17 



CnoNETES Canadensis. (N. sp.) 



Fig. 7. 



Fig. l.^Choneies Canadensis. A specimen of the long form. Specimens much broader 

 and shorter proportionally occur. The upper figure shows the area, that of the 

 ventral valve uppermost. 



Description. — Shell semi-circular or semi-olliptical, the proportional 

 length and width variable. Ventral valve gently convex, in general most 

 elevated at about one-third the length from the beak ; the cardinal angles 

 flattened or slightly concave ; umbo broadly depressed, convex ; beak 

 scarcely distinguishable from the cardinal edge. The area is rather 

 large, being about a line high at the beak ; nearly flat or very shghtly 

 concave, nearly smooth, no traces of crenulations ; inclining backwards at 

 an angle of about 45^ with the plane of the lateral margin. The foramen 

 is triangular, its width at the base nearly twice its height, extending 

 nearly to the beak. 



Dorsal valve gently concave, corresponding to the ventral valve, in its 

 curvature, so as to leave only a thin space between them. The area is 

 about one-third or one-half the size of that of the ventral valve,- and forms 

 nearly a right angle with the plane of the lateral margin. 



The surface is covered with very fine, obscure radiating stri9e,from ten 

 to fifteen in the width of two lines. Some specimens, also, exhibit a number 

 of concentric ridges or undulations of growth. Many show shallow, concave 

 furrows from half a line to one line wide, which radiate from near the 

 beak to the margin. These are most distinctly seen m specimens from 

 which the shell is either wholly or partially removed. In such cases 

 these furrows are either straight or shghtly curved, the convex side of 

 the curve being outwards, towards the sides. When the shell is a little 

 worn fine closely arranged punctures may be seen between the striaj. 

 When the shell is removed, the cast of the inner surface is sometimes 

 quite rugose with punctures and obscure irregular tubercles. Often, 

 however, the cast only exhibits the radiating strite. 



B 



