DENTALIUM TOOTH SHELL. 125 



derived from the Latin dens, a tooth, refers to this 

 form. There are but few species, and these 

 vary principally in external appearance, in mag- 

 nitude, in the degree of curvature, and in the 

 ribs or grooves with which some of them are 

 ornamented. One of the largest, called Denta- 

 lium Elephantinum is often three or four inches 

 long, and is strongly marked with longitudinal 

 elevated ribs. One species is so minute that it 

 is scarcely discernible by the naked eye, and re- 

 sembles a small bristle. 



There is but little known of the inhabitant ot 

 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, 

 and the inhabitant has been observed to shrink 

 deeply into it 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 Entails. 

 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 



