48 G. o. sars. [No. 8. 



posteriorlv there is a distinct nearly right-angled corner, mar- 

 king off the dorsal from the posterior edge. The ventral margin 

 is deeply sinuated in the middle and joins the anterior and pos- 

 terior edges by an even curve. Seen from above (fig. 6) the 

 shell exhibits a rather narrow oblong form, the greatest width 

 lying behind the middle and about equalling I of the length. 

 The lateral contours are but very slightly curved in the middle, 

 uearly parallel, but from the region of the eye they rapidly 

 converge anteriorly to a sharp point, whereas posteriorly they 

 are more evenly curved and meet in an obtuse point. 



The shell of the adult male (fig 7) exhibits a somewhat 

 more narrow shape, the height exceeding but little the half length. 

 The anterior extremity too is shorter and more abruptly rounded 

 than in the female, and the ventral margin less deeply sinuated. 

 Seen from above (fig. S) it appears somewhat more compressed 

 and the anterior extremity exhibits a peculiar swelling of its 

 marginal part, giving it the appearance of being narrowly trun- 

 cate at the tip. 



The shell is, especially in the female, of a very firm consis- 

 tency and its surface of a rather dull appearance, beintr every- 

 where closely set with numerous deep, rounded pits. Dorsally 

 it exhibits on either side, a little in front of the middle, two 

 irregular transverse impressions; but of any lateral protuberan- 

 ces there is no trace to be found either in the female or male. 



The valves are nearly equal, fitting exactly together at 

 either extremity; but dorsally, just above the eye, the right valve 

 overlaps to a short extent the left, forming the above mention^ 

 angular projection. The anterior edges of the valves, and i" 

 the female also the posterior, exhibit, besides a dense fringe of 

 very fine hairs, a closely set series of extremely small spinules 

 only visible by the aid of a high magnifying power. Moreover 

 in the female, some few coarser spines or spiniform processes 

 are found along the posterior edges (see PI. VI, fig. 0- In tllP 

 male (see fig. 11) this peculiarity occurs, that the anterior series 

 of spinules are indexed and surpassed by a very thin and 

 lucid border not occurring in the female.' The inner duplk» tl,rPS 



