12 GEOLOGICAL SURVEY OF THE TERRITORIES. 
different aspect. Although two or three species of Unio from strata of 
the Laramie Group have the surface partially rugose, this form, with the 
exception of U. belliplicatus, is the only distinctly plicate one that has 
yet been found in any American strata. It differs from U. belliplicatus 
in its general shape and in the position and distribution of the plica- 
tions, which are most conspicuous on the anterior portion of that shell, 
while the corresponding portion of U. gonionotus is plain. 
Position and locality —Laramie strata, Upper Kanab, Southern Utah, 
where the only known examples of the species were collected by Pro- 
fessor Powell. 
Genus SPH/ZRIUM Scopoli. 
SPHZRIUM PLANUM Meek & Hayden. 
SPH4ZRIUM RECTICARDINALE M.& H. 
SPHZRIUM FORMOSUM M. & H. 
SPH4RIUM SUBELLIPTICUM M. &. H. 
These four species of Spheriwm were collected from the Laramie strata 
of the Upper Missouri River region by Dr. Hayden—the two former 
from the Judith River series, and the two latter from the Fort Union 
series. They are all described in vol. ix, U.S. Geol. Sur. Terr. (4to ser.), 
pages 526 and 527, and figured on plate 43 of the same volume. No 
other examples of Sphcriwm have been discovered in the Laramie 
Group, if we except a small undescribed form in the coal-bearing series 
near Evanston, Wyo. 
Genus CORBICULA Megerle. 
CORBICULA OBESA White. 
Plate 23, Figs. 3 a, b, ¢, d, and e. 
Corbicula obesa White, 1878, Bull. U. 8. Geol. Sur. Terr., vol. iv, p. 712. 
Shell small, or not above the average size common to this genus, 
inflated; sides somewhat regularly convex, suboval, or subtrihedral in 
marginal outline; transverse length somewhat greater than the height; 
basal margin almost regularly rounded, meeting both the posterior and 
anterior margins by regular and nearly equal curves; postero-dorsal - 
portion of the shell, as seen by side view, regularly rounded from the 
beaks to the posterior margin; antero-cardinal margin short and 
straight, but the shell has the appearance of being concave in front of 
the beaks on account of the slight elevation and forward prominence of 
the latter; postero-dorsal margin very little, if any, depressed below the 
adjacent portions of the shell; beaks small, pointed, not prominent, di- 
rected a little forward, and situated only a little in advance of the mid- 
length; lateral teeth well developed, slender, and apparently not crenu- ° 
late, but none of the examples in the collection are in a condition to 
show the natural surface of the teeth clearly; cardinal teeth well de- 
veloped, but not robust; pallial sinus small. Surface marked only by 
the usual lines of growth; and these being mostly very fine, the surface 
has a comparatively smooth, or sometimes even a polished, aspect in 
well preserved examples. 
Length of the largest example in the collection, 38 millimeters ; height 
of the same from base to umbo, 30 millimeters; thickness, both valves 
together, 25 millimeters. The average adult size is apparently consid- 
erably less. 
