150 ARCID^. 



and at depths ranging between that mark and 86 fa- 

 thoms. Glacial deposit, Paisley (Crosskey). Morch 

 and Walker have recorded it from Greenland, Asbjorn- 

 sen from Norway, Loven and Malm from Sweden, 

 M' Andrew from the Spanish coast and Algiers, and I 

 have found it in the Gulf of Genoa. Gould says that 

 the N. proximo, of Say (from the Massachusetts coast) 

 is closely allied to the present species, if not identical 

 with it ; but that shell seems to be less glossy, and the 

 shape rather more obliquely transverse. 



My note of the animal differs a little from Mr. Clark's 

 description, and is as follows : " Colour greyish-white. 

 Mantle finely fringed. Foot tongue-shaped, folded 

 up when at rest; when it is expanded, it assumes a 

 roundish-oval shape, and its margin is regularly den- 

 tate, or set with numerous point-like tentacles." The 

 shell is usually less solid than that of N. nucleus ; the 

 anterior slope is more abruptly truncate, and the pos- 

 terior slope more produced ; the umbonal area is more 

 convex and prominent; the beaks are more terminal; 

 and the polished epidermis will always serve to distin- 

 guish it from its dull congener. 



It is not the Area nitida of Brocchi, which is a species 

 of Leda. Weinkauff supposes that our shell may be the 

 young of N. sulcata ; but this idea is not correct, and I 

 fear that it may tend to throw some discredit on his list 

 of Algerian Mollusca, although it cannot be denied that 

 he has considerably extended our knowledge of this 

 branch of the North African fauna, and further results 

 may be expected from his zeal and opportunities. The 

 young of N. sulcata, instead of being smooth and glossy 

 like N. nitida, is remarkably rough, and of a dusky hue, 

 and it is a much broader and flatter shell. 



