SUPPLEMENT. 



SQ9 



in the absence of the obscure creuulations 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. 



NoTB. Tn 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 Iludson-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. 



tlic game specimen, or from the same flgvire tliroughout, by subsequent authors; and the original appears 

 to have been deprived of tlie clieeks, 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. 



[ PALiEONTOLOOT III.] 67 



