188 



CYCLOSTOMA. 



helix volvulus. — Muller. 



EncycU Meth. plate AQ\jjig. 3, a. b. 



Chemnitz, 9, table 123, jig. 1064, 1066. 



This genus, (of which the Turbo carinatus of Gmelin 

 is a species), is terrestrial ; and, from the great variety of 

 form in its different species, has been blended by for- 

 mer authors on conchology with other genera. It now 

 however only comprehends a branch of the Linnaean 

 G. Helix, from the others of which it essentially differs, 

 and is easily distinguished by the aperture being invari- 

 ably circular, and the margin thin, sharp, and outwardly 

 reflected at right augles with it. The G . Cyclostoma is 

 not the only one in which the species possess a circular 

 aperture: the G. Scalaria, Delphinula, and Paludina, 

 have it also: the two former have likewise a reflected 

 lip; but the annular processes of the one, and the pear- 

 ly substance of the other, distinguish and prove them 

 to be marine; while the G. Paludina, not possessing the 

 reflected lip, but a smooth sharp margin, is evidently a 

 fluviatile shell. These shells vary considerably in form, 

 some being tun etcd, some cylindrical, others flat at the 



