Branson — The Fauna of the Residuary Auburn Chert. 43 



PAKALLELODus OBLiQuus, 11. geii. and sp. 



PL vii. f. 9-10. 



Shell obliquely subovate, strongly convex, maximum 

 length observed forty millimeters, width half the length, 

 widest at posterior end of hinge. Hinge plate nearly 

 straight, about half the length of the shell. Beaks situ- 

 ated slightly in front of the middle of the hinge line. One 

 tooth anterior and one posterior to beaks in right valve ; 

 two teeth anterior and two posterior to beaks in left 

 valve. Teeth long, almost parallel to hinge line. The 

 anterior margin of the shell curves abruptly downward 

 from the hinge to the ventral margin, ventral margin 

 moderately and evenly convex, posterior margin passing 

 downward and backward in a nearly straight line to the 

 ventral margin. Umbones prominent, curving inward 

 over the hinge line. An umbonal ridge, prominent for 

 half the length of the shell, extends backward to the pos- 

 tero-ventral margin. Surface of shell marked with rather 

 coarse concentric striae, faintly impressed on casts. Mus- 

 cular scars not traceable on casts. 



This genus is characterized by its dentition and the 

 position of its hinge. The shell closely resembles that 

 of Whiteavesia in shape. 



Genus based on several specimens, two of which show 

 the dentition. Number 11534 of the invertebrate paleon- 

 tological collection of Walker Museum. 



CATAscHiSMA TYPA, n. geu. and sp. 



PI. vii. f. 15. 



Shell small, low, width and height subequal. Whorls 

 four, increasing rapidly in size, lower whorl ventricose. 

 Apical angle about ninety-five degrees. Umbilicus prob- 

 ably present. Lip with a shallow slit considerably below 

 the middle of the whorl. Band obscure, broad, slightly 

 depressed, entirely covered excepting on the lower whorl. 

 Lines of growth not apparent. The slit is not at the 

 summit of a ridge, the contour of the whorls being scarce- 

 ly modified by its presence. 



