptostyla, the occurrence of this latter genus being peculiar to Cuba and Haiti (1 sp.) among the Antilles, and associating them closely with the mainland of Central America, where Streptostyla is abundant. These two genera alone represent the Agnatha throughout the sub-region.

There are no less than 84 species of Helix, belonging to 12 sub-genera. Only one of these (Polymita) is quite peculiar to Cuba, but of 7 known species of Jeanerettia and 8 of Coryda, 6 and 7 respectively are Cuban. Thelidomus has 15 species (Jamaica 3, Porto Rico 3); Polydontes has 3, the only other being from Porto Rico; Hemitrochus has 12 (Jamaica 1, Bahamas 6); Cysticopsis 9 (Jamaica 6); Eurycampta 4 (Bahamas 1).

The Cylindrellidae find their maximum development in Cuba. As many as 34 Macroceramus occur (two-thirds of the known species), and 130 Cylindrella, some of the latter being most remarkable in form (see Fig. 151, B, p. 247).

The land operculates belong principally to the families Cyclostomatidae and Helicinidae. Of the former, Cuba is the metropolis of Ctenopoma and Chondropoma, the former of which includes 30 Cuban species, as compared with 1 from San Domingo and 2 from Jamaica. Megalomastoma (Cyclophoridae) is also Haitian and Porto Rican, but not Jamaican. Blaesospira, Xenopoma, and Diplopoma are peculiar. The Helicinidae consist mainly of Helicina proper (58 sp.), which here attains by far its finest development in point of size and beauty, and of Eutrochatella (21 sp.), which is peculiar to the three great islands (Jamaica 6 sp., San Domingo 6 sp.).

The Bahamas, consisting in all of more than 700 islands, are very imperfectly known, but appear to be related partly to Cuba, partly to San Domingo, from each of which they are separated by a narrow channel of very deep water. They are certainly not rich in the characteristic groups of the Greater Antilles. The principal forms of Helix are Plagioptycha (6 sp.), common with San Domingo, and Hemitrochus (6 sp.), common with Cuba. Strophia is exceedingly abundant, but Cylindrella, Macroceramus, and Glandina have but few species. There are a few species of Ctenopoma, Chondropoma, and Cistula, while a single Schasicheila (absent from the rest of the sub-region) forms a link with Mexico.

Southern Florida, with one or two species each of Hemitrochus, Cylindrella, Macroceramus, Strophia, Ctenopoma, and Chondropoma, belongs to this province.

(b) Jamaica.--The land Mollusca of Jamaica are, in point of numbers and variety, quite unequalled in the world. There are in all as many as 56 genera and more than 440 species, the latter being nearly all peculiar. The principal features are the Glandinae, the Helicidae, and the land operculates. The Glandinae belong principally to the sub-genera Varicella, Melia, and Volutaxis, Streptostyla being absent, although occurring in Cuba and San Domingo. There are 10 genera of Helix, of which Pleurodonta is quite peculiar, while Sagda (13 sp.) is common only with S.W. San Domingo (2 sp.), and Leptoloma (8 sp.) only with Cuba (1 sp.). The single Strobila seems to be a straggler from a N. American source. Macroceramus has only 2 species as against 34 in Cuba, and of Cylindrella, in which Cuba (130 sp.) is so rich, only 36 species occur. The genus Leia, however (14 sp.), is all but peculiar, occurring elsewhere only in the neighbouring angle of San Domingo, which is so closely allied with Jamaica. The complete absence of Strophia is remarkable.

The land operculates form the bulk of the land fauna, there being actually 242 species, as against 221 of land Pulmonata, a proportion never again approached in any part of the world. As many as 80 of these belong to the curious little genus Stoastoma, which is all but peculiar to the island, one species having been found in San Domingo, and one in Porto Rico. Geomelania and Chittya, two singular inland forms akin to Truncatella, are quite peculiar. Alcadia reaches its maximum of 14 species, as against 4 species in San Domingo and 9 species in Cuba, and Lucidella is common to San Domingo only; but, if Stoastoma be omitted, the Helicinidae generally are not represented by so many or by so striking forms as in Cuba, which has 90 species, as against Jamaica 44, and San Domingo 35.

