44 GEOLOGICAL SURVEY OF THE TERRITORIES. 
It is not a very rare species, but no examples have ever been obtained 
which are in a better condition than those are from which Mr. Meek 
drew his description, and which are all in the form of natural casts, 
mostly of the interior of the shell. Therefore a figure only of one of 
his type specimens is given on plate 19. 
His original description is as follows : 
‘Shell attaining a medium size, or larger, rather thin; longitudinally 
ovate, being somewhat less than twice as long as high, with the widest 
(highest) point in advance of the middle; rather distinctly convex; an- 
terior side wider than the other, and regularly rounded; posterior mar- 
gin nore narrowly rounded, or sometimes obliquely subtruneate above; 
basal outline forming a broad, semi-ovate curve, with the most prominent 
part in advance of the middle; beaks moderately depressed and placed 
between one-third and one-fourth the length of the valves from the an- 
terior margin; surface smooth, or only showimg marks of growth; car- 
dinal teeth prominent, and bearing, in internal casts, a very profound 
impression, ranging vertically just behind the anterior muscular sear; 
lateral teeth long and straight, two in the left and one in the right valve. 
“Length, 3.80 inches; height, 2.20 inches; convexity, 1.40 inches. 
‘This will be readily distinguished from that I have provisionally re- 
ferred to, U. tellenoides Hall, by its proportionally longer and more 
convex valves, stouter hinge, and particularly by having larger, thicker, 
and more prominent cardinal teeth, ranging vertically instead of very 
obliquely forward and downward. 
“* Locality and position.—Chureh Buttes, Wyoming Territory; miocene 
[eocene] tertiary, in a rather coarse greenish grit.” 
Figure 1 a, on plate 19, is drawn from one of Mr. Meek’s types, which, 
although so imperfect, is one of the best examples yet discovered. 
Mr. Meek does not mention the group from which his specimens of 
this species were obtained, but as Church Buttes are composed of 
Bridger strata, they are doubtless from that group. The full charac- 
teristics of this species are not yet satisfactorily known, because its outer 
surface and complete external form have not been fully shown by any 
of the specimens yet discovered. It probably occurs at different hori- 
zons throughout the Green River Group also, but as the specimens of 
Unio found in all three of the Eocene fresh-water groups are so gener- 
ally in the form of casts, the identity of the forms referred to with this 
species has not been satisfactorily determined. Some examples, also, 
that have been discovered in the Wahsatch Group appear to belong to 
this species; but these, too, have been found only in the form of casts. 
GASTEROPODA. 
Genus PLANORBIS Miiller. 
PLANORBIS CIRRATUS White. 
Plate 19, figs. 5 a, b, and ¢. 
Planorbis cirratus White, 1879, An. Rep. U. 8S. Geol. Sur. Terr. for 1877, p. 251. 
Shell small, discoidal; volutions six or seven, very slender, their trans- 
verse diameter a little greater than their vertical, coiled closely and so 
nearly in a plane that the upper and under sides respectively are dis- 
tinguished mainly by the difference in the direction of the lines of growth 
upon the surface; the contact of the volutions is such as to produce a 
Slight concavity upon the inner side of each, all the outer and exposed 
