62 GEOLOGICAL SURVEY OF THE TERRITORIES. 
tity is assumed from its known antiquity, rather than proved by an as- 
semblage of specific characteristics. 
At the time of its discovery this was the only species of Anodonta that 
had ever been found in any strataof Western North America of either Mes- 
ozoic or Cenozoic age; and, with the exception of the next described 
species, it is the only known Anodonta yet known from any of the West- 
ern strata of the ages mentioned. 
Position and locality —tLaramie strata of the Judith River series, Dog 
Creek, and also upon the north side of the Missouri River, near Birch 
Creek, Montana, where it was collected by Prof. E. D. Cope in the sum- 
mer of 1876. ; 
ANODONTA PARALLELA White. 
Plate 24, fig. 3a. 
Anodonta parallela White, 1878, Bull. U. S. Geol. Sur. Terr., vol. iv, p. 709. 
Shell transversely much elongate, oblong or semi-elliptical in mar- 
ginal outline; valves gently convex, apparently a little more so near 
the front than elsewhere; beaks situated about two-sevenths of the 
whole length of the shell from the front, depressed, the elevation of the 
whole umbonal region being very slight or hardly perceptible ; hinge line 
long; the whole dorsal border nearly straight; both the anterior and pos- 
terior borders regularly rounded, that of the posterior end being a little 
more abruptly rounded than the front; base nearly straight, or perhaps 
very Slightly emarginate along or a little in front of the mid-length; test 
thin; surface smooth, or marked only by the usual lines of growth, and 
one or two faint linear ridges running from the beaks to the postero- 
dorsal margin. 
Length, 62 millimeters; breadth, 20 millimeters. 
The extraordinary length of this shell compared with its width is an 
unusual feature in Anodonta, but all its other characteristics, so far as 
they can be observed on the only examples that have yet been discov- 
ered, indicate it to be a true Anodonta, the correctness of which reference 
is also suggested by the fact that all its immediate associates are fresh- 
water forms. Only two examples have been discovered, both of which 
are imperfect, figure 3 a on plate 18 being a restoration drawn from both 
examples. 
Position and locality—Laramie Group, valley of Crow Creek, North- 
ern Colorado, about ten miles above the confluence of that creek with 
Platte River. 
Genus UNIO Retzius. 
UNIO ALDRICHI White. 
Plate 29, figs. 2 a and b. 
Unio aldrichi White, 1878, Bull. U. S. Geol. Sur. Terr., vol. iv, p. 710. 
Shell of medium size, transversely elongate, approximately oblong in 
marginal outline, height not diminishing posteriorily; valves moderately 
gibbous, especially along the umbonal slopes or ridges, and also forward 
of these; test moderately thick, becoming more so in old shells; beaks 
situated nearly one-third the full length of the shell from the front, in- 
curved, broad but not very prominent, although the flattened umbo is 
raised above the hinge line; umbonal ridge prominent, subangular ; 
