GASTEROPODA. 



157 



head, but neither eyes nor tentacula ; foot a pointed cone ; 

 stomach with a gizzard ; tongue broad, oval, with a row 

 of axile quadrate teeth; on each side a simple row of 

 hooks having folds at the edge. — 30 species; also fossil. 



These shells resemble in form an elephant's tusk ; some 

 species are ribbed, or fluted longitudinally, others trans- 

 versely, but many are smooth. They are found in the 

 Indian and European seas; of the latter there are two 

 species — D. entalis, found on the northern shores of Eng- 

 land, and D. Tarentum, on the southern. The animal is 

 said to feed on small bivalves and Foraminifera. 



Cadultjs. Phil. — Shell distinguished from Dentalium 

 by its being short, completely oval, with the aperture 

 almost circular, of which the back part is somewhat smaller, 

 and the edge is notched. — 1 species, fossil. 



Philippi formed this genus for a fossil, D. ovulurn. 



Order V. 

 TECTIBKANCHIATA. 



The animals have the organs of breathing unsymmetrical ; 

 more or less covered by the mantle. The shell sometimes 

 completely encloses the animal, at others it is rudimentary 

 and internal ; seldom absent. 



Family 1 . — PEE UR OB RAN CUE A. 



The gills of these animals are situated under the edge 

 of the mantle. — Marine. 



Umbrella. Lam. — (Umbraculum Schum. ; Gastro- 

 plax Plain.; Acardo Megerle.) — Shell rather irregular, 



