186 Trans. Acad. Set. of St. Louis. 



upon itself so that the hinge is nearly opposite the center of 

 the back of the shell ; hinge- line shorter than the width of 

 the shell ; cardinal extremities produced into small angular 

 ears." 



** Surface marked by strong radiating costae which bifur- 

 cate upon the umbo and below, and sometimes coalesce to- 

 wards the base of the shell, entire surface covered by fine 

 undulating concentric striae, and, in the upper part, by a few 

 strong wrinkles which are conspicuous on the ears and umbo. 

 A few marks of the bases of spines are noticed, but they 

 appear to have been irregularly distributed, and in our 

 specimen do not appear at all. Dorsal valve and interior 

 unknown." 



Dimensions of an average example : length 19 mm., breadth 

 19 mm., and convexity of pedicle valve 15 mm. 



Remarks. This species has been variously placed at dif- 

 ferent times in the genera Productus and Productella, but 

 there seem to be no grounds for removing it from the first 

 of these genera. It is a well defined Productus of the 

 seniirelioulatus type. It resembles P. burlingtoneusis H., but 

 is always a smaller shell and never has any indication of a 

 median sinus. The brachial valve is flattened toward the 

 cardinal extremities, and gently concave in the posterior 

 m«^dian portion, but bends upward rather abruptly toward 

 the lateral and anterior margins. 



Athyris crassicardinalis White. 



PL XVI. f. 18-24. 



Shell small, breadth a little greater than the length, the 

 greatest bivadth posterior to the middle, more or less broadly 

 pointed posteriorly. Pedicle valve most convex, the greatest 

 convexity posterior to the middle, elevated along the median 

 line ; the delthyrium large, open in all the specimens observed ; 

 the hinge-teeth large and strong, pointing obliquely inward 

 and toward the brachial valve. Brachial valve flattened trans- 

 versely, more or less strongly arched longitudinally ; the 

 umbo rather prominent, with the shell flattened on each side ; 

 the cardinal process notched in front, large and platform-like, 

 slightly excavated on top. Surface of shell marked by sev- 



