of West India Zand Shells. 



17 



posed another, Diplopoma, which is peculiar to Cuba. Bour- 

 ciera and Hydrocena, represented on the southern continent, do 

 not inhabit the islands. The following table displays the dis- 

 tribution of the insular genera. 





North 



South 



Forth 



Islands 





Islands 





America. 



America. 



and South 

 America. 



West of 

 Portorico. 



Portorico. 



E. and S, of 

 Portorico. 



Geomelania 









^ 





.... 



Truncatella 















* 

 * 



Cyclotus 



* 







^ 



* 



* 



* 



Cyclophorus. 









* 





.... 



* 



Megalomastoma 











* 



* 



* 



Jamaicia 









.... 



^ 



.... 



.... 



Licina 











^ 





.... 



Choanopoma 









.... 



* 



* 



* 



Ctenopoma 

















Adamsiella 



..*.. 









* 





.... 



Cyclostomus 















* 



Tudora 









.... 



* 

 * 



.... 



Diplopoma 



^ 



Cistula 









^ 



=^ 



l" 



* 



Chondropoma 









* 



* 



* 



* 



Stoastoma 











^ 



H: 





Troehatella 











^ 





.... 



Lucidella 











^ 



.... 



.... 



Helicina 









>j: 



9K 



* 



^ 



Sehasicheila 



^ 









^ 







Alcadia... 













^ 



.... 



. 











As regards the operculate shells the generic connexion of the 

 islands west of Portorico seems to be greatest with the northern 

 continent, and of those east and south with South America, 

 while Portorico holds an intermediate position. The richness 

 of the West India Islands in operculate genera peculiar to 

 themselves, is Yerj remarkable. The relative number of spe- 

 cies to genera on the continents and islands, as with the inoper- 

 culate shells, is also noticeable. 



The existence in Opara, one of the Polynesian Islands, of the 

 only species of Stoastoma* found elsewhere than in the West 

 Indies is the more curious, seeing that A. octona inhabits that 



* S. succineu7n Sowh. of Opara differs considerably from the species of the "West 

 Indies. Gray separates it from the others, under the subgeneric name of Elec- 

 trina. The shell is smooth, not spirally costate. 