(c) San Domingo, although not characterised by the extraordinary richness of Cuba and Jamaica, possesses many specially remarkable forms of land Mollusca, to which a thorough exploration, when circumstances permit, will no doubt make important additions. From its geographical position, impinging as it does on all the islands of the Greater Antilles, it would be expected that the fauna of San Domingo would not exhibit equal signs of isolation, but would appear to be influenced by them severally. This is exactly what occurs, and San Domingo is consequently, although very rich in peculiar species, not equally so in peculiar genera. The south-west district shows distinct relations with Jamaica, the Jamaican genera Leia, Stoastoma, Lucidella, and the Thaumasia section of Cylindrella occurring here only. The north and north-west districts are related to Cuba, while the central district, consisting of the long band of mountainous country which traverses the island, contains the more characteristic Haitian forms.

The Helicidae are the most noteworthy of the San Domingo land Mollusca. The group Eurycratera, which contains some of the finest existing land snails, is quite peculiar, while Parthena, Cepolis, Plagioptycha, and Caracolus here reach their maximum. The Cylindrellidae are very abundant, but no section is peculiar. Land operculates do not bear quite the same proportion to the Pulmonata as in Cuba and Jamaica, but they are well represented (100 to 152); Rolleia is the only peculiar genus.

The relations of San Domingo to the neighbouring islands are considerably obscured by the fact that they are well known, while San Domingo is comparatively little explored. To this may perhaps be due the curious fact that there are actually more species common to Cuba and Porto Rico (26) than to Porto Rico and San Domingo. Cuba shares with San Domingo its small-sized Caracolus and also Liguus, but the great Eurycratera, Parthena, and Plagioptycha are wholly wanting in Cuba. The land operculates are partly related to Cuba, partly to Jamaica, thus Choanopoma, Ctenopoma, Cistula, Tudora, and many others, are represented on all these islands, while the Jamaican Stoastoma occurs on San Domingo and Porto Rico, but not on Cuba, and Lucidella is common to San Domingo and Jamaica alone. An especial link between Jamaica and San Domingo is the occurrence in the south-west district of the latter island of Sagda (2 sp.). The relative numbers of the genera Strophia, Macroceramus, and Helicina, as given below (p. 351), are of interest in this connexion.

Porto Rico, with Vièque, is practically a fragment of San Domingo. The points of close relationship are the occurrence of Caracolus, Cepolis, and Parthena among the Helicidae, and of Simpulopsis, Pseudobalea, and Stoastoma. Cylindrella and Macroceramus are but poorly represented, but Strophia still occurs. The land operculates (see the Table) show equal signs of removal from the headquarters of development. Megalomastoma, however, has some striking forms. The appearance of a single Clausilia, whose nearest relations are in the northern Andes, is very remarkable. Gaeotis, which is allied to Peltella (Ecuador only), is peculiar.

Land Mollusca of the Greater Antilles

Cuba. Jamaica. S. Domingo. Porto Rico.

