RAYMOND: NEW AND OLD SILURIAN TRILOBITES. 29 



The pygidium is the most characteristic portion of the animal. 

 The axial lobe is narrow, well defined, and has rings. The pleural 

 lobes show four pairs of narrow ribs, without impressed line, which 

 reach only halfway to the margin. The fourth of the four pairs are 

 very faint and short. Each pleural lobe is thus divided into a small 

 triangular ribbed portion near the axial lobe and a much longer smooth 

 portion below. This pygidium presents the greatest possible contrast 

 to C. niagarensis, in which the ribs are more conspicuous near the 

 margin than near the axial lobe. The peculiarities of the pygidium 

 have doubtless been noticed before, and probably have been explained 

 as due to the state of preservation, the specimens all being internal 

 casts. Internal casts of either cephala or pygidia of trilobites are 

 practically always less and not more smooth than the exteriors, how- 

 ever, and cleaned interiors of C. senaria, C. breviceps, and C. meeJci, all 

 show that Calymene follows the general rule. Calymene celebra shows 

 a halfway stage to what is achieved in C. clintoni Vanuxem, namely, 

 a pygidium with smooth pleural lobes. The latter species is too far 

 removed from the Calymenes with typical ribbed pygidia to be in- 

 cluded in the same genus. 



Formation and locality: — - Calymene celebra is common in the 

 Niagaran of the Chicago district in northern Illinois, in the same 

 portion of the Silurian in southeastern Wisconsin, and also near 

 Madison, Indiana, and Eaton, Ohio. 



LiocALYMENE, gen. nov. 



Calymeninae (as distinguished from the Homalonotinae) with 

 distinct glabella, three pairs of glabellar lobes, narrow thorax, pygidium 

 with ringed axial and smooth pleural lobes. Type, Hemicrypturus 

 clintoni Vanuxem. 



Liocalymene cJintoni, in perfect preservation, appears to be an 

 exceedingly rare fossil. The single specimen in the M. C. Z. is in 

 about the same condition as that figured by Hall (Pal. N. Y., 2, p. 298, 

 pi. A 66, f. 5a), and is from the Clinton shale at Clinton, Herkimer Co., 

 N. Y. 



