42 GEOLOGICAL SURVEY OF THE TERRITORIES. 
sal portion sometimes showing an oblique truncation or a sloping down- 
ward and backward of its border to a somewhat prominent posterior or 
postero-basal extremity ; beaks well defined but not prominent, situated 
about one-quarter of the full length of the shell from the front, or some- 
times less; umbonal slopes broadly convex. Surface marked by the 
ordinary concentric lines and imbrications of growth. 
Length of one of the largest examples in the collection, the one which 
is represented by fig. 2 a, plate 19, 65 millimeters; height of the same 
from base to dorsal margin, 43 millimeters; convexity of the single 
valve, 14 millimeters. Other examples have a greater, proportional 
length, as shown by fig. 2 b of the same plate. 
This species bears a closer resemblance to U. haydeni Meek, which 
has been reported from both the Green River and Bridger Groups, than 
to any other fossil form that has yet been published. 
It differs from that species in its larger size, its convex instead of 
Straight dorsal margin, its rather more prominent umbones, its some- 
what stronger hinge, and in its greater proportionate height from base 
to hinge margin. It belongs to that general group of the Uniones which 
have an oval marginal outline, the beaks submedially situated, and the 
surface plain; which group has several known representatives among 
the fossil Uniones of the western fresh-water tertiary deposits, and also 
a large number among living forms. In the latter respect it may be 
compared with U. fascinans and U. copei Lea, from the rivers of Virginia. 
It is not improbable that this species is really identical with U. telli- 
noides (= Mya tellinoides Hall, Frémont’s Expl. Oreg. and N. Cal., 1845). 
I have not had an opportunity, however, to examine Professor Halls 
type specimens, and, in view of the fact that several closely related 
species exist in the fresh-water deposits of the region from which Pro- 
fessor Hall’s types came, it is impracticable to determine from his figures 
and description alone to which species they were intended to apply. 
Fig. 2 a, plate 19, represents a typical example of U. shoshonensis from 
the Upper Green River Group of Southern Wyoming, and fig. 2 b, of the 
same plate, another more elongate example from the base of the Green 
River Group, or the top of the Wahsatch, in the valley of White River, 
Northwestern Colorado. 
Position and locality.—This species has a wide geographical distribution 
and a considerable vertical range. Its present known range is from the 
base of the Lower to the top of the Upper Green River Group, and it 
probably extends into the Wahsatch Group below and into the Bridger 
above. I have collected examples of it from the Green River Group in 
the valleys of Snake and White Rivers and Vermilion Creek, and from 
the slopes of Dry Mountains in Northwestern Colorado; also from the 
- Same group in the valley of Henry’s Fork, southward from Green River 
City, and near Alkali Stage Station, some twenty miles north of that 
place, in Southern Wyoming. 
UNIO WASHAKIENSIS Meek. 
Plate 19, figs. 3 a and b. 
Uirio washakiensis Meek, 1871, An. Rep. U. S. Geol. Sur. Terr. for 1870, p. 314. 
The following is Mr. Meek’s original description of this species (loc. cit. ): 
“Shell scarcely attaining a medium size, thin, depressed, rather com- 
pressed, longitudinally subovate ; anterior side short, rounded ; poste- 
rior side long, with a narrowly rounded or sometimes faintly subtrun- 
cated extremity, the most prominent point being below the middle, while 
above this there is usually an oblique slope from the posterior extremity 
