127 



ornamented mtli indistinct concentric wi*inkles from one fourth of a line 

 to two lines in width. There are probably fine concentratic stride, although 

 I have not, (owing to the partially exfoliated state of the specimens ex- 

 amined) been able to detect them. 



This species varies considerably in the amount of the convexity of the 

 dorsal valve and in the size of the mesial fold in front. Some have a wide 

 flat space in the umbonial region, and in such, on a side-view, the outline 

 of the shell rises from the beak at an angle of about 45° only, while in 

 others, which are more ventricose, this angle is full 60° with the plane of 

 the margin. 



Sometimes the sides are strongly compressed, so that the shell becomes 

 sub cylindrical and greatly produced in front, the length exceeding the 

 width. In some specimens the striae are nearly all of the same size, but 

 in general they alternate as in the finest marked specimens of jS. alternata 



Resembles S. Thalia, but that species has the ventral valve concave 

 nearly to the beak. It is more uniformly gibbous than C.fluctuosa. 



Locality and Formation. — Anticosti, Hudson River group. 



Collector. — J. Richardson. 



The following species are considered to be either new or closely allied 

 to some that are not very well known among American collections : — 



Strophomena Julia. (N. sp.) 



Fig. 105. 



Fig. 105. — Strophomena Julia. — a, Ventral view; 6, side view, enlarged two 

 diameters. 



Bescrijytion. — Shell small, transversely oblong, greatest width at the 

 hinge-line ; sides somewhat straight ; front angles obtusely rounded ; front 

 margin straight or gently convex. Ventral valve convex ; the front 

 margin and the anterior half of the sides abruptly curved down to form a 

 deflected border, the length of which is equal to one-third of the whole 

 length of the shell. The visceral disc, or all that part of the shell which 

 is not included in the deflected border, is gently convex, most elevated in 



