Wuute. | LARAMIE FOSSILS. 69 
upper strata of the Laramie Group at Black Buttes Station, Wyoming, 
where also some imperfect examples of a species apparently identical 
with U. cryptorhynchus have been found. This species differs from U. 
proavitus, however, in wanting the umbonal and postero-dorsal ridges 
and oblique posterior truncation of the last-named species, and also in 
having the front margin projecting a little beyond the beaks, instead of 
having the beaks projecting a little beyond the front margin as they do 
in U. proavitus. 
Position and locality.—Prof. E. D. Cope discovered this species in 1876 
in strata of the Judith River series of the Laramie Group, on Dog Creek, 
a tributary of the Upper Missouri River. As already stated, it appar- 
ently exists also in the upper strata of the Laramie Group at Black 
Buttes Station, Union Pacific Railroad, Wyoming. None of the speci- 
mens found at the latter locality are, however, sufficiently perfect for 
satisfactory determination. 
UNIO SENECTUS White. 
Plate 28, figs. 1 a, b, and e. 
Unio senectus White, 1877, Bull. U. S. Geol. Sur. Terr., vol. iii, p. 600. 
Shell elongate-subelliptical in marginal outline; convexity of the 
valves comparatively slight, and nearly uniform over the whole surface; 
test thin; both basal and dorsal margins broadly convex, or the former 
sometimes a little straightened; front regularly rounded; posterior 
margin also rounded, but sometimes more abruptly so than the front ; 
beaks scarcely definable as such from the body of the shell, situated at 
about one-fifth the length of the shell from the front; hinge well de- 
veloped ; cardinal teeth prominent, but somewhat thin; lateral teeth 
long and weil formed, having between their anterior end and the cardi- 
nal teeth a considerable plain space. Above and behind a line drawn 
from the beaks to the postero-basal margin, that is, along the line of the 
umbonal ridge, when one is present, the surface is marked by very 
humerous small creuulated undulations, which increase in number both 
by implantation and. bifurcation with the increasing size of the shell; 
their general direction being backward, but along the dorsal portion 
of the valve they are flexed upward and end upon the dorsal margin. 
Below and in front of this line the surface is plain, being marked only 
by the ordinary lines of growth, except some fine radiating lines which 
appear in the substance of the shell when it has been exfoliated. 
Length, 80 millimeters; height, 40 millimeters. 
In its general form and surface characters, this species somewhat 
resembles the living Margaritana rugosa Barnes, but the undulations 
upon the postero-dorsal surface are much smaller, more numerous, and 
they occupy a proportionally broader space upon the surface of the shell 
than they do in that species; besides which the species here described 
is a true Unio, and not a Margaritana. 
Position and locality.—Strata of the Judith River series of the Laramie 
Group, valley of Dog Creek, a tributary of the Upper Missouri River, 
Montana, where it was discovered by Prof. E. D. Cope in 1876. Mr. J. 
A. Allen also brought in examples of this species from the valley of 
Yellowstone River, Montana. 