Glandina 18 24 15 8 Streptostyla 4 ... 2 ... Volutaxis ... 11 (?) 1 ... Selenites 1 ... ... ... Hyalinia 4 11 5 6 Patula 5 1 ... ... Sagda ... 13 2 ... Microphysa 7 18 8 3 Cysticopsis 9 6 ... ... Hygromia (?) ... ... 3 ... Leptaxis (?) ... ... 1 ... Polygyra 2 ... ... ... Jeanerettia 6 ... ... 1 Euclasta ... ... ... 4 Plagioptycha ... ... 14 2 Strobila ... 1 ... ... Dialeuca ... 1 ... ... Leptoloma 1 8 ... ... Eurycampta 4 ... ... ... Coryda 7 ... ... ... Thelidomus 15 3 ... 3 Eurycratera ... ... 7 ... Parthena ... ... 2 2 Cepolis ... ... 3 1 Caracolus 8 ... 6 2 Polydontes 3 ... ... 1 Hemitrochus 12 1 ... ... Polymita 5 ... ... ... Pleurodonta ... 34 ... ... Inc. sed. 5 ... ... ... Simpulopsis ... ... 1 1 Bulimulus 3 3 6 7 Orthalicus 1 1 ... ... Liguus 3 ... 1 ... Gaeotis ... ... ... 3 Pineria 2 ... ... 1 Macroceramus 34 2 14 3 Leia ... 14 2 ... Cylindrella 130 36 35 3 Pseudobalea 2 ... 1 1 Stenogyra 6 7 (?) ... Opeas 8 (?) 4 6 Subulima 6 14 2 2 Glandinella 1 ... ... ... Spiraxis 2 (?) 2 1 Melaniella 7 ... ... ... Geostilbia 1 ... 1 ... Cionella 2 ... ... ... Leptinaria ... 1 ... 3 Obeliscus ... ... 1 2 Pupa 2 7 3 2 Vertigo 4 ... ... ... Strophia 19 ... 3 2 Clausilia ... ... ... 1 Succinea 11 2 5 3 Vaginula 2 2 2 1 Megalomastoma 13 ... 1 3 Neocyclotus 1 33(?) ... ... Licina 1 ... 3 ... Jamaicia ... 2 ... ... Crocidopoma ... 1 3 ... Rolleia ... ... 1 ... Choanopoma 25 12 19 3 Ctenopoma 30 2 1 ... Cistula 15 3 3 3 Chondropoma 57 (?) 19 4 Tudora 7 17 5 ... Adamsiella 1 12 ... ... Blaesospira 1 ... ... ... Xenopoma 1 ... ... ... Cistula 15 3 3 ... Colobostylus 4 13 5 ... Diplopoma 1 ... ... ... Geomelania ... 21 ... ... Chittya ... 1 ... ... Blandiella ... ... 1 ... Stoastoma ... 80 1 1 Eutrochatella 21 6 6 ... Lucidella ... 4 1 ... Alcadia 9 14 4 ... Helicina 58 16 24 9 Proserpina 2 4 ... ...

The Virgin Is., with St. Croix, Anguilla, and the St. Bartholomew group (all of which are non-volcanic islands), are related to Porto Rico, while Guadeloupe and all the islands to the south, up to Grenada (all of which are volcanic), show marked traces of S. American influence. St. Kitt’s, Antigua, and Montserrat may be regarded as intermediate between the two groups. St. Thomas, St. John, and Tortola have each one Plagioptycha and one Thelidomus, while St. Croix has two sub-fossil Caracolus which are now living in Porto Rico, together with one Plagioptycha and one Thelidomus (sub-fossil). The gradual disappearance of some of the characteristic greater Antillean forms, and the appearance of S. American forms in the Lesser Antilles, is shown by the following table:--

