446 WEST INDIAN MOLLUSKS— SIMPSON. vol. xvii. 



for tlie most part derived from South America. At Triuidad — wbicli 

 is merely a detached fragment of Veueziiehi — more than half the species 

 are common to the mainland, and among them are one or more of the 

 continental Bonis, an Ampullarid, a Marua, and an Anodon.* 



Boms is found in St. Vincent, Barbados, Guadeloupe, St. Kitts, and 

 Montserrat,t and Bulimuhis, another most characteristic South Ameri- 

 can genus is abundant throughout the Lesser Antilles. The 500-fathom 

 line will be found to divide the Lesser Antilles into three groups; the 

 most northern embracing every island from Sombrero and the Saba 

 bank south to and including Dominica. Between the latter and Mar- 

 tinique is a channel 575 fathoms in depth, and south of it is another of 

 548 fathoms. Beginning with St. Lucia, which is separated from St. 

 Vincent by a depth of 48(3 fathoms, all the islands to the southward are 

 united to the mainland by the 500-fathom line. Barbados is somewhat 

 isolated, and is surrounded by comparatively deep water, being sep. 

 arated from the chain by 1,403 fathoms, while Trinidad, Tobago, Mar- 

 garita, and Tortuga are all Avithin the 100-fathom line. Several South 

 American Bulimus typified by B. anyis-sileni are found in the islands 

 from St. Vincent soutlnvard, and Martinique, which is separated from 

 the islands north and south of it by channels over 500 fathoms in depth, 

 has no Pineria, Ghondropoma, Gho((nopoma, or Cisttdaj which are Greater 

 Antillean genera found in the Windward Islands north of it. As a proof 

 of the comparative x^overty of the Lesser Antilles it may be stated 

 that the whole archipehigo does not contain 300 species of terrestial 

 and tluviatile mollusks; scarcely more than half the number belonging 

 to Jamaica. 



One group is found in nearly all the Windward Islands, Gaprinus 

 (better known as IfentcUaria), a section of the genus Plenrodonte, which 

 seems to bear about equal relationship to the sections found in the 

 Greater Antilles, and to Lahyrinthus of northern South America. There 

 is another division of the genus, Isomcria, which is confined for the most 

 part to the higher Andean regions of Peru, Equador, and Colombia, 

 characterized by a lesser development of teeth in the aperture t^mw Lahy- 

 rinthus, and which may have sprung from the latter. The distribu- 

 tion of these groups is a little peculiar. We may suppose the Greater 

 Antilles to be the site whereon Pleurodonte developed, from the fact that 

 six out of the eleven of its sections are wholly confined to that region, as 

 is another, Thelidomns, with the exception of a couple of species, while a 

 majority of the species of the genus are also found there. It would seem 

 strange that some ancestral form which had migrated to the Lesser 



*The latter is a Glabaris no doubt. Ihering lias shown (Archiv fiir Naturges- 

 chicbte .Jalirg 59, 1 Bel., 1 Heft., p. 52), that all the Sonth American Anodons, so 

 called, are aiiatoniically quite distinct from the Uuionidie, and that they belong to 

 the Mutelidie. This form, A. leotandi, Guppy, is no doubt derived from some of the 

 continental species. 



t Introduced into the more northern islands, probably on coffee trees. 



