106 PROCEEDINGS OF THE ACADEMY OF [1887. 



plates rest directly against the calyx interradials, that ou the poste- 

 rior side being represented by two small plates with the anus between 

 them" while there is a more or less tubercular ring of radial dome 

 plates outside them. These proximal dome jjlates thus correspond 

 exactly to the orals of /Syvibathocrinus ajd Haplocrinus, covering in 

 the peristome and resting against the calyx plates, which in the 

 Platycriuus are the interradials, and not the upper edges of the ra- 

 dials, as in the simpler forms"; and on p. 171 : "I cannot therefore 

 see what other view can be taken of the proximal dome plates which 

 immediately surround the orocentral, than to regard them as orals, 

 i. e., as the actinal representatives of the basals, like the correspond- 

 ing plates in Symbathocrinus. If this he admitted, it follows that the 

 proximal dome plates of all Platycrinidae, Actinocrinidae and Rho- 

 docrinidae are also homologous with the orals of Neocrinoids." 



These conclusions perhaps might be well enough, if such a thing 

 as an orocentral had been established ; but unfortunately this is not 

 the case. Neither are the plates in Symbathocrinus of which he 

 speaks as "the orals," in our opinion, anything but proximals, and 

 hence all conclusions based thereon, to say the least of it, are inex- 

 pedient and rash. It is somewhat surprising that Dr. Carpenter, 

 although his whole theory is actually based upon his hypothetical 

 "orocentral," gives such a meagre account of it. In the Challenger 

 Report, in introducing it on p. 158, he devotes to it only a few lines. 

 Referring to the small central plate of Haplocrinus, he says: "This 

 plate is one of considerable importance in its morphological relations. 

 In accordance with the views which I have expressed elsewhere, I 

 believe it to be the representative on the actinal side, or left larval 

 antimer, of the dorsocentral plate which is developed in the center 

 of the right antimer or abactinal side of Urchins, Stellerids, and 

 Crinoids." And on pp. 159 and 170, in pointing out its relations 

 to the proximals, he calls the plate the orocentral, and speaks of it 

 as a single plate. That is all Dr. Carpenter had to say about it, 

 and probably all that could be said, for such a plate has been here- 

 tofore unknown in Echinoderm morphology. 



We do not deny that the so called dorsocentral of Urchins and 

 fitellerids is represented in the Comatula larva by the terminal plate 

 of the stem, but we see no good reason to postulate from this a 

 similar plate in the oral center. There are at the abactinal side 

 frequently also underbasals, which on the same principle should be 

 represented orally, but nothing is known of them. Why should 



