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

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—

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

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—

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

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.