106 



ANIMALIA MOLLUSCA. 



and narrowed by an enlargement of the straight edge and the 

 folds of the columella. 



GENUS II. CYPRJEA, Lin. Porcelain. 



Spire projecting but little ; aperture narrow and extending 

 from one extremity to the other; shell resembling the half of 

 an egg; the rounded part smooth and adorned with beautiful 

 colours ; the under side flattened. 



GENUS III. PURPURA, Brug. Purple. 



Shell oval and thick ; columella without folds ; provided 

 with a short canal bent to the left ; last whorl of the spire 

 very large ; aperture very wide. 



GENUS IV. CASSIS, Brug. Helmet. 



Shell flattened behind, or with a spire only slightly pro- 

 jecting; aperture narrow, long and terminated anteriorly by 

 a very short canal, emarginated and reflected to the rear; 

 columella indented and plicated. 



ACEPHALA. 



Mollusca without distinct head, whose mouth, having no 

 teeth, is -concealed under the mantle, and cannot be thrust 

 forward, so that the animal rather receives the nutritive mo- 

 lecules brought by the water than seizes them of its own 

 accord ; only the senses of touch and taste are certainly ascer- 

 tained to exist. This class includes almost all the bivalved 

 shells, a great number of the multi valves, and some without 

 shells. The mantle opens in various ways, sometimes before, 

 sometimes all round, and then again only upon one side; 

 the shell is closed by means of muscles specially destined for 

 that purpose; it opens by the action of an elastic ligament 



