WHITE. } ot LARAMIE FOSSILS. 79 
15 millimeters; thickness, both valves together, 10 millimeters. There 
are two or three examples in the collection which were obtained from a 
layer separated by only a few feet from the one containing the typical 
specimens, at the Crow Creek locality, which seem to belong to this 
species, but, as they have some slight modifications of form besides their 
greater size, they are referred to it with doubt, and the size of the spe- 
cies is given as above. 
This shell plainly belongs to the subgenus Leptesthes of Meek, but it 
is the smallest species yet known, as the type species is the largest. 
The species here described shows characteristics of the subgenus that 
were not mentioned by Meek in his diagnoses. The inner surface of each 
valve is marked by asomewhat broad, faintly raised, smooth ridge which 
traverses the valve nearly perpendicularly from beneath the beak to the 
basal border. This ridge is always faint, and in the species here con- 
sidered it appears to be formed by a sudden thickening of the whole 
test forward of the median portion of the shell, rather than by a linear 
elevation of shell substance, such as constitutes the so-called internal 
rib of some shells. The beaks are also small, and the umbones not so 
prominent in the case of all species of this subgenus, as they are in the 
typical forms of the genus, and especially in the subgenus Veloritina. 
The peculiar flattening of the umbonal and upper and middle portions 
of the valves of C. (V.) macropistha, its greater width and equal if not 
greater thickness behind than in front, are characters by which the 
species may be readily recognized. 
Position and locality—Laramie Group; valleys of Crow and Bijou 
Creeks, Northern Colorado; associated with the last described and 
other species. 
CORBICULA (LEPTESTHES) SUBELLIPTICA Meek & Hayden. 
The type specimens of this species were collected by Dr. Hayden from 
the Judith River series of the Upper Missouri River region; and Mr. 
Meek also recognized it among some collections that were brought in by 
one of the parties of this survey from the valley of Bijou Creek, North- 
ern Colorado. I also collected it at the latter locality, where I found it 
associated with the preceding and other species. Mr. Meek described 
and figured it in vol. ix, U. 8S. Geol. Sur. Terr. (4to ser.), p. 523, plate 43. 
Subgenus VELORITINA * Meek. 
CORBICULA (VELORITINA) DURKEEI Meek. 
This species, which is the type of the subgenus Veloritina, has been 
found only in the Bear River series of the Laramie Group, where it is 
one of the most characteristic fossils. The typical examples were ob- 
tained in Bear River Valley, near the mouth of Sulphur Creek, but the 
Species is known to range as far south as Southwestern Utah, some ex- 
amples of it having been brought in by one of the parties under the 
direction of Lieutenant Wheeler; and figured and described by me in 
vol. iv, Expl. and Sur. West of the 100th Meridian. It is figured and 
described by Meek in vol. iv, U. 8. Geol. Sur. 40th Parallel (King), p. 
167, pl. xvi, figs. 6 and 6 a, d, ¢, d, e, f, and g. 
This species, the type of the subgenus Veloritina, seems to be suffi- 
*For a diagnosis of this subgenus see vol. ix, U. 8. Geol. Sur. Terr. (4to ser.), p. 
161. 
