London: Stanford’s Geogḷ Estabṭ.
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).