+-----------------------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | | | | | | | | | | | | | | | S | | | | | P | S | | | | | S | | G | | M | | | t | | | | | o | t | | S | | | t | | u | | a | S | | . | | | | | r | . | | t | | A | . | | a | D | r | t | B | | | T | | | t | | S | . | T | n | | A | d | o | t | . | a | V | G | r | | | o | T | t | | o | g | K | n | e | m | i | | r | i | r | i | | | | h | . | C | r | u | i | t | l | i | n | L | b | n | e | n | | | R | o | | r | t | i | t | i | o | n | i | u | a | c | n | i | | | i | m | J | o | o | l | t | g | u | i | q | c | d | e | a | d | | | c | a | a | i | l | l | ’ | u | p | c | u | i | o | n | d | a | | | o | s | n | x | a | a | s | a | e | a | e | a | s | t | a | d | | | . | . | . | . | . | . | . | . | . | . | . | . | . | . | . | . | +-----------------------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | Bulimulus | 7 | 4 | 2 | 4 | 1 | 2 | 2 | 3 | 8 | 9 | 5 | 3 | 3 | 6 | 2 | 4 | | Cylindrella | 3 | 2 | 1 | 1 | 1 | . | . | . | 1 | . | 1 | 1 | 1 | . | . | 1 | | Macroceramus | 3 | 1 | 1 | . | 2 | 1 | . | . | . | . | . | . | . | . | . | | | Cyclostomatidae, etc. |23 | 4 | 1 | 5 | 1 | 1 | 1 | . | 4 | . | . | . | . | . | . | 1 | | Dentellaria | . | . | . | . | . | . | 1 | 1 | 8 | 5 |11 | 2 | 2 | . | 1 | 1 | | Cyclophorus | . | . | . | . | . | . | . | . | 1 | 2 | 2 | . | . | . | . | . | | Amphibulimus | . | . | . | . | . | . | . | . | 2 | 3 | 1 | . | . | . | . | . | | Homalonyx | . | . | . | . | . | . | . | . | 1 | 1 | . | . | . | . | . | . | +---------------------------------------------------------------------------------------+

(d) In Guadeloupe we find Cyclophorus, Amphibulimus, Homalonyx, and Pellicula, which are characteristic of S. America, and nearly all recur in Dominica and Martinique. These islands are the metropolis of Dentellaria, a group of Helix, evidently related to some of the forms developed in the Greater Antilles. Stragglers occur as far north as St. Kitt’s and Antigua, and there are several on the mainland as far south as Cayenne. Traces of the great Bulimus, so characteristic of South America, occur as far north as S. Lucia, where also is found a Parthena (San Domingo and Porto Rico). Trinidad is markedly S. American; 55 species in all are known, of which 22 are peculiar, 28 are common to S. America (8 of these reach no farther north along the islands), and only 5 are common to the Antilles, but not to S. America. The occurrence of Gundlachia in Trinidad has already been mentioned.

The Bermudas show no very marked relationship either to the N. American or to the West Indian fauna. In common with the former they possess a Polygyra, with the latter (introduced species being excluded) one species each of Hyalosagda, Subulina, Vaginula, and Helicina, so that, on the whole, they may be called West Indian. The only peculiar group is Poecilozonites, a rather large and depressed shell of the Hyalinia type.

(2) =The Central American Sub-region= may be regarded as extending from the political boundary of Mexico in the north to the isthmus of Panama in the south. It thus impinges on three important districts--the N. American, West Indian, and S. American; and it appears, as we should perhaps expect, that the two latter of these regions have considerably more influence upon its fauna than the former. Of the N. American Helicidae, Polygyra is abundant in Mexico only, and two species of Strobila reach N. Guatemala, while the Californian Arionta occurs in Mexico. S. American Helicidae, in the sub-genera Solaropsis and Labyrinthus, occur no farther north than Costa Rica. Not a single representative of any of the characteristic West Indian Helicidae occurs. Bulimulus and Otostomus, which form so large a proportion of the Mollusca of Venezuela, Colombia, Ecuador, and Peru, together with Orthalicus, are abundant all over the region. Again, Cylindrella, Macroceramus, and some of the characteristic Antillean operculates, are represented, their occurrence being in most cases limited to the eastern coast-line and eastern slope of the central range.

Besides these external elements, the region is rich in indigenous genera. Central America is remarkable for an immense number of large carnivorous Mollusca possessing shells. There are 49 species of Glandina, the bulk of which occur in eastern and southern Mexico; 36 of Streptostyla (S.E. Mexico and Guatemala, only 1 species reaching Venezuela and another Peru); 5 of Salasiella, 2 of Petenia, and 1 of Strebelia; the last three genera being peculiar. Streptaxis, fairly common in S. America, does not occur. Velifera and Cryptostracon, two remarkable slug-like forms, each with a single species, are peculiar to Costa Rica. Among the especial peculiarities of the region are the giant forms belonging to the Cylindrellidae, which are known as Holospira, Eucalodium, and Coelocentrum (Fig. 232). They are almost entirely peculiar to Mexico, only 7 out of a total of 33 reaching south of that district, and only 1 not occurring in it at all.

