WHITE. ] LARAMIE FOSSILS. 83 
This species differs from R. priscus Meek, with which it is associated, 
in the less robust and more elongate form of the shell, its proportionally 
longer spire, more delicate and finer surface markings, and the less ab- 
rupt convexity of the volutions upon the proximal side of the suture. 
Position and locality.—This form has yet been found only in strata of 
the Bear River Laramie series, near the mouth of Sulphur Creek, Bear 
River Valley, Wyoming, where it is associated with R. priscus, and 
numerous other molluscan forms characteristic of that series. 
Genus ACROLOXUS Beck. 
ACROLOXUS MINUTUS Meek & Hayden. 
This is the only species belonging to the Ancylide that has yet 
been discovered in any strata of the Laramie Group. It was obtained 
by Dr. Hayden from the Laramie strata, near Fort Union, in the Upper 
Missouri River region, and is described and figured in vol. ix, U. 8. Geol. 
Sur. Terr. (4to ser.), p. 543 plate 44, fig. 10. 
Genus PLANORBIS Miller. 
PLANORBIS CONVOLUTUS Meek & Hayden. 
The Planorbis section of the Limneide is not well represented among 
the pulmonate molluscea of the Laramie Group. Besides the three forms 
here noticed, all of which are from Laramie strata of the Upper Missouri 
River region, only one other form is yet known in the whole Laramie 
Group, although other fresh-water species of both pulmonate and branch- 
iferous mollusks are common, and species of Planorbis are also common 
in the fresh-water formations that succeeded the Laramie Group. The 
excepted species referred to is a small undescribed form from the Bear 
River Laramie strata near the mouth of Sulphur Creek, in Bear River 
Valley, which is properly referable to the subgenus Gyraulus Agassiz. 
It should be remarked, however, that another form, Planorbis (Bathy- 
omphalus) kanabensis White, has been discovered by Professor Powell 
in strata which he is understood to regard as equivalent to the Laramie 
Group, at Upper Kanab, Southern Utah; which species is noticed in the 
introductory remarks of this article. It is an interesting fact that the 
subgenus Bathyomphalus as well as Gyraulus was introduced thus early. 
Indeed it is probable that these two subgenera were introduced as early 
if not earlier than the form which is usually regarded as the typical of 
the genus. 
P. convolutus is described and figured in vol. ix, U. 8. Geol. Sur. Terr. 
(4to ser.), p. 536, plate 42, figs. 12 a and D. 
Subgenus BATHYOMPHALUS Agassiz. 
PLANORBIS (BATHYOMPHALUS) AMPLEXUS Meek & Hayden. 
See vol. ix, U.S. Geol. Sur. Terr. (4to ser.), p. 539, plate 42, figs. 16 
a, b, c, d, and e. 
PLANORBIS (BATILYOMPHALUS) PLANOCONVEXUS Meek & Hayden. 
See vol. ix, U. S. Geol. Sur. Terr. (4to ser.), p. 538, plate 44, figs. 9 
a, b, and ¢. 
