FAMILY CYCLOSTOMACEA. 175 



of an inch in length, of which the operculum is horny and of fewer 

 whorls than the shell. One or two other species have been de- 

 scribed on the Continent, but their specific value is a little doubtful. 

 The genus is not known out of Europe. 



The British genera of Cyclostomacea are : — 



1. Cyclostoma. Animal carrying an ovately turbinated solid 



shell of five whorls. Operculum shelly. 



2. Acme. Animal carrying a minute turriculate glassy shell of 



six whorls. Operculum horny. 



Cyclostoma elegans. 



Genus I. CYCLOSTOMA, Lamarck. 



Animal ; oblong, carrying an ovate tubularly turbinated shell, 

 mantle free, head produced into a prominent ringed proboscis, 

 tentacles slender, wrinkled, with the eyes on superficial swell- 

 ings at their outer base, foot large and bilobed in front, short 

 behind, bearing an operculum. 



Shell ; ovately turbinated, of five rather solid tubular whorls, 

 having a nearly circular aperture. Operculum calcareous, 

 spiral, smooth. 



This conspicuously proboscis-snouted mollusk is the solitary re- 

 presentative in Britain of a group inhabiting in great abundance 

 the islands of the West Indies. According to the generally re- 

 ceived subdivision of the numerous foreign species of this family, 

 founded on the characters of the operculum, it is associated with a 

 number of globosely turbinated forms of larger size, peculiar to 

 Madagascar and the adjacent islands ; but takmg the generality of 

 its characters into consideration, it has a more direct affinity with 

 the West Indian and Central American Cyclostomacea, arranged 



