OF DENISON UNIVERSITY. 
31 
Straight, passing by an abrubt curve into the posterior side, more slowly 
curving to the front ; greatest convexity above the middle ; umbo 
prominent, projecting; beak small, close to the hinge, situated about 
one-fourth from the front ; surface with fine concentric striae and deep 
equi-distant grooves about fourteen of which occur on a large specimen • 
hinge with a strong posterior tooth. 
Moot’s run, seventy feet below congl. I. 
SPHENOTUS CONTRACTUS, W. W. 
(See Vol. Ill, p. 69.) 
Winchell in 1865 identified this species with his own Edmondia 
bicarinata. Originally this species was supposed to have come from 
the equivalent of the mill-stone grit. Cf. also Cypricardia securis 
Win. Proc. Acad. Phila. 1870, p. 255. 
Genus Spathella. H. 
“Shell equivalve, inequilateral, wider behind, transversely sub- 
cylindrical. Anterior end short, narrowly rounded. Beaks sub-anter- 
ior, small. Umbonal slope rounded or sub-angular. Surface marked 
by concentric striae, which are often more or less lamellose. Interior 
unknown.” 
iSPATHELLA VENTRICOSA, W. and W. ? . 
(Plate IV, Fig. 20.) 
Our specimens do not fully agree with the figures of “Orthonota 
ventricosa,” but there seems to be a considerable range of variation, and 
as that species occurs in the Kinderhook group of Illinois, it seems 
likely that ours is closely allied if not identical. 
Freestone of middle Waverly. 
MYTILARCA FIBRISTRIATUS, W. and W. 
(Plate IV, Fig. 21, j 
The original description reads as follows : 
“Shell elongate oval, alternate at the beaks, more ventricose be- 
low, extremely compressed toward the extremity of the hinge and pos- 
terior margin. Beaks terminal, small and pointed ; hinge-line straight, 
