OP CONCHOLOGY. 139 



I may here incidentally remark that the animals of Cyclotus, 

 Cyclo'pJioms, and Megalomastoma, three of the five genera of 

 the Family Gyclostomacea of Asiatic origin, represented in 

 America and the West Indies, have a buccal plate in addition 

 to the lingual membrane, (as to Bourciera and Hydrocena I 

 am not informed*), while in Cyclostom.us and Tudora of Afri- 

 can, and, I believe, in the genera of West Indian oi'igin, the 

 buccal plate is wanting.f 



Before describing the more remarkable features of the dis- 

 tribution of operculat^d shells in the West Indian sub-prc- 

 vinces, I may observe that a statement of the number alone of 

 genera represented in different parts of the American Conti- 

 nent and in the West Indies is comparatively of little value. 

 The annexed table gives the names of the genera, with the 

 number of species in each sub-province. The mark * indicates 

 that the genus is not represented on the Continent, and f that 

 the continental species do not exceed three in number. Gy- 

 clophorus and Schasicheila are the only genera with more 

 numerous continental than insular species, while Bourciera 

 and Hydrocena are exclusively continental. 



Seeing that four operculated species only are common to 

 the Continent and the Islands, the extraordinary fact appears 

 that the West Indian Islands have nearly 600 peculiar species 

 of operculated land shells. 



St. Croix (Porto Rico group) is the only island in which, so 

 far as I have ascertained, evidence has been discovered of 

 extinct operculated species. Gyclostoma hasicarinatum and G. 

 chordiferum, found with other sub-fossil species {Helix, Buli- 

 mus, and Pupa), have been described by Pfeiffbr. 



* Since putting this in the printer's hands, Prof. Theo. Gill has called 

 my attention to the fact, that Bourciera has been placed by Troschel 

 among the genera of Helicinacea, with which it essentially agrees in denti- 

 tion, while Hydrocena has been taken as the type of a pecuhar family also 

 related to Helicinacea, in which the buccal plate is absent. 



t See my paper "On the Buccal Plate in Certain Genera of the Family 

 Gyclostomacea," Amer. Jour, of Conch., i. 45, in which I refer to Troschel 

 " Gebiss der Schnecken," part i., 1856. ' 



