72 
BULLETIN OF THE LABORATORIES 
point half way to the point where the iimbonal ridge terminates. The 
single specimen seen is a little imperfect so the curvature of the beak 
could not be certainly seen. This shell is as large as A. siibciineala, 
which it greatly resembles in surface characters, but the presence of 
the Pleurophorus-like ridges and slightly angled posterior margin, and 
less convexity serve to readily distinguish it. 
Near the top of free-stone at Granville, collected by W. F. Cooper. 
This shell is apparently identical with S. nobilis, the only differ- 
ences noted being the slightly greater anterior projection in our speci- 
mens, which are thus rather longer. 
AUorisma cooperi% sp. n. 
(Plate VI, Figs. lo ) 
Shell of medium to large size, rather flat, expanded, and short. 
Very little more than twice as long as high ; middle region evenly 
■convex; beak not prominent, gently incurved, situated near the junc- 
ture of middle and anterior thirds. Hinge and lower margins nearly 
parallel, latter gently curved. Anterior margin rather long, slightly 
concave, meeting the lower m.argin below the middle at an acute pro- 
duced angle. Posterior margin parabolic, nearly equally curved above 
and below. The height is nearly the same at the anterior and poste- 
rior thirds.* The surface is marked with the usual concentric striae, 
but whether granulated or not the condition of our specimens forbids 
conjecture. The post-umbonal ridge is close to the hinge line and not 
very prominent, while the antero-dorsal margin has no lunule. 
Length 69 mm; height at beak 33 mm; distance of beak from 
anterior 20 mm. 
This is a much shorter species than A. subcuneata, M., of the 
coal-measures, and has a longer anterior portion. 
Two specimens from the upper layers of the free stone have been 
found with concurrent characters. Collected by W. F. Cooper, at 
Union Station, and by C. L. H., north of the “ Dug- way ” 
AUorisma zuincJielli, Meek. 
(Plate VIII, Figs. 2-4.) 
Occurs in great abundance in a layer immediately below the 18- 
