1050 THE PALEONTOLOGY OF MINNESOTA. 
[Trochonema bellulum. 
triangular than quadrangular ina ventral view though decidedly quadrangular ina basal view. The 
inner and lower lips also are more strongly reflected and thicker than in any other species of the genus 
known. And yet, the shell is not much thicker than in 7. umbilicatum. 
Formation and locality.—Upper division (‘‘Glade limestone”) of the Stones River group, near Leba- 
non, Tennessee. 
Collections.—Prof. J. M. Safford; E. O. Ulrich. 
TROCHONEMA BELLULUM, n. sp. (Ulrich.) 
PLATE LXXVII, FIGS. 26—29. 
At first we were inclined to unite this species with 7. eccentricum, but a more careful comparison 
revealed differences of sufficient importance to deserve recognition. In the first place the adult shell is 
much smaller, the width of the largest specimens being less than 25 mm. (in five out of six it is less than 
20 mm.), while it is from 35 to 40 mm. in adult shells of 7. eccentricwm. Next, the apical angle is usually a 
trifle narrower, giving a proportionally higher spire. Finally, the lines of growth are finer and turn 
slightly forward instead of backward in crossing the concave peripheral space, thereby producing, with 
the retrally curved striz# of the upper side, a slight notch at the upper peripheral carina. Such a wide- 
angled notch occurs in three other species, viz.: J. retrorsum, T. subcrassum and 7. madisonense of this 
report, but they are all readily distinguished from the present species by other characters. Compared 
with 7. umbilicatum, T. fragile and other similar species, 7. bellulum is distinguished at once by the 
eccentric sweep of the umbilical ridge and the subtriangular shape of the aperture resulting from it. 
Formation and locality.—Lower division of the Stones River group, Murfreesboro, Tennessee. 
Collections.—Prof. J. M. Safford; KE. O. Ulrich. 
TROCHONEMA FRAGILE, ”. sp. 
PLATE LXXVII, FIGS. 13—16, 
This isasmall form, the greatest diameter averaging about 15 mm., the largest seen being only 
about 22 mm. wide. The specimens closely resemble young testiferous examples of 7. umbilicatum, but it 
is to be noted that it is the internal cast that agrees in its general appearance with the exterior of that 
shell. We have not seen the exterior of 7. fragile, but the unusual sharpness of the angles indicates a 
very thin fragile shell, probably similar, even to the surface markings, remains of very delicate equal 
lines of growth being retained by one of the specimens, to the variety of T. umbilicatwm which we 
distinguish as var. canadense. The lower or umbilical side must be almost exactly as in that variety, but, 
judging from the differences exhibited between the interior and exterior of other species of the genus, the 
lower boundary of the vertical peripheral face must be even more prominent than in var. canadense. 
Further comparison brings to light another difference that we believe will serve to separate the species at 
all times from that variety. Namely, the uppermost of the four carine is proportionally much nearer the 
suture in 7. fragile, being removed from it but little more than one-fifth of the width of the upper surface 
of the whorl, whereas in all the varieties of 7. umbilicatum the distance equals at least a third. In this 
feature the speci’s agrees with 7. subcrassum and T. retrorsum, which see for comparisons. It is scarcely 
possible that 7. fragile can be confounded with any of the other species here described. 
Formation and locality.—Clitambonites and Fusispira beds of the Trenton group at various localities 
in Goodhue county, Minnesota. Also in beds equivalent to the latter horizon in Carroll county, Illinois. 
Collections.—Geological and Natural History Survey of Minnesota (2 specimens); W. H. Scofield (3 
specimens); H. O. Ulrich (7 specimens). 
Museum Register, No. 8735. 
