[22] 





b 



o 



i 



< 





ci 





«% 



s 



3 





< 



'S 





J 



1 



s' 



«^ 



r 



1 







n 



£ 



3 



si 



J 





a 







S5 



s 



o 



o 



•-! 



a 



Oi 



O 



CQ 



Helix, 



64 



21 



23 



32 



42 



35 



36 



36 



19 



Bulimus, 



10 



21 



31 



9 



8 



10 



31 



28 



64 



Cylindrella, 



3 



13 



7 



2G 



20 



25 



5 



6 fraction. 



Thus it appears that Helix predominates in North America, 

 Bulimus in South America, and Cylindrella in the West In- 

 dies. The closer relations of the subprovinces, embracing 

 Cuba, Jamaica and Haiti with North America, and of the Porto 

 Rico and Guadeloupe subprovinces with South America, are 

 shown by the greater numerical representation of Helix in the 

 former, and of Bulimus m the latter. Bulimus has compara- 

 tively few species in North and Helix in South America, while 

 the specific development of those two genera are more nearly 

 balanced on the Continent, in Mexico and Central America, 

 and in the Islands, in the Porto Rico and Guadaloupe. sub- 

 provinces. The distribution of Cylindrella [o^ndi it is the same 

 with Oleacina and Spiraxis) shows that Cuba, Jamaica and 

 Plaiti are more closely allied to Mexico and Central America 

 than the Porto Rico and Guadeloupe subprovinces, in which, 

 as well as in South America, those three genera are compara- 

 tively feebly represented. 



In previous pages I referred the " origin " of genera to the 

 country in which there is the maximum specific representa- 

 tion, and presented a statement showing the genera, both oper- 

 culated and inoperculated, the origin of which might, on such 

 data, be assigned to the American Continent or the West In- 

 dian Islands. I remarked that the majority of the genera of 

 operculates common to the Continent and Islands have the 

 greater number of species on the Is'ands, but that the re- 

 verse is the case with the majority of such genera of inoper- 

 culates. 



Of the before- mentioned genera, represented both on the 

 Continent and Islands, those which appear to have a majority 

 of species in the latter are Achalina, Pupa, Macroceramus and 

 Cylindrella^ but in no sense can the two former be said to be 

 of West Indian origin. 



The generalizations to which I have referred are at least 

 interesting, but less satsfactory as to the inoperculates than 

 the operculates, if Pfeifl'er's classification be used, because, as 

 already observed, some at least of his generic terms embrace 

 very various forms, the geographical distribution of which 

 should be considered. 



Pfeifter includes in Bulimus and Achatina many species 

 now better known as of the genus Stenogyra^ and in Bulimus 



