100 GEOLOGICAL SURVEY OF TIE TERRITORIES. 
VIVIPARUS LEAI Meek & Hayden. 
VIVIPARUS RETUSUS M. & H. 
VIVIPARUS PECULIARIS M. & H. 
VIVIPARUS TRUCHIFORMIS M. & H. 
VIVIPARUS REYNOLDSIANUS M. & H. 
VIVIPARUS LEIDYI M. & H. 
The types of the above-named six species were collected by Dr. Hay- 
den from the Fort Union series of the Laramie Group, in the Upper 
Missouri River region; they are described in vol. ix, U. S. Geol. Sur. 
Terr. (4to ser.), pages 577-582, and figured on plate 44 of the same vol- 
ume, except the third, of which there is a wood-cut accompanying the 
description. 
I think one cannot study these forms of Viviparus without becoming 
impressed with the belief that they are all genetically related. Indeed, it 
seems probable that further study of large collections of them will show 
that not more than two species ought to be made out of these six forms, 
even with the ordinary methods of discriminating study of fossil mol- 
lusca. From several localities in Utah examples of Viviparus have been 
brought in by different parties, some of which closely resemble the 
fourth, fifth, and sixth of the foregoing forms respectively. They are 
from strata that probably really belong to the Laramie Group, and are 
also probably related genetically with those forms. 
VIVIPARUS CONRADI Meek & Hayden. 
This form was obtained by Dr. Hayden from the Judith River series 
of the Laramie Group, where alone it has yet been discovered; but Mr. 
Meek thought it probable that V. peculiaris of the Fort Union series is 
only a variety of it. It is described and figured in vol. ix, U. 8. Geol. 
Sur. Terr. (4to ser.), p. 879, plate 42, figs. 15 a, b, c, and d. . 
Genus TULOTOMA Haldeman. 
TULOTOMA THOMPSONI White. 
Plate 28, figs. 2 a, b, ¢, d, e, f, g, and h. 
Tulotoma thompsoni White, 1876, Powell’s Rep. Geol. Uinta Mts., p. 134. 
Shell moderately large, having somewhat the general aspect of T. 
magnifica, the type of this genus; spire elevated, its sides having a broad 
general convexity, and the apex being somewhat blunt; volutions six 
or seven, their outer side flattened or slightly convex; proximal side of 
the last volution also flattened or slightly convex, producing a more or 
less prominent revolving angle between the proximal and outer sides of 
the last volution, but wiich is obscured in the spire by mutual contact 
of the yolutions. there; suture linear, or faintly impressed; umbilical 
perforation apparently wholly wanting in all cases. Surface of the three 
or four smaller volutions of the spire marked only by lines of growih 
and a few revolving lines, two of which are sometimes in the form of 
slight angulations; but the last two or three volutions are usualiy con- 
spicuously marked by prominent tubercles, which are arranged in two 
or three revolving rows, which extend to the aperture, and which are 
usually connected together in their respective rows by raised revolving 
lines. The distal row of tubercles on each volution is stronger than 
