916 THE PALEONTOLOGY OF MINNESOTA. 
[Bellerophon clausus. 
in some cases partly overhanging the umbilicus. Surface marked by growth lines 
only. They are more or less distinct, though on the whole fine. They are also some- 
what irregular, being generally arranged in bundles, which, especially near the aper- 
ture of adult shells, may produce obscure undulations of the surface. The course 
of the strize from the umbilicus to the dorsal carina is very little curved and nearly 
at right angles with the carina. However, just before joining the latter, they bend 
sharply backward. Hight of one of the largest of the Kentucky specimens 16 mm.; 
greatest width of the aperture 19 mm.; width of whorl just in front of edge of inner 
lip7mm. In Tennessee the species often attains a hight of 20 mm. 
We have before us an excellent series of silicified shells of this species and can 
testify to the unusual constancy of its specific characters. Considering this persist- 
ence we might be justified in separating the following form as a distinct species, but 
after considerable reflection we have concluded that such a course would not now 
be warranted. We propose then that it be known as 
Variety BurGINENSIS, n. var. (Ulrich.) 
PLATE LXIV, FIG. 6. 
This variety grew to be a litttle larger than the typical form (22 mm. in hight), 
has a proportionally less expanded mouth (the greatest diameter of the shell is 
about the same as the width of the aperture), more slowly enlarging volutions, and 
a larger umbilicus. On the best specimen the dorsal carina besides has the 
characters of a true slit-band and near the aperture it exhibits distinct lunule. 
B. troosti is one of a number of closely related Lower Silurian species. The 
group is well represented in the Trenton of Minnesota, but that B. troosti itself 
occurs here is as yet very doubtful. B. similis is very much like it, and before we 
found specimens showing the mouth and lines of growth, we unhesitatingly referred 
the casts of the interior to this species. Still, it is possible that B. troosti is really 
represented among the casts now assigned to B. similis. 
Formation and locality.—The typical form is not uncommon in the Trenton group at Nashville and 
Hartsville, Tennessee, and Danville, Frankfort and other localities in central Kentucky. Var. burginensis 
occurs with the typical form near Burgin and Danville, Kentucky. The species is limited to a vertical 
range of a few feet in the upper half of the group. 
Collections.—Prof. J. M. Safford; 4H. O. Ulrich. 
BrLLEROPHON cLAusuS, ”. sp. (Ulrich.) 
PLATE LXIV, FIGS. 7—10. 
In the general form of the shell and the course of the lines of growth, this 
species resembles B. troosti very closely. Carefully compared we find that the new 
species differs in several important respects, First the umbilicus is entirely closed, 
