WHITE. | LARAMIE FOSSILS. 99 
side; its outline a little straightened between the angle before mentioned 
and the verge of the umbilicus by contact with the body of the shell, 
but the remainder of the outline forming a continuous and almost regu- 
lar curve. Surface smooth, and having an almost polished appearance ; 
but it is marked by very fine lines of growth. 
Length from the front margin of the aperture to the apex, 18 milli- 
meters. 
This shell more nearly resembles the living species V. intertexta Say 
than any other known form; but it differs from that species in its some- 
what shorter spire, more distinct, though small, umbilicus, and the less 
prominently rounded distal side of the volutions. It also resembles V. 
leat M. & H., but it is a much shorter shell. 
Position and locality—Laramie Group, valley of Crow Creek, ten miles 
above the confluence of that creek with Platte River, Northern Colorado. 
VIVIPARUS COUESI White. 
Plate 30, fig. la. 
Viviparus couesi White, 1878, Bull. U. S. Geol. Sur. Terr., vol iv, p. 717. 
Shell very large when fully adult; volutions six or seven, convex, the 
distal side of the last one especially, abruptly rounded to the suture, 
giving it a somewhat shouldered aspect there, while the outer side is 
broadly convex and sloping gently forward and inward; suture deeply 
impressed, the apparent depth being increased by the great convexity 
of the volutions. Surface marked by the ordinary lines of growth, no 
revolving marks of any kind having been detected. The lines of growth 
indicate that the margin of the outer lip is nearly straight, as is usual 
with all species of this genus, and which feature distinguishes its shells 
from those of Campeloma, in which the outer lip is sinuous. Inner lip 
somewhat thickened by callus and reflexed at the proximal or anterior 
end, but not covering the umbilical fissure there, which is moderately 
large. ‘The precise shape of the aperture is unknown, but it is probably 
subovate. 
No entirely perfect examples have been discovered, but the largest 
one yet obtained would, if perfect, measure about 65 millimeters in 
length; full width of body volution, 38 millimeters. 
This species is deseribed by Meek, from an imperfect example, in U.S. 
Geol. Sur. 40th Parallel (King), vol. iv, p. 181, and figured on plate xvii, 
fig. 15, of the same volume; but it was not specifically named by him. 
He referred it to the genus Campeloma, but the numerous specimens that 
have been obtained from the same and other localities, as well as his own 
type specimen, show that the species possesses the true characters of 
Viviparus. It is distinguished from all other species of the genus known 
to me in American strata by its great size, and there are few other. 
forms with which it is in any danger of being confounded. From YV. 
puludineformis Hall it differs in its more robust form, inthe greater con- 
vexity of its volutions and the abrupt rounding of their distal side, and 
in the presence of a distinet umbilical fissure. 
Position and locality —Laramie Group, valley of Bear River, seven 
miles northward from Evanston, Wyo., and also near the mouth of 
Sulphur Creek, above Evanston. It is associated with other fresh-water 
forms, and also with many of the characteristic brackish-water species 
of that series. 
