CRUSTACEA. 
123 
“ C. marginalis. Buckler, with a broad margin ; eyes large, semi-oval; middle 
lobe entire, convex, smooth abdomen.” 
'■'■Locality. Near Ithaca, in a boulder. This has a much less prominent 
front than the Rowi, a deeper groove between the eye and middle lobe, and 
the tubercle which nearly joins the lower angle of the eye is much smaller.” 
It was subsequently ascertained that the boulder referred to by Mr. Conrad, 
was a mass of the Tully limestone, which had been transported many miles south 
of the outcrop of that formation. For this reason the species of Pro'etus which 
has been frequently found in the outcrops of this rock upon Seneca and Cayuga 
Lakes, in Onondaga county, and elsewhere, was regarded in the published de¬ 
scriptions of 1861 and 1862 {vid. he.), as probably specifically identical with Mr. 
Conrad’s original. This reference was without doubt correct, but the more com¬ 
plete material illustrating this fossil and its allies in adjoining formations, which 
has accumulated since the publication of these descriptions, has afforded con¬ 
clusive evidence that P. marginalis, Conrad, is identical in every specific detail 
with P. Rowi, Green. 
The points of difference in these forms, as stated in the description quoted 
above, depend solely upon the condition of preservation of the specimens. As 
the individuals of P. marginalis occurring in the State of New York are pre¬ 
served in limestone, the surface has more nearly retained its normal rotundity, 
and the glabella is less extended anteriorly than in the usually somewhat flat¬ 
tened examples of P. Rowi from the Hamilton shales. The specimens from 
the Tully limestone show that the glabella encroaches slightly upon the frontal 
margin, as in normal examples of P. Rowi. 
The depth of the groove between the eye and the glabella depends entirely 
upon the degree of flattening of the specimen; and the size of the occipital 
lobe varies with the absence or retention of the crust. 
After a careful examination of all the representatives of P. marginalis at 
hand, it seems impossible to associate any characteristics by which it can be 
distinguished as even a variety of P. Rowi, and the foregoing description of the 
latter species will apply in every respect to Mr. Conrad’s P. marginalis. 
This fossil occurs in the Tully limestone, in intimate association with Pha- 
