of West India Land Shells. 345 



in those to the east and south. These facts show, the distribu- 

 tion of species being considered, a result simihir to that arrived 

 at with regard to the distribution of genera, viz. that the 

 islands west of Portorico are more related to the N. American, 

 and those east and south to the S. American continent — Porto- 

 rico (with Yieqne) being connected with both. It is also 

 noticeable (Table I.) that the species of N. American generic 

 tjpe which are represented in the islands west, and also east 

 and south of Portorico, are generally more numerous in the 

 former, and those of S. American character in the latter. 



Only one operculate species, Ilellcma subglobulosa Poey, is 

 common to the American continents and the islands. "With 

 that exception all the operculated species inhabiting the islands 

 "VY. of Portorico (exclusive of Truncatella*) are peculiar to 

 those which they respectively inhabit, while six found in Porto- 

 rico and Yieque occur in the islands to the eastward. 



The following is the number of species in the islands: — 



576 380 



Portorico and Vieque ... 80 . . 30 



Islands E. and S. of Vieque . . 183 . . 50 



The large proportion of operculate species in the islands W. 

 of Portorico, and the diminution of them in that island, and 

 the islands E. and S. of it, is very remarkable. The relative 

 proportion of operculate and inoperculate species prevailing on 

 the continents is shown in Table I. The species common to 



* I omit Truncatella in Table IT., having, as I consider, insufficient data as to 

 the distribution of the species, ■which are, however, included in the Catalogue. 



