CHITONID^. 113 



Shell spiral."^ 



Shell snail-shajDed, 

 Aperture very wide : 

 Outer lip slit or perforated . Haliotida. 



Outer lip entire Naticadfje, 



Aperture moderate : 



Interior pearly Trodiidm. 



Interior not pearly .... Littorinada. 

 Shell lengthened : 

 Aperture channelled .... Cerithiadce. 

 Aperture simple : 



Operculum spiral TiirritelladcB. 



Oj)erculum of successively en- 

 larging j)lates Tymmidellad(B. 



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. laevis. 



cinereus. Fig. 1 62 ; n. s. marmoreus. 



discrepans. ruber. 



* Ccecum {fig. 184) in the Turritelladce is tubular, resembling 

 Dentalium. 



