870 THE PALEONTOLOGY OF MINNESOTA. 
(Protowarthia granistriata. 
limestones of Minnesota which may represent other varieties of the species, but as 
we cannot be certain about them we prefer to leave them unclassified for the 
present. 
Formation and locality.—Rather a common fossil of the Stones River group, at Mineral Point, Janes- 
ville and Beloit, Wisconsin, and Dixon, Illinois. In Minnesota it occurs, though not abundantly, in the 
Vanuxemia bed at Minneapolis, St. Paul and Cannon Falls. 
Collection.—E. O. Ulrich. 
PROTOWARTHIA GRANISTRIATA, 2. sp. (Ulrich.) 
PLATE LXIII, FIGS, 28—30. 
Shell scarcely reaching the medium size, closely coiled, leaving no umbilicus; 
center of dorsum raised into a low broad ridge, defined on each side by an obscure 
wide furrow; with age the outer boundaries of the latter increase gradually in 
distinctness, the back of the outer half of the last volution in the largest specimens 
presenting a flattened appearance; but the central ridge, though decreasing some- 
what in hight, continues to the aperture. In casts of the interior there is a small 
umbilicus, while the central ridge is nearly as on the shelf itself. Aperture trans- 
verse, about twice as wide as high, the width generally equalling the hight of the 
shell; sinus wide, only moderately deep, the margin of the lobes bending rather 
sharply where the apertural margin is intersected by the faintly raised boundaries 
of the flattened dorsum. Except in the umbilical regions the test is thin. Out of 
nearly thirty specimens, only two preserve anything of the external layer. These 
show that it is marked by fine lines of growth and by very delicate revolving lines. 
All of the other testiferous examples preserve only the inner and middle layers, the 
latter appearing in every case quite smooth. Most of the specimens preserve what 
may be called a fourth layer. This seems to have been deposited by the inner 
mantle over the inner volutions, including the smaller half of the outer, while on 
each side it extends around the callous filling of the umbilicus. The whole of this 
layer is finely granulose, except the lateral extensions and these are covered by 
wavy revolving striz. Hight of an average shell 19 mm.; width of aperture 19 mm.; 
median hight of same 9.8 mm.; width of inner volution 6 mm.; depth of sinus 5 mm.; 
width of same about 10 mm. 
In this species the sinus is only about half as deep as in P. rectangularis, the 
apertural lobes are not rectangular, the umbilicus is closed entirely, and the 
volutions rounded rather than subtriangular in cross section. It is nearer P. cancel- 
lata Hall, but that species has a slightly deeper sinus, and a rounder back, the back 
never being flattened, nor is there ever a sign of the low dorsal ridge and obscure 
furrows characterizing P. granistriata. 