The land operculates are but scanty. Tomocyclus and Amphicyclotus are peculiar, and Schasicheila, a form of Helicina, occurs elsewhere only in the Bahamas. Ceres (see Fig. 18, C, p. 21) and Proserpinella, two remarkable forms of non-operculate Helicinidae (compare the Chinese Heudeia), are quite peculiar. Pachychilus, one of the characteristic fresh-water genera, belongs to the S. American (Melaniidae) type, not to the N. American (Pleuroceridae). Among the fresh-water Pulmonata, the Aplecta are remarkable for their great size and beauty. In the accompanying table “Mexico” is to be taken as including the region from the United States border up to and including the isthmus of Tehuantepec, and “Central America” as the whole region south of that point.

Land Mollusca of Central America

Mexico only. Central Common to America both. only.

Strebelia 1 ... ... Glandina 33 13 3 Salasiella 4 ... 1 Streptostyla 18 12 6 Petenia ... 1 1 Limax ... 1 ... Velifera ... 1 ... Omphalina 10 1 1 Hyalinia 2 5 3 Guppya ... 8 3 Pseudohyalina 2 ... 2 Tebennophorus 1 ... ... Cryptostracon ... 1 ... Xanthonyx 4 ... ... Patula 3 ... 4 Acanthinula 1 2 2 Vallonia ... 1 ... Trichodiscus 2 2 3 Praticolella 1 ... 1 Arionta 3 ... ... Lysinoe 1 1 1 Oxychona 2 5 ... Solaropsis ... 2 ... Polygyra 14 1 2 Strobila 1 1 ... Labyrinthus ... 5 ... Otostomus 23 20 7 Bulimulus 6 5 2 Berendtia 1 ... ... Orthalicus 6 3 3 Pupa 1 1 1 Vertigo 1 ... ... Holospira 12 ... ... Coelocentrum 6 1 1 Eucalodium 15 ... 5 Cylindrella 6 4 ... Macroceramus 2 1 ... Simpulopsis 2 1 ... Caecilianella 1 ... ... Opeas 1 2 3 Spiraxis 8 2 1 Leptinaria ... 2 ... Subulina 2 3 4 Succinea 11 3 1 Vaginula 1 ... ... Aperostoma ... 4 1 Amphicyclotus 2 1 2 Cystopoma 2 ... ... Tomocyclus ... 1 2 Choanopoma 2 2 ... Chondropoma 2 11 ... Helicina 13 10 6 Schasicheila 2 ... 1 Ceres 2 ... ... Proserpinella 1 ... ...

(3) =The Colombian Sub-region= includes Colombia, New Grenada, Venezuela, Guiana, Ecuador, Peru, and Bolivia. It has been usual to separate off the two latter countries as forming a distinct “Peruvian” sub-region; but there is, as will be seen, absolutely no line to be drawn between the Mollusca of Peru and those of Ecuador; nor would one, on geographical considerations, expect to be able to draw such a line. A better method of subdivision, so far as the species of the whole eastern portion of the region are concerned, would be to group the Mollusca according to the altitude at which they occur, were it not that the evidence on this point is at present but fragmentary. We know, however, that all along the line of the Andes certain species, more particularly of Bulimulus, occupy their own zones of elevation, some ascending as high as 10,000 feet above the sea, and never occurring on the plains.

In the northern portions of this sub-region, Central American and West Indian influence is felt to a certain extent. Thus there are eight Glandina and one Streptostyla in Venezuela and Colombia together with one or two species of Cistula, Chondropoma, Proserpina, and Cylindrella, while a single Strophia (decidedly a straggler) occurs at Curaçao. In Demerara and Cayenne there are three or four species of Dentellaria. In Ecuador, however, Glandina diminishes to three species, and in Peru disappears altogether, although one Streptostyla occurs. Similarly the West Indian operculates are reduced to one Chondropoma (Ecuador) and disappear entirely in Peru.

