60 
PROCEEDINGS OP THE ACADEMY OF 
angles, which, however, appear never to be rounded at the extremities. It is 
possible these smaller joints may belong to another species, though we incline 
to the opinion that they are only the joints of smaller individuals of the species 
here indicated. 
The star-like surfaces of the column joints above described, present some 
varieties of form, but usually resemble so closely those of S. scalaris, Goldf., 
that we are in some doubt about the propriety of considering our fossil a dis- 
tinct species. These joints are all much smaller than those figured by Goldfuss, 
and appear never to have had the angles so short and rounded as some of the 
examples given by that author and Quenstedt, of F. scalaris. 
Locality and position. — South and south-west base Black Hills ; Stone Butte, 
Lower part of bed C of the accompanying section. 
LiNGULA BREVIROSTRIS. 
Shell oblong elliptical, thin; lateral margins slightly convex, nearly parallel, 
sometimes converging a little towards the beaks in young individuals ; front 
subtruncate ; cardinal edge sloping to the beaks at an angle of about one hun- 
dred and thirty degrees; beaks obtuse, scarcely projecting beyond the cardinal 
margin ; valves nearly equal, convex along the middle, compressed near the 
margins and in front. Surface polished, and marked by fine rather obscure 
concentric striae ; on the surfaces of the inner laminae a few very obscure radi- 
ating, or longitudinal lines are sometimes seen along the middle of the valves, 
near the front. Length -54 inch ; breadth -35 inch ; thickness (depth of the 
two valves) -16 inch. 
Locality and position. — Western and south-western base Black Hills, towards 
lower part of bed C of foregoing section. 
Inoceramus umbonatus. 
We only know this species from an internal cast of a left valve, with 
portions of the shell adhering near the beak and hinge. This valve is 
remarkably gibbous, and the beak, which is a little oblique and near the 
anterior side, is much produced, elevated and involuted, so as to give the 
valve the appearance of some of the Palaeozoic univalves usually referred 
to the genus Capulus. The aperture of this valve is subcircular, being 
straighter on the hinge side than elsewhere. The portion of the shell remain- 
ing near the hinge is very thick, and composed of an inner laminated layer, 
and an external coarsely fibrous portion, the latter being much thicker than the 
other. We know nothing of the surface markings, beyond the fact that 
obscure concentric undulations are visible on the cast. 
The remarkable form of this valve indicates that the other must have been 
comparatively much less gibbous, or, perhaps, bore the relations to this, of 
an operculum to a univalve shell, as in 7. involutus of Sowerby. It is the first 
species of this type discovered in American formations, so far as we know. 
Height 3.10 inches ; length 2.38 inches. 
Locality and position. — This specimen was obtained from near Fort Benton 
on the upper Missouri ; but as it was found by a person unacquainted with 
geology, at a locality not yet visited by any person familiar with the formations 
of the country, its position is doubtful. The composition of the matrix, however, 
as well as the thickness and structure of the shell, lead us to think it 
holds a position in No. 4 of the general section ; all the north-western species 
yet known from formations below No. 3 being comparatively thin and entirely 
fibrous. 
Avicula (Monotis) tenuicostata. 
Shell suborbicular, or slightly oval, a little oblique, usually higher than long ; 
valves nearly equally convex; anterior side subtruncate, rounding rather 
abruptly into the hinge above, forming a broad oblique curve below ; basal and 
postero-basal margins rounded ; upper posterior margin sloping obliquely for- 
[March 
I 
