OF DENISON UNIVERSITY. 
85 
IX. var. parva, or young. 
(^Plate XIII, Pigs. 17 a, b.) 
Among the specimens of Orthis collected at the Soldiers’ Home 
Quarries occur great numbers of a small form resembling O. elegantula. 
The ventral valve is exceedingly convex and the surface is marked by 
fine, numerous, indistinctly preserved striae, being plainest at the lat- 
eral and anterior margins of the valve. The beak is very prominent 
and incurved. 
An ordinary sized specimen of the ventral valve measured gave a 
length of 6 mm.; breadth, 7 mm.; convexity, 3 mm. The largest 
specimen observed does not exceed 10 mm. in breadth. 
The variety occurs frequently in the limestone of the Clinton Group, 
whereas the species described above seems confined to the upper, shaly 
courses. The main reasons for separating it from the species are its 
smaller size, greater convexity, and different location. If not the 
young of O. elegantula it is certainly a well marked variety. Its gen- 
eral appearance is somewhat like that of O. pisa of New York strata, 
but our shell does not have both valves connected and the presence of 
an occasional dorsal valve having a low mesial depression, apparently 
to be associated with the ventral forms, would preclude such a deter- 
mination. For the present it may be considered a variety of O. ele- 
gantula. 
Locality and position. Widely distributed throughout the Soldiers’ 
Home Quarries, in all except the uppermost layers of the Clinton 
Group. 
X. Orthis fausta, sp. n. 
{^Plate XIII, Figs. 15 b,c, d) and Figs. 16 a, b.) 
Shell of medium size or often less, wider than long ; hinge line not 
equaling the width of the shell ; lateral margins rounded in front, pos- 
teriorly incurved, frequently expanding at the hinge line just enough to 
leave the postero-lateral margins extend a slight distance beyond the 
incurved portion of the same, like little ears. Convexity of the 
valves almost equal, that of the ventral valve being slightly the 
greater. 
Dorsal valve convex, with a distinct mesial sinus extending from 
the beak to a point about one third the distance from the anterior mar- 
gin, where it vanishes ; the greatest convexity lies a little behind the 
