Branson—The Fauna of the Residuary Auburn Chert. 43 
PARALLELODUS OBLIQUUS, n. gen. and sp. 
Pl. vu. 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, Nn. gen. and sp. 
Pl. vu. 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. 