The Helicidae are most abundant in the north and west, and are represented by several very striking sub-genera, some of which possess remarkably toothed apertures, and perhaps betray an ancestry common to some of the West Indian genera. Of these, Labyrinthus has 12 species in Venezuela and Colombia, 5 in Ecuador, and 3 in Peru and Bolivia; Isomeria 12 in Venezuela and Colombia, 20 in Ecuador, and 2 in Peru and Bolivia; Salaropsis is represented in these countries by 6, 3, and 7 species, and Systrophia by 4, 5, and 8 species respectively.

Clausilia--in the group Nenia--appears in some numbers along the Andes chain, the only other representative in the New World being the solitary species occurring at Porto Rico. There have been described, from Venezuela and Colombia 10 species, from Ecuador 5, and from Peru and Bolivia 12.

Another marked feature of the region is the occurrence of the Orthalicidae, in the two genera Orthalicus and Porphyrobaphe. The latter of these magnificent forms is peculiar, while the former reaches Mexico, the West Indies, and Brazil. Ecuador, which contains 23 species, seems the metropolis of the group.

Bulimus and Bulimulus, the former genus being peculiar to S. America and the adjacent islands, are largely represented, the former in the three groups Borus, Dryptus, and Orphnus. These attain their maximum in Peru, with 25 species, but Venezuela and Colombia have as many as 17. Bulimulus has been subdivided into a number of groups, e.g. Drymaeus, Mesembrinus, Thaumastus, Mormus, Scutalus, with many others,--the exact scientific limits of which are not easily discernible. It must suffice here to state that Peru seems to be the headquarters of the group with about 190 species (which probably may well be reduced), Ecuador having about 70, and Venezuela and Colombia between 80 and 90.

Two very remarkable forms belonging to the Pupidae, Anostoma (Fig. 154, p. 248) and Tomigerus, occur in Venezuela, the metropolis. Rhodea, another very peculiar shell (Fig. 234), whose exact family position is uncertain, is peculiar to New Grenada. The land operculates are few in number, and in Bolivia almost disappear. They belong principally to Neocyclotus (of which 11 species occur in Venezuela and Colombia) and Helicina (10 species in the same district), besides the stragglers already mentioned from West Indian sources, and a few Cyclophorus. Bourcieria is a form of Helicina peculiar to Ecuador. Ampullaria, with Ceratodes, a peculiar planorbiform sub-genus, and Hemisinus, form the bulk of the fresh-water operculates.

The Galapagos.--Thirty-four species of land Mollusca, all peculiar, are known from these islands; 25 of these are forms of Bulimulus. There are no Helicidae, one each of Hyalinia, Leptinaria, and Helicina, and two Pupa. The Bulimulus are mostly of the group Nesiotis, and in their brown colour bear some outward resemblance to the dark Achatinella of the Sandwich Is., living as they do mostly under scoriae on the ground, and not on trees. In type, however, they appear to be derived from Chili and Peru, rather than from the parts of S. America immediately contiguous. Another section (Pleuropyrgus 2 sp.) closely resembles a marine Chemnitzia. The islands are all volcanic, and are probably not the result of subsidence; thus the existing species are not to be regarded as the relics of a more widespread fauna, but as a new set of inhabitants.

