CYCLOSTOMA. 345 



GENUS CYCLOSTOMA, LAMARCK. 



GENERIC CHARACTERS. 



ANIMAL terrestrial, elongated, unisexual ; mouth at 

 the termination of a somewhat extensile proboscis ; ten- 

 tacles, two, subulate ; eyes at the external base of the 

 tentacles ; respiratory sac largely open in front and 

 above. 



SHELL discoidal, ovate conic, or pupoid, whorls cylin- 

 drical ; aperture circular, or slightly angular posteriorly ; 

 lip reflexed, its inner margin, and generally the outer 

 margin also, continuous ; operculum horny or bony, 

 the nucleus central, umbilicated, the spirals more or 

 less numerous. 



GEOGRAPHICAL DISTRIBUTION. This genus belongs to 

 the tropics, or to the temperate regions bordering there- 

 upon. In America, it ranges from Florida to Brazil. It 

 is found on all the borders of the Mediterranean, is want- 

 ing on the western coast of America, Western Africa, and 

 New Holland, is abundant in India and the islands of 

 the Indian Ocean, and on the equatorial groups of the 

 Pacific islands. 



REMARKS. The genus Cyclostoma was instituted by 

 Lamarck ; and he at first included in it various land, 

 VOL. n . 44 



