TRENTON LIMESTONE. 81 
Genus SCHIZOCRINUS. 
[ Greek, oy:o, to cleave; in allusion to the cleft or double interscapular plates.] 
Character. Pelvis composed of five pentagonal plates ; first costals five, joining at their 
lateral edges ; second costals five, separated by a hexagonal intercostal plate, which rests 
upon the upper lateral edges of the lower costals ; scapular and arm-plates five, hexagonal, 
the lower side curved and fitting the concave upper edge of the plates below ; hand-joint 
double or bipartite, as also the interscapular or interbrachial plates; hands and fingers 
regularly bifurcating. 
This genus, in its general features, bears a close resemblance to some species of the 
Cyatuocrinus ; but the greater number of series of plates, and the duplicate character of 
the interscapular plates, is sufficient to separate it from that genus. It bears considerable 
resemblance in its characters to the Dimerocrinites of PuiLuips, presenting nearly the same 
deviations from Cyathocrinus which that genus does from Actinocrinites. 
122. 1. SCHIZOCRINUS NODOSUS (x. sp.). 
Pu, XXVII. Figs. 1 a-p. 
Body cupshaped, obtusely pentagonal, spreading somewhat abruptly from the column ; 
arms short ; fingers in ten pairs, fimbriated ; column round, composed of joints of unequal 
thickness and diameter, the larger ones furnished with side-arms ; surface of the joints 
deeply striated in radii, which give a serrated appearance to the edges of the plates. 
This species is perhaps the most abundant of any in the Trenton limestone, though 
usually seen only in fragments of columns. The column, as in many other species, varies 
considerably in appearance at different distances from the body ; which characters require 
to be considered, in order to recognize the same when found in small fragments. The thin 
upper plates of the column are about equal in thickness and diameter ; and for some distance 
below this the column is composed of alternating larger and smaller plates, the larger ones 
being thicker, and gradually becoming nodulose on their margins. In tracing the column 
downward, there is a gradual increase in number of the smaller plates between the larger 
ones ; the second stage being two, the third three, and the fourth four; and, in the mean 
time, the larger plates become furnished with side-arms. When the number of intermediate 
plates between the arm-plates reaches the number of five, the central one shows a tendency 
to thickening and enlargement, and does, at least in a great number of instances, assume 
the character of the thicker armed plates, which finally become equally developed with the 
others. This change in the character of the column at different distances from the body 
presents a great variety of aspect, and, when examined in fragments, is liable to lead the 
student astray, by inducing him to refer fragments of the same species to different ones. 
In weathered specimens of this column, the edges present a beautiful serrated appearance, 
from the elevated striz upon the plates of the column joining together, the elevations of 
one filling the depression in the other. The side-arms of the larger joints are rarely seen of 
any considerable length, the bases ‘veing all that usually remain of them. 
| PanzonrTotoey.] 11 
