GASTROPODA. } 1051 
Trochonema subcrassum.] 
TROCHONEMA SUBCRASSUM, ”. Sp. 
PLATE LXXVII, FIGS. 30-34. 
The exterior of this form is in nearly all respects very similar to the internal casts of 7. fragile, and 
the specimens were at first regarded as testiferous examples of that species. However, on removing the 
shell, it became evident that it is much thicker, especially at the angles, than it can possibly be in 7’. 
Fragile, and that the internal cast is much less angular than are the casts of that species. Indeed, as is 
shown in fig. 33, the sharp external carine are only obscurely indicated on the interior cast. An equally 
important difference, and one that removes the species rather widely from all of the preceding species 
save 7’. bellulum, is the fact that the lines of growth, instead of continuing their general backward direc- 
tion on the peripheral face. are here turned forward to form a wide-angled notch as in many species of 
Lophospira. The lines of growth are very fine on the whole with many that are readily discernible to the 
unassisted eye. On the base they are not as strongly turned backward as in Z. fragile and most other 
species of the genus, so that the aperture is not as oblique as usual (compare plate LXXVII, figs. 15 and 
30). The upper carina is very near the suture and sometimes scarcely removed from it. 
The comparatively slight obliquity of the aperture in this and the next species (7. retrorsum) allies 
them with the forms included in the subgenus Hunema. 
Formation and. locality.—The types of this species are from the upper part of the Trenton group in 
Mercer and Boyle counties, Kentucky. A single cast of the interior, apparently Lelonging here, was found 
in the Fusispira bed near Cannon Falls, Minnesota. 
Collection —E. O. Ulrich (12 specimens). 
'TROCHONEMA RETRORSUM, 2. sp. 
PLATE LXXVII, FIGS. 35—38. 
In most respects like 7. subcrassum, but the mouth is even less oblique, the umbilicus narrower and 
much more abrupt, the shell thinner, the inner lip straighter, and the lines of growth even finer and more 
regular. The almost vertical wall of the umbilicus and the very slight backward curve of the lines of 
growth on the base of the shell are two very striking features when the species is compared with 7. 
umbilicatum and other species of that type. The mouth is pentagonal, the upper carina very near the 
suture. 
Formation and locality.—Ctenodonda bed, Black River group, Goodhue county, Minnesota, 
Collection.—E. O. Ulrich. 
TROCHONEMA MADISONENSE, n. sp. (Ulrich.) 
PLATE LXXVII, FIGS. 23—25. 
A large shell agreeing in most particulars with 7. wmbilicatum, but having relatively higher and 
more ventricose whorls, while the ridge, which generally surrounds the umbilical depression in this genus, 
is quite obsolete. The shell is thicker, the surface markings stronger, the mouth very oblique and with 
thicker lips. Casts of the interior of the two species are more alike than their exteriors, yet those of the 
present may be distinguished by the greater separation of the whorls due to the removal of a greater 
thickness of shell. There is a wide notch in the outer and upper portions of the peritreme which, with 
the somewhat triangular form of the aperture in a ventral view, suggests relations with 7. eccentricum. 
Figures of that shell are given on the same plate with those of this species, so it is scarcely necessary to 
compare them further. 
Formation and locality —Richmond group, Madison, Indiana. 
Collection.—H. O. Ulrich. 
