172 
INTRODUCTION 
Helix makes up less than one half, and BiiUmus about 
one third of the whole number, ffelieina,' a genus not 
numerically strong, is very predominant; and Cyclosto- 
ma is considerably numerous. ClausiUa appears in the 
list of M. Pfeifier, but it comprises only species which 
are not true Clausilice, and for which, more recently, he 
has constructed the genus Cylindrdla. 
The facts exhibited in the tables which we have given. 
and derived from the other sources mentioned, suggest 
certain general inferences concerning the geographical 
distribution of the genera which are worthy of notice, 
and deserving of being tested by observation in other 
parts of the world. They indicate, that native species 
of the European genera of the Llmacidce, namely, IA- 
max, Arion, and Testacella, are wanting in the tropical 
We have not seen that part of the work of M. De la Sagra, which 
[•eats of Helicina, but the monograph of this genus by Mr. Sowerby, (The- 
saurus Conchyliorum,) gives descriptions of seventy-two species, of which 
seventeen are set down as belonging to Cuba, fourteen to the Antilles and 
nt her West Indian islands, and thirteen more to the adjacent pans of the 
continent of America. Bolivia, on the western coast of South America, is 
said to furnish three species, and the Philippine islands six. A single 
cribed to Opara, in Polynesia : and to this we may add nine 
collected by the United States Exploring Expedition. The localities 
of the remaining species are unknown. We make a similar remark con- 
cerning Cyclostoma, the species of which Mr. Sowerby lias also eo 
into a monograph. Of one hundred and thirty-three species, whose habitat 
is known, thirty-two belong to the West Indian islands, forty-two tp the 
Indian Archipelago, thirteen to the African islands, five to Polynesia 
.. add nine from the Exploring Expedition,) four to the islands 
of the Mediterranean, seven to Europe, nine to Asia, eight to Africa, ami 
thirteen to America. Some of the species ascribed to tin itinents, pro- 
