54 G. O. Sars. 



Seen laterally (fig. 3 a), the shell exhibits a pronounced 

 clavate form, being much higher in front than behind, with the 

 greatest height equalling about half the length. The anterior 

 extremity is broadly rounded, whereas the posterior one 

 appears somewhat obliquely truncated, with the lower corner 

 more prominent than the upper. The dorsal margin has its 

 greatest curvature just above the eye, where it exhibits an 

 almost angular bend, and from thence slopes evenly, and at 

 a nearly straight course, to the hind extremity. The ven- 

 tral margin is deeply sinuated somewhat behind the middle, 

 and joins the posterior edge by an abrupt curve. 



Seen from above (fig. 3 b), the shell appears very tumid, 

 the greatest breadth, which occurs considerably behind the 

 middle, fully equalling the height. It exhibits a rather 

 regular ovate form, with the side-contours evenly curved, 

 and the anterior extremity somewhat more pointed than the 

 posterior. 



The valves are very unequal, the left one being much 

 larger than the right, and overlapping it considerably along 

 the whole anterior extremity, as also posteriorly. The inner 

 duplicatures are not particularly broad. 



The surface of the shell is of a dull appearance, and 

 often covered with muddy particles. It appears closely 

 granular all over, exhibiting, as it were, a squamous 

 sculpture. Moreover, a number of well-defined obtuse tubercles 

 may be traced on each valve,- being more conspicuous 

 towards each extremity. Both anteriorly and posteriorly 

 the shell is densely hairy. 



The colour of the shell, in living specimens, is a rather 

 uniform yellowish green. 



The several appendages agree on the whole in their 

 structure rather closely with those in the typical species of 



