58 G- O. Sars. 



Seen laterally (fig. 4 a), the shell exhibits a very regular 

 oblong, or rather elliptical form, with the greatest height 

 attaining not nearly half the length. Both extremities appear 

 evenly rounded and nearly equal. The dorsal margin is but 

 very slightly convex, without forming any trace of angle at 

 the junction with the anterior and posterior edges. The 

 ventral margin appears almost perfectly straight, the usual 

 median sinus being quite obsolete. 



Seen from above (fig. 4 b), the shell appears very much 

 compressed, the greatest width scarcely exceeding 1 /b of the 

 length. Its form is very narrow oblong, with the side- 

 contours but slightly convex, and the anterior extremity 

 somewhat more pointed than the posterior. 



The valves, at first sight, appear nearly equal. On 

 a closer examination, however, the left valve, as in the other 

 species, is found to be in reality a little larger than the 

 right, overlapping it anteriorly by a very narrow hyaline 

 rim. The inner duplicatures, especially the anterior ones, 

 are very broad and shelf-like, and their defining edge may 

 be pretty well traced through the shell. 



The surface of the shell is indistinctly striated longi- 

 tudinally, the striæ being very delicate, and in some cases 

 only with great difficulty traceable. At both extremities it 

 is clothed with delicate hairs, which on the posterior extre- 

 mity are particularly long and far apart. 



The colour of the shell in living specimens is trans- 

 parent yellowish, allowing the cæcal appendages of the 

 intestine and the opaque whitish ovarial tubes to be seen 

 through rather distinctly. At each extremity it is tinged 

 with deep green, this colour being especially very conspi- 

 cuous anteriorly, where it occupies a rather broad, semilunar 

 area inside the edge. 



