144 UNI VA LVES DENTALIUM. 



gree of curvature wliicli many of tliem possess. One of 

 the largest and most valuable species is the Dentalium 

 elephantinum or elephant's tusk, it is often three or 

 four inches long, is slightly curved, has generally ten 

 strong elevated ribs, which are encircled by dark green 

 bands on a greenish ground ; it inhabits the Indian and 

 European seas. 



The Dentalium aprinum very much resemt)les the 

 last, but it is usually much smaller and perfectly white. 



The Dentalium striatulum or striated tooth-shell also 

 resembles the Dentalium elephantinum, but it is much 

 longer and narrower in proportion, and the larger aperture 

 is angular, whereas the smaller is very contracted and 

 round; besides, it is supplied w ith eight ribs and eight 

 striae; and it is more uniformly green than the elephan- 

 tinum. 



The Dentalium rectum, though nearly allied to the 

 elephantinum, is easily distinguished from it by its being 

 sti-aight instead of curved. It is, moreover, adorned with 

 doubled, or tripled longitudinal striae, which at the same 

 time are encircled w ith annular ones. The Dentalium 

 fasciatum is a small species, finely striate, and is encircled 

 with four or five brown bands on a greyish ground. 



The next division of the Dentalia comprehends those 

 which are striate annularly instead of longitudinally, and 

 those which are scarcely striate at all, at least so imper- 

 ceptibly as to demand the aid of a glass to prove whether 

 they are in reality striate or perfectly smooth, so even 

 and polished is their surface. 



Those species which answer to this description are the 

 Dentalium politum or polished tooth-shell, which is fine- 

 ly pointed, solid, and often of a rosy or pinkish color, 

 the Dentalium eburneum or ivory tusk, and the Den- 



