52 
PROCEEDINGS OF THE ACADEMY OP 
Unio nucalis. 
Shell oval, moderately gibbous ; extremities ratlier narrowly rounded, the 
most projecting part of the posterior end being below the middle, and that of 
the anterior extremity above it ; base semioval, often quite prominent in the 
middle ; beaks a little depressed, located about half way between the centre 
and the anterior end ; umbonial region rather gibbous, and rising above the 
hinge, subangular on the posterior slopes. Surface marked by fine lines of 
growth, and more or less distinct concentric wrinkles ; the latter becoming 
quite small and very regular on the beaks. Traces of extremely small regular 
radiating wrinkles are also sometimes seen between the obscure angle on the 
back part of the umbones, and the hinge. Length 1-85 inches ; height 1-34 
inches ; breadth 1 inch. 
"We were at first in much doubt about referring this shell to the genus Unio^ 
because it is associated with a small oyster and Ammonites Henryi of this paper. 
The hinge, however, as far as we have been able to make out its characters, is 
like that of the genus Unio, and entirely different from Cardinia, and other 
forms usually resembling Unio. In the left valve, (we have not seen the hinge 
of the right valve,) it is moderately thick, somewhat arched, and provided 
with two posterior lateral teeth, which are elongated parallel to the cardinal 
edge, and separated by a groove apparently for the reception of a tooth in the 
other valve. The cardinal tooth, which is placed nearly under the beak, is 
rather irregular, somewhat flattened, and a little corrugated on the edge. 
In addition to the foregoing characters, we are led to think this must be a 
true Unio, from finding in the same matrix several specimens of a small PIa~ 
norbis and a fragment of Paludina. 
Locality and position. — Southwest base of Black Hills, in lower part of No. 1. 
CORBULA INORNATA. 
Shell small, trigonal, very gibbous ; anterior side more or less rounded ; pos- 
terior extremity angular below, base semiovate, the most prominent part being 
towards the front ; hinge sloping from the beaks, which are central ; posterior 
umbonial slopes angular. Right valve more convex than the other, and hav- 
ing its beak more gibbous, elevated and incurved ; but the margins of the two 
valves are equal, nearly or quite closed, and a little warped. Surface nearly 
smooth or only marked by very obscure lines of growth, and sometimes a few 
indistinct concentric wrinkles near the base. Length '27 inch ; breadth '29 ; 
height of larger valve 23 inch, of smaller 20 inch. 
We have not yet had an opportunity to see the interior of this shell, but 
owing to the fact that there is often seen on the posterior side of each valve, 
just within the posterior umbonial angle, a rather distinct groove curving down 
from the beaks, directly over the position of the raised internal lamina in our 
genus Corhulamella, we suspect this species may possibly be found to possess; 
the internal characters of that genus. 
Locality and position. — Long Lake, No. 5, of the general section. 
Panop^a (Myacites) subelliptica. 
Shell narrow, subelliptical, or subovate, moderately compressed, extremities 
narrowly rounded, the posterior end being more compressed than the other, 
and sometimes very faintly truncate on the oblique upper slope, both ends 
apparently nearly closed, or but slightly gaping. Base forming a very broad 
gentle curve, rounding up gradually towards the extremities ; dorsal outline 
slightly concave in front and rear of the beaks, the anterior slope being more 
abrupt than the other. Umbonial region obscurely angular on the posterior 
side ; beaks rather depressed, but rising above the hinge, approximate, and 
located in advance of the middle. Surface of cast marked by small, moderately 
distinct, irregular concentric wrinkles of growth. Muscular and pallial im- 
[March, 
