106 



ANIMALIA MOLLUSCA. 



and narrowed by an enlargement of the straight edge and the 

 folds of the columella. 



Genus II. Cypr^ea, 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 



