68 GEOLOGICAL SURVEY OF THE TERRITORIES. 
umbonal sinus and the posterior margin; but sometimes they radiate 
irregularly to the posterior and postero-basal margins. 
Length of an adult example, 45 millimeters ; height from base to 
beaks, “42 miilimeters. 
This species presents a greater degree of differentiation from what 
may be regarded as the typical form of Unio than any other known fos- 
sil species, and fully as great as that of any species now living, even in 
North America fluvatile waters. It is of the same type as the living 
species U. rugosus Barnes, and in many respects it resembles that shell. 
Like many other fossil Uniones of the western portion of North America, 
it has representatives among living types that are now peculiar to this 
continent. 
Position and locality—Upper portion of the Laramie Group, Black 
Buttes Station, Union Pacific Railroad, Wyoming, where it is associated 
with all the preceding species of Unio herein described, and also with 
other fresh-water species, including several Gasteropods. 
UNIO DANZ Meek & Hayden ? 
Plate 27, Figs. 2 a and b. 
Unio dane was originally discovered in strata of the Judith River 
series of the Upper Missouri River region by Dr. Hayden. It is figured 
and described by Meek in vol. ix, U. S. Geol. Sur. Terr. (4to ser.), p. 
518, plate 41, figs. 1 a@and b. From the upper strata of the Laramie 
Group at Black Buttes Station, and associated with all the species 
of Unio that are described on the foregoing pages, some well preserved 
examples have been obtained which seem to belong to the species in 
question. Two examples are figured on plate 27, showing, respectively, 
the exterior and interior surfaces. All these examples show that the 
surface, even in the case of fully adult shells, was more than usually 
smooth; in which respect, as well as in others, it resembled the living 
species U. rectus Lamarck. 
UNIO CRYPTORHYNCHUS White. 
Plate 24, figs. la and b. 
Unio crypterhynchus White, 1877, Bull. U. 8. Geol. Sur. Terr., vol. iii, p. 600. 
Shell of medium size, ventricose, subelliptical in marginal outline; 
height a little greater forward of the mid-length than elsewhere; test 
moderately thick; dorsal margin nearly straight or slightly convex; 
basal margin broadly convex; posterior margin regularly rounded; front 
margin also regularly rounded from beneath the beaks to the ventral 
margin; beaks rather large, distinctly defined from the body of the shell, 
not elevated, but projected forward and turned strongly inward, placed 
near the anterior end of the shell, but not reaching quite so far forward 
as the anterior border, between which and the beak there isa distinct 
sulcation; cardinal teeth strong; each valve having behind the cardinal 
teeth a moderately deep crypt or cavity of the beak; lateral teeth well 
developed, but thin and sharp. Surface marked only by the ordinary 
lines and lamellations of growth. 
Length, 70 millimeters; greatest height from base to umbo, 45 milli- 
meters. 
This species bears some resemblance to U. proavitus White, which has 
been described on a foregoing page. That species was found in the 
