OP CONCIIOLOOY. 349 



REMARKS ON THE DISTRIBUTION" OF THE INOPER- 

 CULATED LAND SHELLS WHICH INHABIT 

 THE CONTINENT OF AMERICA AND 

 THE WEST INDIES. 



("In continuation of Papers pp. 5-1 — 58 and 136 — 143.) 

 BY THOMAS BLAND. 



In previous Papers my remarks were confined chiefly to 

 the opercnlated land shells of the American Continent and 

 the West Indies, but I propose now briefly to discuss the sub- 

 ject of the distribution of the inoperculates. 

 ^ i Pfeiffer [Mon. Hel. Viv.) divides them (exclusive of Proser- 

 pinaced) into 31 genera, and describes over 5000 species, — to 

 the present date the number known and described may be es- 

 timated at, but probably exceeds, 5500. Without assuming 

 absolute correctness, it may be stated, that while the Ameri- 

 can Continent has 10 per cent, and the West Indies 39 per 

 cent, of the operculates, the former has about 23 per cent, and 

 the latter about 14 per cent, of the inoperculates. 



According to Pfeiffer's classification, the following genera 

 are represented, both on the Continent and Islands, viz: Helix, 

 Streptaxis, Bulimus, Spiraxis, Orthalicus, Achatina, Oleacina, 

 Tornatellina, Pupa, Macroceramus, Cylindrella, Balea, Glausilia, 

 Vitrina, Simpulopsis and Succinea. Considering, however, the 

 great number of different forms embraced in several of those 

 genera, it is not possible, with the use of such generic terms 

 alone, to give a satisfactory view of the special relations of 

 the continental and insular faunas. 



Looking, however, at the relative extent to which each of 

 the above-mentioned genera are specifically represented in 

 different portions of the Continent, as well as in each of the 

 West Indian sub-provinces, evidence is afforded of the general 

 relationship of the faunas of the sub-provinces inter se, and 

 with the Continent. 



Taking, for instance, the number of inoperculated species in 

 the subprovinces and sections of the Continent, the following 

 are approximately the proportions (per cent.) in which Helix, 

 Bulimus and Cylindrella are represented in each : — 



