112 GASTROPODA. 



FAMILY IV. TORNATELLADJS. 



Shell external, solid, distinctly spiral, with a 

 narrow aperture, and a plaited pillar. Animal 

 with a broad flattened head, and broad tentacles ; 

 foot large, carrying an operculum. 



Tornatella (Lamk.). Shell ovate, with a conical 

 spire of many whorls ; aperture rounded in front. 

 Animal white ; head notched. 



T. fasciata. Fig. 161; n.s. 



Order II. PROSO-BRANCHIATA. 



Shell ample, usually capable of concealing the 

 whole animal ; mantle forming a vaulted chamber 

 over the back, in which the gills are lodged ; 

 gills comb-shaped or feather-shaped, in front of 

 the heart. Sexes distinct. 



Shell with the front margin entire Holostomata. 

 Shell with front margin notched or 

 produced into a canal .... Siphonostomata. 



TRIBE I. HOLOSTOMATA. 



Shell variously shaped ; margin of the aperture 

 entire ; operculum usually spiral. Animal with 

 a short muzzle, not retractile ; breathing-siphon 

 wanting, or formed by a lobe of the neck ; neck 

 and sides frequently adorned with appendages.* 

 Shell composed of eight plates . Chitonid<#. 



Shell tubular Dentaliada. 



Shell a low cone. 

 Shell entire: 



Summit turned forwards . . Patellada. 

 Summit backwards .... C'llyptrfeadce. 

 Shell slit or perforated .... Fissurellada. 



* Aporrhais, which by the preponderance of its characters 

 belongs to this tribe, has a canal. Natica and Scalaria have a 

 retractile proboscis. (Woodward.) 



