WHITE.] LARAMIE FOSSILS. 61 
anterior and umbonal portions, and without distinct umbonal ridges ; 
beaks not prominent, situated about one-third the full length of the 
shell from the front; basal margin broadly semi- elliptical ; anterior 
margin regularly rounded from the cardinal Inargin ;to the base ; pos- 
tero-basal margin sloping upward to the posterior margin, which is 
sharply rounded to the cardinal margin; the latter margin slightly 
arched, or the anterior and posterior portions of it forming a very slight 
angie with each other; denticles minute, numerous, twelve to fifteen or 
more in front of the beak, and a somewhat greater number behind it. 
The very few examples of this species which have been discovered 
being in the form of natural casts in indurated shale, the true character 
of the surface is not accurately known, but it appears to have been 
marked only by ordinary concentric lines of growth. Character of the 
pallial and muscular impressions unknown. 
Length, 11 millimeters ; height from base to beaks, 5 millimeters. No 
examples larger than this were discovered, but it is probable that it is 
larger at full adult size. 
The occurrence of this genus within two hundred feet of the base of 
the group would not excite surprise, if it were not well known that the 
fresh and brackish water species which prevail in the Laramie Group 
are associated with it. The presence of the latter forms, however, in the 
same layers indicate that true marine conditions had ceased at the very 
beginning of the Laramie period. 
Position and locality —aramie Group ; associated with Corbula wndi- 
fera, Anomia micronema, Melania wyoningensis, &c.; Danforth Hills, 
near White River Indian Agency, Northwestern Colorado. 
Genus ANODONTA Cuvier. 
ANODONTA PROPATORIS White. 
Plate 24, figs. 2, a, b,e, and d. 
Anodonta propatoris White, 1877, Buli. U. S. Geol. Sur. Terr., vol. iii, p. 601. 
Shell elongate subelliptical in marginal astiie valves moderately 
and somewhat uniformly convex; beaks small, slightly elevated above 
the cardinal border; hinge-line lon gand straight ; basal border broadly 
convex ; front regularly rounded from the base up to the antero-dorsal 
border, which latter border is more abruptly rounded to the hinge-line ; 
postero-dorsai border oblique and slightly convex ; postero ventral border 
somewhat abruptly rounded from the postero-dorsal to the basal border ; 
cardinal margin slightly thickened but entirely plain and characteristic of 
the genus Anodonta. 
Surface plain, or marked only by the usual lines and undulations of 
growth. 
Length of the largest example in the collection, 62 millimeters: height 
of the same from base to beaks, 36 millimeters; length of a partly grown 
example, 37 millimeters; height of the same, 20 millimeters. 
This species is not only a true Anodonta, Dut in all its characteristics 
and its general aspect it very closely resembles several living American 
species of that genus. None of the examples are perfectly preserved, 
but the characteristics of the species are nevertheless well shown, and 
should perfect examples ever be discovered, it will probably be difficult 
to say how it differs from some one of the many closely similar living 
forms. It is not to be denied that in this case a separate specilic iden- 
