432 WEST IXDIAN MOLLUSES— SIMPSON. vol. xvii. 



1,023 species. Seven of these genera are found in all four of the larger 

 islands; Thysanophora, Hemitrochus, Pleurodonte, Cylindrella, Maero- 

 ceramus, Choanopoma, and Cistula, with 514 species in this region; 

 while twelve more, Sagda, Gerion, Geomelania, Megalomastoma, 

 Crocidopoma, Ctenopoma, Chondropoma, Tudora, Colobostylus, Eutro- 

 chatella, Alcadia, and Stoastoma, represented by 401 species, are found 

 in three or a majority of the islands. 



Of the remainder of the Greater Antillean genera nine are found in 

 two islands, Cepolis, Liguus, Vendryesia, Pineria, Proserpina, Neocyclo- 

 tus, Licina, Adamsiella, and Lucidella, with only 84 species, and 9 are 

 limited to a single island, Zaphysema, Polymita, Glandinella, Melaniella, 

 Bolleia, Jamaicia, Diplopoma, Blcesospira and Xenopoma, with but 24 

 species. 



Of the widely distributed genera whose metropolis is elsewhere, and 

 which we may suppose have entered this region by some of the means 

 I have previously mentioned, 16 are found in all four of the islands, 

 represented by 371 species; 6 are met with in three of the islands, with 

 33 species; 10 in two of them, with 31 species, while only 7 genera are 

 found limited to a single island, six of them having but 1 species each, 

 and one having 13 species. 



From the above figures the remarkably homogeneous character of the 

 terrestrial and fluviatile molluscan fiiuna of the Greater Antilles may be 

 understood, for out of 78 genera here represented by about 1,400 spe- 

 cies, 22, nearly one-third of them, are met with in all four of the islands, 

 having 885 species, or more than 60 per cent of the whole number; and 

 18 others are common to three of the islands, with 434 species. It will 

 thus be seen that nearly all the important genera have a general dis- 

 tribution in this region, and are largely represented in species. 



Now, while it is true that certain genera and minor groups are pecul- 

 iar in some cases to a single island, as, for example, the typical Pleuro- 

 dontes, Zaphysema, and Ptychocochlis to Jamaica, Polymita, and Diplo- 

 poma to Cuba, Rolleia to Haiti, or Luquillia to Puerto Rico, yet it is no 

 doubt equally true that the relationship between them and certain 

 groups found on other islands of this archipelago is quite close. The 

 toothless or slightly toothed Pleurodontes of Jamaica are not very far 

 removed from (larocolus; Dialeuca, also a Jamaican grouj), is very closely 

 allied to the Cordyas of Cuba and Haiti, and Pilsbry has shown* that 

 Zaphysema, Thysanophora, and Sagda are quite intimately related. Such 

 alliances between the species of the different islands are very com- 

 mon, especially among the Helicidne, Cylindrella, Macroceramus, the 

 Alcadias, and Helicinas. In short, there can be but little doubt that 

 all or nearly all the special groups confined to one or more of these 

 islands are much more nearly related to other Greater Antillean groups 

 than to those of any other part of the world. 



This period of elevation in the West Indies was followed by one of 



*Manual of Conchology, second series, ix, p. 60. 



