Wetter — Kinderhook Faunal Studies. 89 



anterior extremity of the hinge-line in front, and posteriorly 

 curving into the somewhat abruptly rounded posterior margin ; 

 dorsal margin gently curved to the extremity of the hinge- 

 line. Beaks acute, suberect, situated at the extreme anterior 

 end of the shell. Valves moderately convex in the posterior 

 part, becoming gibbous anteriorly. The line of greatest 

 convexity near the ventral side of the shell, the ventral slope 

 being very steep and the dorsal slope more gentle. Surface 

 marked by fine radiating striae, and by more or less incon- 

 spicuous lines of growth. 



Remarks. This species differs from the last in the pres- 

 ence of the radiating striae and in the more ventral position 

 of the line of greatest convexity. 



GONIOPHORA JENNAE (Win.). 



PL III. f. 13-14. 



Isocardia jennae. Bull U. S. G. S. No. 153: 314. 



The specimens of this species in the University of Michigan 

 collection labled " types (in part) " are three in number, but 

 the specimen from which Winchell took the measurements 

 given in his original description, is missing, none of those 

 observed being as large as that one. The largest and best of 

 the specimens studied will therefore be selected as the type. 



Shell very oblique, the beak at or near the anterior 

 extremity. Dimensions, 26 mm. from the beak to the pos- 

 terior basal angle, hinge line 14 mm. in length, greatest 

 width from the posterior extremity of the hinge-line to the 

 middle of the ventral margin 14 mm. Hinge-line straight. 

 The posterior margin truncated, meeting the hinge-line in an 

 obtuse angle. The postero-ventral extremity of the shell 

 acutely angular ; the ventral margin nearly straight through 

 the greater part of its length, curving upward anteriorly to 

 meet the hinge-line under the beak. The umbonal ridge 

 elevated and sharply angular, slightly sigmoidal from the beak 

 to the posterior basal angle. The postero-dorsal slope from 

 the umbonal ridge concave, becoming more and more steep 

 anteriorly until at or near the beak it faces dorsally, and is 

 overhung by the umbonal ridge; the antero-ventral slope 

 steeper than the opposite one posteriorly, but more gentle 



