GASTROPODA. 1049 
Trochonema vagrans.]} 
The test also is much thicker, the surface markings coarser, the angles more prominent, and the umbil- 
icus smaller. The last whorl often shows a tendency to become disjoined, but this feature is never so 
pronounced as in our 7. vagrans. Casts of the interior, because of the thick shell, have unusually rounded 
whorls, and these are even more readily distinguished from 7. umbilicatum than are the shells. The upper 
of the two peripheral carine is always clearly indicated by a rounded ridge with minor revolving undula- 
tions as shown in our fig. 3. The lower carina, however, seems always to be but obscurely reproduced on 
casts. The umbilical ridge, on the other hand, is more distinct on casts than on the shell itself. As may 
be seen in fig. 4, it becomes quite obsolete with age. In the Minnesota form of the species the whorls 
seem always to be more slender than in specimens from Wisconsin. 
Formation and locality—Stones River group, Minneapolis and St. Paul, Minnesota; Mineral Point 
and Beloit, Wisconsin, and Dixon, Illinois. 
Collection.—E. O. Ulrich. 
TROCHONEMA VAGRANS, 7. Sp. 
PLATE LXXVII, FIG. 46; PLATE LXXVIII, FIGS. 10—13. 
This form is closely related to J. beloitense—perhaps merely a variety of that species. It has more 
slender volutions, a thinner shell and, considering the size of the specimens, stronger surface markings. 
The shell being of only moderate thickness, the whorls of casts are also more angular. The last whorl is 
over half free and drops rapidly. 
Formation and locality.—Stones River group, Vanuxemia bed, Minneapolis, Minnesota. Apparently 
a rare fossil. 
Collections.—Geological and Natural History Survey of Minnesota; EH. O. Ulrich. 
' Museum Register, No. 6865. 
TROCHONEMA RUGOSUM, ”. sp. 
PLATE LXXVII, FIGS, 19—22. 
Shells of this species have a much smaller umbilical perforation than T. wmbilicatum. This is due 
chiefly to the much thicker shell, the size of the umbilicus in casts of the two species being more nearly 
equal. For the same reason the mouth of 7. rugosum, as seen on casts, appears to be abruptly expanded, 
especially upon the lower and outer sides. The upper side of the whorls (in casts) is also more strongly 
convex (not angular) in the inner half and more deeply concave in the outer. On both the cast and shell 
the two peripheral carine are more prominent, causing the space between to be more excavated. The 
surface markings are very coarse, turned backward on the upper side of the whorls, vertical on the concave 
peripheral face and again turned backward, though not as strongly as in 7. umbilicatum, on the lower side. 
Here, particularly toward the aperture of adult examples, the strie# are often more numerous, sometimes 
two to one, than on the peripheral band. 
Formation and locality —Stones River group, Vanuxemia bed, Minneapolis and St. Paul, Minnesota; 
Beloit, Wisconsin. 
Collections.—Geological and Natural History Survey of Minnesota; E. O. Ulrich. 
TROCHONEMA ECCENTRICUM, 2. sp. (Ulrich.) 
PLATE LXXVII, FIGS. 17 and 18. 
Young examples of this species must be almost indistinguishable from VT. umbilicatum, the general 
aspect and surface markings being practically the samein both. Fully grown examples, however, are 
separated at once by the basal or umbilical ridge which, instead of maintaining a submedian position, is 
swung outward gradually in the latter half of the last tura until it is immediately beneath the periphery, 
This peculiarity results in well-marked differences in the shape of the mouth, the latter appearing more 
