158 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
there are resting upon the radials what we take to be plates of the tube. 
These plates, which are crescent-shaped and extremely heavy, are longitu- 
dinally arranged, and pass up to near the top of the arms. The relation of 
these plates is not altogether clear, but they probably represent the heavy 
and solid plates of Jocrinus, which constitute the ridge along the posterior 
side of the sac; and we believe that the open groove at the anterior side was 
in the animal filled, as in the case of Jocrinus, by small disk plates, which 
may or may not have been perforated. This interpretation seems to us 
the most probable, and upon the strength of it we have placed both families 
under the Fistulata. 
Bather’s definition of the Monocyclica is short: ‘Inadunata with no 
infrabasals.” But notwithstanding its brevity it meets with two exceptions: 
Cupressocrinus and Myrtilocrinus, which Bather referred to the Monocyclica 
with some doubt; both have an infrabasal disk. It will not help the matter 
to say that the plate in both groups is a top stem joint (centrodorsal), for the 
condition of the plate in Cupressocrinus, as well as in Myrtilocrinus, is very 
different from that under which the centrodorsal occurs in the Apiocrinide, 
Comatulz, and Ichthyocrinidew. Wherever that plate occurs, it is in dicyclic 
Crinoids, and the infrabasals are fused with it. When the fusion is complete 
there appears in place of the infrabasals a vacant space at the inner floor of 
the calyx between the basals; nothing of which is found in these two genera. 
Besides, the plate does not rest against the outer faces of the basals, as it 
should do if it were a top stem joint, but against their inferior faces, like 
the infrabasals of true dicyclic Crinoids. 
Mr. Bather alludes to a structural peculiarity, which he thinks has “more 
weight in the classification than the varying extent of tegminal develop- 
ment.” He says: “It will be seen from the ensuing remarks on Pisocrinus, 
Calceocrinus and Herpetocrinus, that a very large number of Inadunata Mono- 
cyclica closely resemble one another, either in the horizontal bisection of 
certain radials, a character which in Dicyclica is entirely confined to the 
right posterior radial, or in the greater development of certain other radials.” 
He overlooks the dicyclie Tribrachiocrinus, which has three compound radials, 
and we find on examining the genera which he referred to the Monocyclica, 
that among the twenty-four only eight have three compound radials, and 
sixteen have not. Among the latter there are three with two compound 
radials, Anomalocrinus, Ohiocrinus, and Baerocrinus,* and three with a single 
* In the latter, as we understand the structure, only the inferradials became developed, but not the arm- 
bearing section. 
