_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. [Illustration: FIG. 228.--_Homalonyx unguis_ Fér., Demerara. _sh_, Shell (shown also separate); _p.o_, pulmonary orifice.] 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