86 GEOLOGICAL SURVEY OF THE TERRITORIES. 
Genus BULINUS Adanson. 
BULINUS ATAVUS White. 
Plate 24, figs. 5 a and b. 
Bulinus atavus White, 1877, Bull. U. S. Geol. Sur. Terr., vol. iii, p. 601. 
Shell large, much elongated; volutions about seven, increasing gradu- 
ally in size; moderately convex; suture distinct but not deep; callus of 
the inner lip thin or absent; surface smooth, or marked only by very 
faint and very fine lines of growth. Some of the specimens have the 
appearance of having been naturally truncated or abruptly terminated 
at the apex, but it is more probable that this condition is the result of 
accident or erosion. 
Length, 50 millimeters, or more if the apex of the example measured 
be restored; diameter of body volution, 26 millimeters; length of aper- 
ture, 24 millimeters; full length of the spire beyond the aperture about 
equal to that of the aperture. 
This species is remarkable for its great size and unusually elongate 
form, which features render it so conspicuously different from any other 
known form as to make detailed comparison unnecessary. It is also 
so unusually elongate as to suggest that it may prove to be the type of 
a separate section of the genus Bulinus. 
Position and locality.—Judith River series of the Laramie Group; val- 
ley of Dog Creek, a tributary of the Upper Missouri River, where it was 
discovered by Prof. E. D. Cope. 
BULINUS DISJUNCTUS White. 
Plate 24, figs 6 a and bD. 
Bulinus disjunctus White, 1879, An. Rep. U. 8. Geol. Sur. Terr. for 1877,* p. 170. 
Shell rather large and moderately elongated; volutions about six, 
those of the spire increasing gradually in size, but the body volution is 
proportionally more inflated than those of the spire; suture distinct, 
but not deep, and not conspicuous, because of the moderate convexity 
of the volutions; length of the spire a little more than half that of the 
whole shell; callus of the inner lip broad, its posterior half closely 
appressed against and adherent to the body; its anterior half deflected 
or disjoined from the body, so as to leave a kind of umbilical space 
between it and the body of the shell. This condition of the inner lip is 
evidently not accidental, as it is present upon all the examples, young 
and old, that have yet been found; aperture moderately large, its length 
a little more than half the full length of the shell. Surface marked 
only by the fine lines of growth peculiar to the Physide. 
Length, about 43 millimeters; breadth of body volution, 20 millime- 
ters. 
This shell resembles B. subelongatus Meek & Hayden, from the Lara- 
mie strata of the Judith River series, Upper Missouri River region; 
*In the original description of this species I compared it with ‘“ Bb. elongatus Meek 
& Hayden.” B. subelongatus was intended, the error haying occurred by copying 
from one of the labels accompanying the type specimens. I have elsewhere inadvert- 
ently made a few similar errors in cases where the originally labeled name was 
changed upon publication. 
