172 INTRODUCTION. 



Selix makes up less than one half, and Bidimus about 

 one third of the whole number. Selicina,^ a genus not 

 numericallj strong, is very predominant ; and Cydosto- 

 ma is considerably numerous. Clausilia appears in the 

 list of M. Pfeiffer, but it comprises only species which 

 are not true Clausilice, and for which, more recently, he 

 has constructed the genus Cylvndrella. 



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 Limacidce, namely, Li- 

 max, Avion, and Testaeella, are wanting hi the tropical 



' We have not seen that part of the work of M. De la Sagra, which 

 treats of Helicina, but the monograph of this genus by Mr. Sowerby, ( The- 

 saurus Conchy liorum,) gives descriptions of seventy-two species, of which 

 seventeen are set down as belonging to Cuba, fourteen to the Antilles and 

 other West Indian islands, and tliirteen more to the adjacent parts 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 

 species is ascribed to Opara, in Polynesia : and to this we may add nine 

 others, collected by the United States Exploring Expedition. The locahties 

 of the remaining species are unknown. We make a similar remark con- 

 cernmg Cyclostoma, the species of wliich Mr. Sowerby has also collected 

 into a monograph. Of one hundred and thirty-three species, whose habitat 

 is known, thirty-two belong to the West Indian islands, forty-two to the 

 East Indian Archipelago, thirteen to the African islands, five to Polynesia, 

 (to which we add nine from the Exploring Expedition,) four to the islands 

 of the Mediterranean, seven to Europe, nine to Asia, eight to Africa, and 

 thurteen to America. Some of the species ascribed to the continents, pro- 

 bably only occur upon the islands adjacent. 



