C. Wachsmuth—Structure of Paleozoic Crinoids. 121 
either side, the inner rows of which join in the middle, inter- 
ock with each other, and form an apparently solid covering. 
The outer plates which are attached to the arm-joints are 
toward the upper end of the arms placed partly upon the edges 
of the joint, pat nearer the calyx rest wholly against the edges 
of the upper part of the ventral furrow. They are longitudi- 
nally arranged, partly hidden from view by the inner plates. 
The visible part is quadrangular, with a narrow tooth-like pro- 
jection toward the lower end of each plate, which is directed 
inward and slightly downward as a sharp, elongated process, 
and forms a support for the inner plates. The inner plates 
are elongated triangular, resting with their shorter sides against 
the inner faces of the outer series, and, between the tooth-like 
extensions, overlapping them with their beveled lateral edges, 
im such a manner that each plate exteriorly fits in and fills 
the space between each pair of similar triangular plates on the 
other side. The two longer sides interlock with corresponding 
sides of similar plates of the opposite row, their sharp angles 
or apices meeting the sutures between the opposite quadrangu- 
lar plates. At each of these points of juncture, just beyond 
the apex of each triangular piece, on either side of the furrow, 
there is a little pore, which evidently communicates with the 
mner channel. There are six sets of plates to each arm-joint, 
all the plates being imbricated from the lower side upward,— 
that is, the lower ones lap slightly the edges of the upper ones 
—thus facilitating the movements of the sms. 
n describing the skeleton below the vault, I suggested that 
trans- 
? 
the tubes were a continuation of the erm furrows. A tran 
