WHITE.] LARAMIE FOSSILS. 89 
Position and locality.—Laramie strata, near the top of the group; Black 
Buttes Station, Union Pacific Railroad, Wyoming; and valley of Yampa 
River, near Canon Park, Northwestern Colorado, where also its position 
is near the top of the group. 
NERITINA NATICIFORMIS White. 
Plate 30, figs. 3 a and b. 
Neritina naticiformis White, 1878, Bull. U. S. Geol. Sur. Terr., vol. iv, p. 715. 
Shell very small, subglobose, its aspect being more nearly like that of 
Natica than that of the usual forms of Neritina ; spire moderately prom- 
inent; volutions three or four, increasing so rapidly in size that the 
last one comprises much the greater part of the bulk of the shell; all 
the volutions regularly convex; suture distinct; test not massive; aper- 
ture large, nearly straight on the inner side, the remainder of its border 
forising a continuous and almost uniform curve, the whole comprising 
more than a semi-circle; edge of the outer lip thin; inner lip not very 
broad, flattened, apparently smooth both upon its surface and inner 
edge, sloping strongly inward, or away from the border of the aperture, 
its Inner margin somewhat concave. Surface marked only by ordinary 
distinct lines of growth, except that in one or two instances traces of 
revolving striz have been detected upon the proximal or lower portion. 
Extreme length from apex to front margin, 6 millimeters; greatest 
diameter across the middle of the aperture, about the same. 
In general aspect this little shell so closely resembles a Natica that, 
the aperture being filled with the imbedding material, the first sugges- 
tion whether it might not belong to that or a closely-related genus came 
from its association with fresh and brackish water forms. Upon break- 
ing up some of the examples the inner lip was found to be more charac- 
teristic of Neritina than Natica, although it is not so broad and thick as 
it usually is in typical forms of the former genus; from which the shell 
in question also departs by the comparative thinness of the test. 
The genus Neritina is not very well represented in the Laramie Group, 
no example of any species of it having yet been discovered in the Upper 
Missouri River region which has furnished so many other specific forms, 
and only three species have been found in the group elsewhere, includ- 
ing the next described form under the subgenus Velatella. It was more 
common in the preceding Fox Hills epoch, but it appears to have been 
entirely absent from the fresh waters in which the Tertiary deposits were 
made, that immediately succeeded those of the Laramie Group. 
Position and locality—Bear River, Laramie series, pear the mouth of 
Sulphur Creek, Valley of Bear River, Wyoming, where it was found as- 
sociated with Limnea vetusta, Acella haldemani, and other forms, in a 
layer both above and beneath which are those that contain an abun- 
dance of the characteristic brackish and fresh water species of that series. 
Subgenus VELATELLA* Meek. 
VELATELLA BAPTISTA White. 
Plate 29, figs. 6 a and b. 
Velatella baptista White, 1878, Bull. U. S. Geol. Sur. Terr., vol. iv, p. 715. 
Shell small, elliptical in lateral outline, broadly convex above, the con- 
vexity of the postero-median portion being greater than it is elsewhere, 
