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. meeki, 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: — Cal, ymene 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 
clintont Vanuxem. 
Lnocalymene clintoni, 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, 
pl. A 66, f. 5a), and is from the Clinton shale at Clinton, Herkimer Co., 
1 Be 
