88 GEOLOGICAL SURVEY OF THE TERRITORIES. 
examples of either of these two forms yet known. They are described 
by Meek in vol. ix, U.S. Geol. Sur. Terr. (4to ser.), pages 547 and 548, 
respectively. The former is illustrated on plate 42, figs. 6 a, b, ¢, and 
d; and the latter is illustrated only by wood-cuts accompanying the 
description. 
Genus HELIX Linnzus. 
HELIX VETUSTA Meek & Hayden. 
Dr. Hayden found this species associated with the preceding and many 
other species in the Judith River series. Itis deseribed by Meek in vol. 
ix, U.S. Geol. Sur. Terr. (4to ser.), p. 552, and figured on plate 42 of 
the same.volume. Although the Helicidz were introduced at least as 
early as the Laramie period, and different divisions of the family were 
then distinctly differentiated, the family is not abundantly represented 
in that group. 
Genus THAUMASTUS Albers. 
THAUMASTUS LIMN4IFORMIS Meek & Hayden. 
Discovered by Dr. Hayden in the Laramie strata near the mouth of 
Yellowstone River, Montana. It is described and figured in vol. ix, U. 
S. Geol. Sur. Terr. (4to ser.), p. 553, plate 44, figs. 8 a, b, c, and d. 
Genus COLUMNA Perry. 
COLUMNA TERES Meek & Hayden. 
COLUMNA VERMICULA Meek & Hayden. 
Both of these species were found associated together by Dr. Hayden 
in the Laramie strata, at the mouth of Judith River, Montana. They 
are described in vol. ix, U. S. Geol. Sur. Terr. (4to ser.), pages 555 and 
506, respectively, and figured on plate 44 of the same volume. 
Genus NERITINA Lamarck. 
NERITINA VOLVILINEATA White. 
Plate 21, figs. 6 a and b. 
Neritina volvilineata White, 1876, Powell’s Rep. Geol. Uinta Mts., p. 131. 
Shell small, subcireular in lateral outline; volutions three and a half 
or four; the last one regularly convex; spire short, but quite as promi- 
nent as is usual in species of this genus; suture slightly impressed; aper- 
ture semi-lunar; inner lip broad, plain, flat, its inner edge not clearly 
seen, but it is apparently plain. Surface marked by numerous raised 
revolving lines of unequal size, which increase in number by implanta- 
tion as the shell increases in size, the lines also gradually increasing in 
size for a portion of their length after their origination; the spaces be- 
tween the raised lines about equal to or a little less than the lines in 
width; the revolving lines crossed by the usual lines of growth, which 
gives the surface, upon some parts at least, an indistinctly cancellated 
appearance under the lens. 
Greatest diameter of the largest example among those first discovered 
at Black Buttes Station, 9 millimeters; height, the shell lying with its 
aperture upon the table, 5 millimeters. Some examples atterward dis- 
covered in the valley of Yampa River are much larger. 
