CHITONID.E. 113 



Shell spiral.* 



Shell snail-shaped. 

 Aperture very wide : 

 Outer lip slit or perforated . Haliotidae. 



Outer lip entire Naticada. 



Aperture moderate : 



Interior pearly Trochidte. 



Interior not pearly .... Littorinada. 

 Shell lengthened : 



Aperture channelled .... Cerithiadce. 

 Aperture simple : 



Operculum spiral Turritelladae. 



Operculum of successively en- 

 larging plates Pyramifelfada. 



163 



FAMILY I. CHITONID^:. 



Shell formed of eight transverse plates, lodged 

 in a leathery mantle, which overlaps the body on 

 all sides. Animal with a broad, oval foot ; no 

 eyes or tentacles ; tongue long, narrow, with three 

 series of teeth. 



Chiton (Linn.) . Coat-of-mail Shell. Shell-plates 

 wider than long, overlapping. 



C. albus. C. fascicularis. 



asellus. Hanleyi. 



cancellatus. Isevis. 



cinereus. Fig. 362;^. s. marmoreus. 



discrepans, ruber. 



* Coecum (fig. 184) in the Turritelladcc is tubular, resembling 

 Dentalium. 



