916 TEE PALEONTOLOGY OF MINNESOTA. 



(Bellerophon cluusus. 



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 striae 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 

 lip 7 mm. 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 th'en 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 lunulae. 



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. buryinensis 

 occurs with the typical form near liurgin and Danville, Kentucky. The species is limited to a vertical 

 range ot a few feet in the upper half of the group. 



Collections. Prof. J. M. Safford; E. O. Ulrich. 



BKI.LEROPHON CLAUSUS, n. 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, 



