244 PROCEEDINGS OF THE ACADEMY OP [1879. 



It is now a very important fact that these two rings of plates . 

 the first radial s and the interradial set of plates next below them 

 are the only ones which are found in all Crinoids from the 

 earliest geological ages to the present time. It thus appears that 

 the evidence derived from the embryology of the Pentacrinoid, 

 and the observed mode and order of development in the Paleo- 

 crinoids during individual life, is fully and beautifully confirmed 

 by the geological history of Crinoids. 



All this evidence seems to us to be conclusive, and to prove 

 satisfactorily that the two rings of plates regarded by Carpenter 

 as genitals and oculars, are the fundamental parts in the aboral 

 side of the calcareous skeleton, and that the subsequent orders of 

 radials and interradials are to be considered as supplementary to 

 them, and as the products of growth in the individual and develop- 

 ment in geological time. 



Our conclusions being thus in harmony with Prof. Carpenter's 

 views, we think it both logical and expedient to adopt his terms, 

 and call the first ring of plates below the radials " basals" in all 

 cases, and the second ring below, or the proximal plates when 

 there are two rings, " underbasals," thus discontinuing the term 

 " subradials'' altogether. 



We cannot, however, agree with Carpenter in supposing, as he 

 does, p. 374, that the underbasals have no representative in the 

 apical S3'stem of other Crinoids or Echinoderms. We incline to 

 the opinion of Agassiz, Loven, and others, that the}- are homolo- 

 gous with the central disc or su banal plate of the Echini, and 

 with the centro-dorsal plate of Gomatula. In the paleozoic genus 

 Jgassizocrinus, which was evidently pedunculate in its earlier 

 stages, but became a freefloater when mature, we find in the proxi- 

 mal ring in young specimens five plates with a central perforation 

 in the disc, and a distinct articulating scar for the attachment of 

 the column. In the free stages, however, every trace of the cen- 

 tral foramen and of the columnar attachment has disappeared, and 

 in most of the specimens not even a vestige of the sutures 

 formerh/ existing between the plates can be detected. In some 

 they can still be faintly observed, but only near the edges upon 

 which the succeeding plates rest, and not in the median portion of 

 the disc. Another example of this is seen in Edriocrinus (New 

 York Geol. Rep., vol. iii. pp. 119-20) in which the bodies are 

 when young attached to each, other or to other solid bodies, and 



