GASTEROPODA 



175 



Fig. 101. Lingual teeth of Cyclophorus.* 



The sexes are distinct ; the shell is spiral, and closed by an operculum, 

 presenting many beautiful modifications of structure, characteristic of the 

 smaller groups, which are often peculiar to limited regions, as in the HeliddcE, 

 The oldest fossil species are found in the Eocene Tertiary. 



FAMILY VI. CYCLOSTOMID/E. 



Shell spiral, rarely much elongated, often depressed, spirally striated; 

 aperture nearly circular ; peristome simple. Operculum distinctly spiral. 



Animal with the eyes on slight prominences at the outer bases of the 

 tentacles ; tentacles contractile only ; foot rather elongated. 



CYCLOSTOMA, Lamarck. 



Etym. Cyclos circle, stoma mouth. Type, C. elegans, PI. XII. fig. 40. 



Syn. Leonia (mammillaris) and Lithidion, Gray. 



Shell turbinated, thin, axis perforated ; aperture oval ; peristome conti- 

 nuous, simple, straight or expanded ; epidermis very thin. Operculum shelly, 

 pauci-spiral. 



Animal with clavate tentacles ; sole of the foot divided by a longitudinal 

 groove, the sides moved alternately in walking ; the end of the long muzzle is 

 also frequently applied, as by the looping-snails (Truncatellae), and used to 

 assist in climbing. 



Fig. 102. Cyclostoma elegans, from Charlton, Kent. 

 Distr. Above 80 sp. S. Europe ; Africa, Madagascar. The only British 



* C. aquilum, Sby. (original). From a specimen gathered by J. W. Laidlay, Esq. 

 on the steps of the great idol-temple of Maulmein, Birmah. 



