wuts. ] LARAMIE FOSSILS. 73 
The distinctly subglobose form and comparatively smooth surface of 
this species are distinguishing features, and it differs too greatly from 
any described form of the germs to ueed detailed comparison with any. 
While the greater part of the species found in strata of the Laramie 
Group that are referred to Corbicula vary in different characteristics 
and degrees from the typical forms of that genus, this one seems to 
possess the true typical characters. Atleast it is notreferable to either 
of the subgenera that have been proposed, and which are noticed on 
following pages. 
Position and locality—Laramie Group, valleys of Crow and Bijou 
Creeks, Northern Colorado, at which localities alone it has yet been 
found, and where it is associated with other species of Corbicula. 
CORBICULA CARDINIZFORMIS White. 
Plate 25, figs. 5 a and Db. 
Corbicula cardinieformis White, 1878, Bull. U. 8. Geol. Sur. Terr., vol. iv, p. 711. 
Shell somewhat above medium size for a species of this genus, trans- 
versely subelliptical, moderately gibbous, especially a little forward of 
and above the middle, but somewhat compressed towards the free mar- 
gins, especially in the posterior region; front and posterior margins both 
somewhat narrowly rounded, and the base broadly rounded, forming 
together nearly a semi-ellipse; cardinal margin broadly rounded, the 
postero-dorsal margin sloping gently downward from the beaks to the 
posterior margin; antero-dorsal margin slightly concave just in front of 
the beaks, where the slight inflexion of the valves also produces a slight 
concavity in the:shell when both valves are together; umbonal portion 
of each valve prominent; beaks narrowed, distinctly defined, not much 
elevated, but pointing strongly forward and incurved. Hinge and in- 
terior markings unknown. 
Length from front to rear, 59 millimeters; height from base to beaks, 
_ 38 millimeters; greatest thickness, both valves together, 28 millimeters. 
In external torm this species seems to occupy an intermediate position 
between the usual short or typical forms of Corbicula and that section 
of the genus which was separated from it by the late Mr. Meek under 
the subgeneric name of Leptesthes. In this respect it bears considerable 
resemblance to a form figured on plate 23, figs. 2a and b, which I re- 
gard as only a variety C. (Z.) fracta Meek. It differs, however, from that 
form, and from all other species of Leptesthes known to me in the promi- 
nence and distinct definition of the beaks; the umbonal region being 
broadly flattened and the beaks depressed and illy defined in all the 
published species of the subgenus Leptesthes ; which feature seems to 
be one of its distinguishing characteristics. It was found associated 
with C. cleburni, to which it bears some resemblance in general form, 
but it differs too greatly from it to need detailed comparison. 
Position and locality——Laramie Group, Valley of Crow Creek, 15 miles 
above the confluence of that creek with Platte River, Northern Colorado 
CORBICULA CLEBURNI White. 
Plate 23, figs. l a, b, and ec. 
Corbicula cleburni White, 1878, Bull. U. S. Geol. Sur. Terr., vol. iv, p. 711. 
Shell rather large, subcircular or subtrihedral in marginal outline ; 
height from base to umbo about equal to the extreme transverse length, 
