WHITE. ] LARAMIE FOSSILS. 101 
either of the others, and the tubercles of this row are, when of full size, 
elongated, not in the direction of the row, but their axes are a little 
oblique to it. The proximal row (not the one which sometimes appears 
on the flattened proximal side of the last volution, but which is usually 
absent) is directly upon the angulation which is formed by the meeting 
of the flattened proximal and the outer sides of the volutions. 'There 
is sometimes another row of tubercles between these two, but it is often 
absent or reduced to only an obscure raised line. Sometimes the tuber- 
cles are so strong as to give the shell a conspicuously rugged appearance, 
but other examples are so slightly marked in this respect as to appear 
much like specimens of true Viviparus. Such examples very closely 
resemble V. trochiformis Meek & Hayden, as may be seen by comparing 
figures of that form with figure 2 g on plate 28. Indeed, notwithstand- 
ing the accepted generic differences between them, the two forms are 
probably genetically related. If so, one of the forms has gained a gen- 
eric characteristic without losing all its specific ones. It should be re- 
marked, however, that the operculum of this species has not yet been 
discovered. ‘This organ is quite characteristic in living forms of Tulo- 
toma, and without a knowledge of it in the case of the fossil form we 
cannot be positively certain that it is generically separable from Vivi- 
parus. 
Length of a large example, 38 millimeters; diameter of the last volu- 
tion, 25 millimeters. 
This species resembles the recent species T. magnifica Conrad, but it 
differs from that form in its less convex volutions, its faintly-impressed 
suture, and the different arrangement of its tubercles. It is the only 
known species of Yulotoma in American strata, but among European 
forms it may be compared with 7. ( Viviparus) strossmayerana Pilar. 
Judging from Brusina’s figures of that species, however, it differs in 
the less convexity of its volutions, especially that of the proximal side, 
and in the different character and position of the tubercles that mark its. 
surface. 
The specific name is given in honor of Prof. A. H. Thompson, formerly 
geographer of the United States Survey of the Rocky Mountain Region. 
Position and locality—Laramie strata, near the top of the group, at 
Black Buttes Station, Union Pacific Railroad, Wyoming, and also in the 
valley of Crow Creek, east of the Rocky Mountains in Colorado. 
Genus CAMPELOMA Rafinesque. 
CAMPELOMA VETULA Meek & Hayden. 
CAMPELOMA MULTISTRIATA M. & H. 
CAMPELOMA MULTILINEATA M. & H. 
Dr. Hayden obtained the types of these three species from the Laramie 
strata of the Upper Missouri River region. They are described and fig- 
ured in vol. ix, U.S. Geol. Sur. Terr. (4to ser.). The first two forms have 
also been discovered in the Bitter Creek series west of the Rocky Mount- 
ains, and the third one in the Laramie strata, east of those mountains 
in Colorado. The latter examples are represented by figs.4 a and b, plate 
28. The examples show a more distinct shouldering of the distal border 
of the last volution than is shown by Meek’s figured type; and some ex- 
amples brought by Mr. J. A. Allen from the valley of the Yellowstone 
ae still more robust and show a still more distinct shouldering of that 
order. 
