158 THE CEmOIDEA 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 locrinus, 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 locmius, 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: ^^nadunata with no 

 infrabasals." But notwithstanding its brevity it meets with two exceptions : 

 Gupressocrimis and M^rtilocrinus, 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 Apiocrinid^, 

 Comatulae, and Ichthyocrinidse. 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 Fisocriiius, 

 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 dicyclic Trihrachiocrinus, 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, Ohiocriiius, 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. 



