CYLICHNA. 507 



loped, so as in many species to serve as swimming organs. 

 The foot is in some extremely small, in others a crawling 

 disk of considerable dimensions. 



There are more than one hundred and fifty species of this 

 family known. They inhabit all parts of the world, and 

 some of them are very widely diffused. The shelled forms 

 have lately been monographed, and a classification of the 

 animals and shells proposed by Mr. Arthur Adams, in the 

 "Thesaurus Conchyliorum" of Mr. G. B. Sowerby, jun. 



CYLICHNA. LovEN. 



Shell cylindrical, usually strong, smooth, striated, or 

 grooved, truncated or subtruncated at the spire, which is 

 in some species involute, in others slightly produced : aper- 

 ture contracted, slightly dilated below, pillar lip thickened, 

 with or without a fold. No operculum. 



Animal not investing the shell ; its head depressed, sub- 

 quadrate, truncate in front, produced posteriorly into two 

 more or less separated broad tentacula in front of whose 

 bases are the more or less distinct eyes ; lateral lobes 

 reflected more or less distinctly on the shell ; mantle with 

 a posteal process or lobe ; foot oblong, shorter than the 

 shell; tongue with a single row of subquadrate axile teeth, 

 with inflexed serrulated apices ; these are flanked on each 

 side by several uncinated laterals, the innermost ones much 

 larger than the others. No gizzard. 



