some new and peculiar Mollusca. 155 



Station 12, 1450 fms. ; a fragment only, but evidently- 

 belonging to this species, which I have described from speci- 

 mens taken in the ' Porcupine' and 'Challenger ' Expeditions. 

 ' Porcupine ' Expedition, 1869, off the west coast of Ireland, 

 1180-1476 fms. < Challenger ' Expedition, lat. 37° 26' N., 

 long. 45° 14' W., 1000 fms. 



The slit in D. subterfissuyn is on the under or ventral side 

 of the shell, being the same position as in the D. inversum of 

 Deshayes, and the reverse of that in his D. rubescens and in 

 D. ensiculus. The organization of the animal is unknown ; 

 but D. inversum may be the type of a distinct genus. 



A single and dead specimen of another shell, apparently 

 belonging to the genus Dentalium,^ occurred in Station 16, 

 1785 fathoms. It is narrowly cylindrical, rather solid, glossy, 

 smooth, and a quarter of an inch long. Its peculiarity con- 

 sists in the posterior termination forming a second and nar- 

 rower cylinder, which issues out of the larger and longer one, 

 as if from a sheath. This process has an entire and circular 

 point ; so that the shell cannot be a species of Siphodentalium. 

 I propose to name it Dentalium vagina. Perhaps two imper- 

 fect specimens of a Dentalium from Station 12, 1450 fathoms, 

 may belong to the same species. 



SiPHONODENTALIUM, M. Sars. 



In the ' Journal de Conchy liologie ' for 1874, p. 258, the 

 Marquis di Monterosato proposed the abbreviation of this ge- 

 neric name to Bipliodentalium ; and I agree with him that it 

 would be convenient. 



Sipliodentalium vitreum, M. Sars. 



Dentalium vitreum, M. Sars, Nyt Magaz. Naturvid. 1851, Bd. vi. p. 178 



(Siphpnodentalium, 1858). 

 D. lobatum, G. B. Sowerby, Jun., Thes. Conch. (1866), vol. iii. p. 



100, fig. 44. 



Body whitish, gelatinous, and nearly transparent : mantle 

 rather thick, forming a collar round the foot : tentacles thread- 

 like, very slender, and having oblong tips or bulbs ; they are 

 not numerous, but extensile and irregular in length, issuing 

 from underneath the edge of the mantle : foot cylindrical, ex- 

 tensile, and attaining a length equal to that of the shell ; when 

 at rest it is conical ; but the point fully stretched out expands 

 into a round and somewhat concave disk witli serrated or 

 notched edges : excretal fold or tail at the narrowest end of 

 the shell, tubular, and having the front split open and exposed 



11* 



