328 Review of Geinitz on the rocks and fossils of Nebraska. 
Geinitz, from this region, in part mentioned in my remarks pub- 
lished in the last number of the Journal. For convenience, in 
doing so, I will use the names by which he has designatéd them, 
as follows :— 
Cyathaxonia, taf. v, f.8. This form from Plattsmouth, compared 
by Prof. Geinitz, C. tortuosa Mich., is the same described by Me- 
Nebraska city, is probably only a variety of the same. At any 
elegans King. The shell figured under this name 18 
certainly a distinct species, and not a variety of the elegans, since 
a fine series of specimens show it to be exceedingly constant * 
all its characters (which are well represented in Prof. Geinitz’s 
figure), while it differs from that species not only in never at 
taining one-tenth the size of larger examples of that shell, but 
in being much narrower and more distinctly truncated behind, 
as well as in having its umbonal slopes always sharply k 
Its umbones are also more elevated. 
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excepting that it is a little more compressed, and has i 
and rounded, and its posterior margin more distinctly, and —_ 
that from Illinois, and those figured from Russia, as three close! 
allied, but distinct oa That under consideration is sxe 
ingly constant in all its characters (as shown in a good series % 
Specimens) and exhibits no tendency to the variations of yes 
mee be presented amongst the different individuals of S. 4° 
* The beds at Atchison, Kansas, hold a low. stratigrapical postion than the 
é Iceni the mouth of Platte river, referred by : Marcou to the Moustsia 
