70 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



in the calyx, were treated by us in the same way as the Camerata. Schultze, 

 however, described Taxocrinus as having but one radial, in which he was 

 correct from his standpoint, for the succeeding plates seem to be united 

 among themselves, and with the radials by loose suture or a sort of rudimen- 

 tary articulation. Carpenter described Pentacrinus- and the Comatulse, which 

 are in a similar condition to the Ichthyocrinidaa, as having three radials in 

 all cases, whether the plates are enclosed by perisome or not, and he distin- 

 guished the rami as primary, secondary, and tertiary arms. According to 

 him, Rhizoerinus Rawsoni, with ten arms, has three radials ; while R. lofotensis, 

 like Cupressommis, Pisocrinus, and all Crinoids with but five arms, have one 

 radial, followed by brachials. He thus made the second plate of the ray a 

 second radial in the former, and n. first hrachial in the latter, giving to parts 

 which are undoubtedly homologous different appellations, while distinct parts 

 were thrown together. The methods of treating these plates heretofore 

 adopted were not only empirical, but inconsistent with the principles of 

 morphology; and the want of uniformity among the different writers, 

 respecting the terms, must have been perplexing to the student when con- 

 suiting their works. 



In 1881,^ and again in 1885,t we expressed the opinion that the arms 

 fundamentally begin with the second plate of the ray, and that all Crinoids 

 have but one ring of radials. In support of this we stated that only the 

 lower ring could be homologized with the oculars of other Echinoderms ; 

 that in the simpler form — the Inadunata — the arms were free from the 

 (first) radials, and that in the remaining groups the lov>^er arm plates were 

 incorporated gradually in palaeontological time. We refrained, however, at 

 that time from changing the terminology, finding it convenient for purposes 

 of description to continue the old terms. 



Our interpretation of the plates was accepted by Carpenter in 1884^ 

 who confirmed it by the developmental history of the plates. The " outer 

 radials," he says, " commence as imperfect rings, which soon become filled up 

 with lengthening fasciculated tissue, just as is the case with the stem joints 

 and later brachials;" but "the first radials, like the basals and orals, com- 

 mence as expanded cribiform films." He further alluded to the fact that the 

 so-called primary radials of Metacrimis are pinnule-bearing, — a thing which 

 we have observed in exceptional cases among the Poteriocrinidse also. 



* Revision, Part IT., p. 10. f Ibid., Part III.p. 12. 



% Ciiallenger Rep. on the Stalked Crinoids, p. 48. 



