186 Review of Geinilz on the rocks and fossils of Nebraska. 
Productus Cancrini de Vern. Geinitz, ib., iv, fig. 6. Whatever 
relations the shell here figured bears to German specimens iden- 
tified with P. Cancrinz, it certainly differs from the original Rus- 
sian type of that species, both in its proportions and in the 
prominence of its . At any rate I know it to range far 
down in the Coal-measure rocks of Kansas, below the horizon 
of the beds referred by Marcou and Prof. Geinitz to the Moun- 
tain limestone. 
Productus Orbignianus de Koninck. Geinitz, ib. figs. 8 to 11. 
Prof. Geinitz seems to be right in regarding this form as the 
same as P. splendens and P. Wabashensis N. & P. But Mr. Da- 
vidson, however, who ought to know, refers both of these, from 
specimens sent him from the typical localities, to the Carbonifer- 
ous species P. longispinus Sowerby. The shell figured by Prof. 
Geinitz is widely distributed and very abundant in our Coal 
measures, and in Kansas ranges up into the Permo-carboniferous. 
Productus horridus Sow. Geinitz, ib., fig. 7. There is no 
room whatever, to doubt but this is a young individual of the 
last mentioned species. That shell varies much in the distinct 
the umbo of mature specimens. If P. horridus was knows t 
occur in these rocks, it might be thought possible that this might 
be its young, but under existing circumstances, (that specie? 
being unknown in America), it would certainly require a cO® 
siderable stretch of imagination, to see in this little shell a: 
cies which at maturity attains nearly one hundred times its siZ® 
mucronata M. & W. Geinitz, ib., tab. iv, figs. 12, 14 
This is correctly identified; and his @. glabra (ib., figs. 15 to 18) 
seems to be a good species. Both of these species, howevel; 
range far below this horizon in Kansas and Sakiiaiehs even be- 
low the horizon of the beds referred by Professors Marcou and 
Shumard from the Coal-measures of 
: : veral specimens of it are in the Illinois ¢ 
lection from different localities in that state; and it is now know® 
, * Since this was written, I have had an opportunity to examine extensive collet 
tions ned by ebraska geological survey a hates of Dr. Hayden, at 
ng ' and : “re 
