DENTALIUM TUSK SHELL. 127 



tbe Dentalium ; some naturalists have supposed 

 it to be free, and independent of its shell, but 

 later observations have led to the discovery of 

 the muscle by which it is attached to its abode, 

 into which it has been observed to shrink deeply 

 for protection from approaching danger. 



These shells are found principally on sandy 

 shores, sunk more or less deeply in the ground, 

 and placed in a vertical position. 



DENTALIUM Entalis. 



COMMON TOOTH SHELL. 



Specific- Character. Shell slightly curved, 

 slender, tapering, smooth, glossy, sometimes 

 marked with a few circular wrinkles or annu- 

 lations, colour white or yellowish, length an 

 inch and a half ; diameter at the larger end two 

 tenths of an inch, and one fourth as much at 

 the smaller end. 



It is commonly found on our coasts, particu- 

 larly those of the west of England. The animal 

 is very muscular, its shape is like its conical 

 shell, it has a mantle with a fleshy collar 

 through which it can protrude its head and foot. 

 Tne head is furnished with jaws, and lips bearing 

 teeth. 



