200 MALACOZOA. GASTEROPODA. CIRROBRANCHIATA. 



animal corresponding with the convexity of the shell; 

 mantle attached posteriorly to the origin of the foot, free 

 and thickened anteriorly by a circular muscle capable of 

 closing the shell, and through the centre of which is 

 protruded the foot, which is elongated, subcylindrical, 

 with a conical protuberance in the middle of its anterior 

 corolliform extremity ; the head indistinct, situated about 

 a third up, composed chiefly of a mouth having two in- 

 ternal horny spherical jaws, and two lips, each with three 

 pairs of labial tentacula ; oesophagus short, stomach 

 pyriform, containing a complex dental apparatus ; intes- 

 tine straight, slender, terminating at the posterior ex- 

 tremity of the body ; branchise two, symmetrically 

 disposed on the upper and lateral parts of the neck, and 

 composed of numerous tentacular filaments. 



Shell much elongated, conical, slightly curved, open 

 at both ends with circular apertures. 



1. Dentalium Entalis. Common Tooth-Shell. 



Shell tubular, elongated-conical, slightly curved, tapering 

 almost to a point, but truncate at the tip, and having a small 

 slit in the margin of its posterior aperture on the dorsal side ; 

 the surface glossy, nearly smooth, being obsoletely longitu- 

 dinally and transversely striulate ; the colour white. Length 

 two inches, breadth nearly two-twelfths. 



Although placed by M. Deshayes in the section including the 

 species which have the tip not slit, this, when perfect, always 

 has a small fissure at the end. This error has of course arisen 

 from the very rare occurrence of entire shells. Of twenty of 

 the best specimens which 1 could obtain only five have the 

 slender extremity complete. 



Abundant in deep water off Aberdeen, Boddam, Peterhead, 

 and Cruden, and very frequently brought up by the lines, 

 seldom with the animal, but often containing a siphunculus. 



Dentalium Entalis. Linn. Syst. Nat. i. 1263. Dentalium En- 

 talis. Penn. Brit Zool. iv. 145. PI. 90. f. 154. Dentalium En- 

 tails. Lamk. Syst. v. 345. Dentalium Entalis. Mont. Test. Brit. 

 494. 



