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.
Map to illustrate the
GEOGRAPHICAL DISTRIBUTION
of the Land Mollusca of the
WEST INDIES.
The red line marks the 100 fathom line.
London: Macmillan and Cọ.