53 



for about one-third the length, and gradually curving into the posterior 

 side ; the latter broadly and uniformly rounded to the base. The ante- 

 rior side of the cast is nearly flat, gently concave, regularly cordiform in 

 outline. (Fig. 2a.) Beaks small, strongly incurved, almost in contact. 

 There appears to be a short straight hinge between the beaks, about an 

 inch in length, forming an angle of about 50^ or 60? with the general 

 plane of the flat anterior side. The edge of the anterior side, from the 

 beak along the umbo, is acutely rounded, but gradually becomes more 

 and more obtuse, as it approaches the base. 



The cast exhibits a few concentric grooves, indicating, perhaps, lamel- 

 lose rings (5f growth on the su face of the shell. 



Height, from beak to base, three inches ; width at about half the height 

 ^wenty lines depth of both valves, measured across the flat anterior side, 

 \fig. 2a) twenty-six lines. 



Locality and Formation. — Gasp^ : Gaspe Umestone, No. 8. 



Collector. — R, Bell. 



Mytilarca nitida. (N. sp.) 



Fig. 22. Fig. 23. 



Fig. 22. — Mytilarca nitida. Internal cast of left valve. 

 Fig. 23. — " " View of the anterior side. 



Description. — Cast of the interior ovate ; anterior side gently con 

 cave in the upper two-thirds, slightly convex below; posterior side 

 broadly and gently convex, a small portion next the beak, (indicating the 

 hinge-line) straight. Base nearly uniformly rounded. Umbones moder- 

 ately prominent, obscurely carinate or narrowly rounded. Beaks small, 

 closely incurved, almost in contact, slightly turned forwards. Between 

 the beaks there is a short straight hinge-line, which forms an angle of a 

 little less than 90? to the anterior side. The outline of the anterior side 



