332 Review of Geinitz on the rocks and fossils of Nebraska. 
been found in Iowa by Dr. White, in limestone above the hor- 
izon of beds containing the same group of fossils characterizing 
Prof. Marcou’s division C at Nebraska City; while Pecten avicu- 
| latus, and Aviculopecten Coxanus, were found in that bed at the 
< last mentioned localit 
~e From all the foregoing facts, it will be seen, that 1 am com- 
. pelled to dissent from the conclusions adopted by Prof. Geinitz, 
: not only in regard to the dened of many of the Nebraska fos- 
: sils investigated by him to the European Permian species to 
which he has vllsieth them, but also respecting the age of the 
rocks from which they were obtained. Of the various species he 
identifies with foreign Permian forms, there are, it seems to 
not more than some four or five that are so closel y similar that 
no very satisfactory distinction can be detected, from exte! 
characters at least. These are it forms he refers to NM 
Beyrichi, Leda Kazanensis, Schizo sicus, Avicula spelun- 
s Lossi 
caria,* =(Pseudomonotis), and apace Pallast. The first four 
of these are, I'acknowledge, very similar to the Permian — 
to which he has referred them, while the fifth seems to be 
nearly like Plewrophorus costatus. The fact, however, that we 
now comparatively little of the hinge and interior of these shells, 
while they are mainly such forms as often present few reli 
external characters for specific distinction, and belong for the 
most part, to genera in which the species are os eed 
similar, ~~ weaken our confidence in these specific iden 
tions, under uch circu mstances. But when we take into coh 
tain limestone, and especially when we bear in mind, the DY 
merous os aE Carboniferous types with which they ar 
~ here directly associated in the beds under consideration, the - 
{ ae hae of basing important conclusions upon them must 
"he ome be urged, however, that with the aid of extensive ss 
aeons of Kuropean Permian species for comparison, 
- 
: | se 
_ be to a considerable extent true (for I have had for com compari 
_ a tolerable collection of the more common European on 
___ species), I_must still contend—with all due deference to bis rs 
ay pire — ord as a geologist—that his peculiar’ yee 
: was not found in Neb a a 
however > specituns from Nebraska doubtless the same He vn we 
— Mars tear sitter to the species Speluncaria 
