UNIVALVES DENTALIUM. 191 



DENTALIUM — Tooth oh Tusk-Shell. 



DESCRIPTION OF PLATE XXXIII. 



Fam. 1. Fif^. 1. D. aprinutn. Fam. 1. Fig. 4. D. elephantinum. 



Fani. 1. Fig. 2. D. striatum. Fam. 2. Fig. 6. D. politum. 



Fam. 1. Fig. 3. D, dentalis. Fam. 3. Fig. 5. D. entalis. 



Shell univiilvp, tubular, straight, or slightly curved, with an undi- 

 vided ravitif open at both ends. 



THE shells of this singular genus resemble an ele- 

 phant's tusk in miniature. The principal distinctions 

 are in magnitude, curvature, and the number of ribs and 

 grooves with which some of the species are marked. 



The species of the first family are distinguished by 

 longitudinal ribs, which in the D. elephantinum gene- 

 rally amount to ten. The D. striatum differs from the 

 D. elephantinum, iu having eight ribs, and the inter- 

 stices striated. 



The D. rectum, though nearly allied to the D. ele- 

 phantinum, is a straight shell, and therefore easily dis- 

 tinguished from it. 



The next family comprehends those which are striat- 

 ed annularly : of these may be mentioned the D. poli- 

 tum, which is finely pointed, solid, and often of a rosy 

 or pinkish color ; and the D. eburneum, which is gene- 

 rally an inch and a half long, of a reddish or pale yel- 

 low color, with the tip frequently tinged with orange or 

 pink. 



The shells of the third family are smooth, or cover- 

 ed with strise, so minute that they cannot be discovered 

 without the aid of a magnifying glass. The D. pellu- 



