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).