(4) =The Brazilian Sub-region.=--This immense district is very little known, except in the south, and it is consequently impossible to give any satisfactory account of its Mollusca. It is possible that eventually it will be found that it falls into provinces which correspond more or less to (a) the Amazon basin; (b) the mountainous district in the east, drained by the Tocantins and the San Francisco; (c) the Parana basin in the south central district; and (d) the Argentine or Pampas district in the extreme south. But at present the data are insufficient to establish any such subdivisions, whose existence, if proved, would have an important bearing on the problem of the coalescence of S. America into its present form.[379]

The Agnatha are represented by Streptaxis alone (17 sp.). Helix is rare, but includes the peculiar Polygyratia (Fig. 150 A, p. 246), while Labyrinthus (2 sp.), Solaropsis (5 sp.), and Systrophia are common with the Colombian Sub-region, and Oxychona (4 sp.) with the Central American. Bulimus has in all 36 species, the sub-genera Pachyotus (Fig. 233) and Strophochilus being peculiar. Bulimulus, though not so abundant as in Peru and Ecuador, has about 60 species, of which Navicula (Fig. 235) is the most remarkable group. Megaspira is peculiar. Orthalicus has only 4 species, while Tomigerus (4 sp.) and Anostoma (3 sp.) are common with Venezuela. Land operculates are scarce, and appear to include only Neocyclotus, Cyclophorus, and Helicina.

In Argentina, which may probably rank as a separate province, the tropical forms greatly decrease, Streptaxis being reduced to 2 species, and Bulimus and Bulimulus together to 40, while Orthalicus, the great Helices, and the land operculates disappear altogether. Odontostomus (Fig. 236), a genus of the Pupidae, is abundant in the northern part of the province. Two or three species of Chilina occur.

(5) =The Chilian Sub-region.=--The greater part of Chili, from its arid and rainless climate, is unfavourable to the existence of land Mollusca. Bulimus (Borus) still has 3 or 4 species, and Bulimulus (Plectostylus 11, Scutalus 9, Peronaeus 7) is fairly abundant, but the profusion of the tropics is wanting. There are no carnivorous genera, and only two land operculates. A remarkable form of Helix (Macrocyclis, Fig. 237) is quite peculiar, but the majority of the species belong to two rather obscure groups, Stepsanoda and Amphidoxa. Chilina, a singularly solid form of Limnaea (of which 8 sp., with a sub-genus Pseudochilina, occur in Chili), is peculiar to Chili, S. Brazil, and Patagonia. From the two islands of Juan Fernandez and Masafuera, are known several Helix, of Chilian affinity, several curious Succinea, a Homalonyx, Leptinaria, and Nothus, and three species of Tornatellina, with the almost universal Limax gagates.

The question of the existence at some remote period of a Neantarctic continent, which formed a communication between the three great southern peninsulas of the world, is one on which the Mollusca may offer evidence. Von Ihering holds that an essential difference can be observed between certain of the Unionidae which inhabit S. America, Africa, and Australia with New Zealand, and those which inhabit Europe, Asia, and N. America, but the point can hardly be regarded as definitely established at present. Something perhaps may be made of the distribution of Bulimus and Bulimulus. It seems difficult to explain the occurrence of sub-fossil Bulimus on St. Helena except on some such lines as have been recently adduced to account for the presence of struthious birds in the Mascarenes, and possibly the form Livinhacea may be a trace of the same element in S. Africa. Again, the Liparus of S. and W. Australia, with the Caryodes of Tasmania, and the Leucotaenia and Clavator of Madagascar (which all may be related to Bulimus), together with the Placostylus of New Caledonia and the adjacent islands, reaching even to New Zealand, and perhaps even the Amphidromus of Malaysia (which are more akin to Bulimulus), may be thought to exhibit, in some remote degree, traces of a common ancestry.

The land operculates give no help, and, of the carnivorous genera, Rhytida is a marked link between Africa and Australia, while Streptaxis is equally so between S. America and Africa. As regards fresh-water Gasteropoda, Ampullaria is common to S. America and Africa, while Isidora is common to Africa, Australia, and New Zealand, but is altogether absent from S. America. Gundlachia occurs in Florida, Trinidad, and Tasmania, but has not been detected in Africa. It must be concluded, therefore, that the present state of the evidence which the Mollusca can afford, while exhibiting certain curious points of relationship between the three regions in question, is insufficient to warrant any decided conclusion.

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