DENTALIUM TUSK SHELL. 127 



the 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, 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. The head is 

 furnished with jaws, and lips bearing teeth. 



