wHITs.] TERTIARY FOSSILS. 43 
of the hinge; basal margin forming a broad semi-elliptic or semi-ovate 
curve, in the latter case the most prominent part being a little in advance 
of the middle; dorsal or hinge margin straight from the beaks to the 
upper slope of the posterior margin; beaks depressed nearly to the dor- 
sal margin, rather regularly convex, but not ventricose, and placed 
about one-fourth the length of the valves from the anterior extremity ; 
umbonal slopes moderately and evenly convex. Surface smooth or only 
showing more or less distinct marks of growth, excepting near the im- 
mediate points of the beaks, where well-preserved specimens show traces 
of minute regular longitudinal wrinkles which terminate posteriorly at 
two faint, oblique, obsolescent linear ridges; hinge slender; cardinal 
teeth small, oblique, and apparently consisting of one in the right and 
two in the left valve; lateral teeth straight, rather long, two in the left 
and one or two in the right valve. 
“Length of a large specimen 2.37 inches; height, 1.26 inches; con- 
vexity, 0.72 inch. 
“This species is related to U. priscus M. and H., with which it agrees 
nearly in form and surface characters. It is constantly smaller, how- 
ever, and distinctly thinner, while its hinge is weaker and its cardinal 
teeth smaller and much more oblique. The wrinkles on its beaks, and 
the two oblique linear ridges on their posterior dorsal sides, are similar 
to those on U. priscus, excepting that they are less distinctly defined and 
occupy a much smaller space only near the points instead of the whole 
surface of the umbones, being, in fact, so obscure and so near the points 
of the beaks as to be readily overlooked, and entirely obsolete in most 
es. 
“ It will be distinguished from U. haydeni mainly by its more depressed 
and more elongate form ; its stratigraphical position is also, according 
to Dr. Hayden’s observations, one thousand to two thousand feet lower 
in the series than that of U. haydeni.” ‘ 
Mr. Meek does not expressly state from which of the three great fresh- 
water groups of strata his type specimens came, but, judging from what 
is known of the strata at the localities he mentions (Washakie and 
Henry’s Fork, Wyoming), they are all from the Green River Group. 
The vertical range of the species, however, is apparently from the base 
of the Green River Group to at least the lower part of the Bridger 
Group. The type specimens from which Mr. Meek drew his description 
seem to have been lost or mislaid, and I have, therefore, not been able 
to examine them. The one from which fig. 3 a, plate 19, is drawn was 
found among other fossils that had been studied by him, and was la- 
beled in his handwriting, “From Church Buttes, Wyoming.” Church 
Buttes being composed of the strata of the Bridger Group, as well as 
the character of the stone embedding the shells, indicates that they 
came from that group, probably near its base. The specimen repre- 
sented by fig. 2b, of the same plate, is from the base of the Green River 
Group, in White River Valley, Northwestern Colorado. The species is 
well characterized by Mr. Meek, and the specimens here figured, as well 
as the others associated with them, answer well to his description. 
UNIO MEEKIL White. 
Plate 19, fig. 1 a. 
Unio leanus Meek, 1871, An. Rep. U.S. Geol. Sur. Terr. for 1870, p. 318. 
Unio meckii White, 1877, Bull. U.S. Geol. Sur. Terr., vol. iii, p. 665. 
The original name of this species was changed by the writer, as above 
indicated, because it had been preoccupied by Gray many years ago. 
