UNIVALVES. — DENTALIUM. HI 



DENTALIUM.— Tooth or Tusk-Shell. 



Animal— a Terehella : Shell univalve, tuhular, straight, 

 or slightly ciirvedy with an undivided cavity open at both 

 ends. 



Of this singular genus there are but twenty-two species; 

 in their general form they are very similar, and represent 

 an excellent fac-simile of an elephant's tusk in miniature. 



The chief variations which they seem subject to are, 

 in magnitude, and in the number of ribs and grooves 

 that some of the species are supplied with; some trifling 

 distinction may also be made with regard to the de- 

 gree of curvature which many of them possess. One of 

 the largest and most valuable species is the D«italium 

 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 resembles 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 

 longerandnarrowerin proportion, and the larger aperture 

 is angular, whereas the smaller is very contracted and 

 round; besides, it is supplied with 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 

 straight instead of curved. It is, moreover, adorned \^ith 

 doubled, or tripled longitudinal strioe, which at the same 



