lOS 



DENTALIUM. 



(Plate XXII. fig. 1.) 



Shell univalve, straight, or nearly so, subconical, 

 tubular, not chambered, open at both ends. 



The simple construction of the shells in this ge- 

 nus and the paucity of species render it unneces- 

 sary to offer any extended remarks on their distinc- 

 tive character. They are all more or less, as their 

 name expresses, like teeth or tusks, and are com- 

 pletely separated from the other tubular families by 

 being entirely without contortion, though some- 

 what curved. 



They are usually discovered partly buried in the 

 sand; and the animal, which has by some naturalists 

 been supposed perfectly free and unattached to his 

 liabitation, is seen to shrink deeply into it for pro- 

 tection from impending danger. The opinion, that 

 the Tercbclla possesses the power of disengaging 

 himself from his shell, has arisen probably from 

 the circumstance of there being no apex, hinge, or 

 visible depression to which the connecting muscle, 



