SUPPLEMENT. 
539 
in the absence of the obscure crenulations or inequalities upon the limb of the 
pygidium, which is regarded by Pictet as important. The number of segments of 
the thorax, if a constant character, seems much more important, and furnishes a 
more marked feature for the separation from Olenus. 
Peltura holopyga. 
Geological position. In the shales of the Hudson-river group. 
Note. In addition to the evidence heretofore possessed regarding the position of the shales con¬ 
taining the Trilobites, I have the testimony of Sir W. E. Logan that the shales of this locality are in 
the upper part of the Hudson-river group, or forming a part of a series of strata which he is inclined 
to rank as a distinct group above the Hudson-river proper. It would be quite superfluous for me to 
add one word in support of the opinion of the most able stratigraphical geologist of the American 
continent. 
the same specimen, or from the same figure throughout, by subsequent authors; and the original appears 
to have been deprived of the cheeks, the frontal limb, and the posterior cephalic spines. The eye-tubercle, 
or the palpebral lobe, having collapsed as in our specimen, gives but a partial representation of the entire 
animal. 
[ Palaeontology III.] 
67 
