1879.] NATURAL SCIENCES OF PHILADELPHIA. 239 



Prof. P. Herbert Carpenter, in a valuable paper (Quarterly Journ. 

 Microscop. Sci., vol. xviii (new series), p. 351), on the "Oral and 

 Apical Systems of the Eehinoderms," undertakes to determine the 

 homologies between that system of plates in the calcareous skele- 

 ton of the Echini known as apical plates, and certain parts of the 

 calyx of Crinoids, both recent and fossil. He considers the basals 

 of recent Crinoids to be homologous to the genital plates, and the 

 radial s to the ocular plates of the Echini, and he traces the homo- 

 logy to the Paloeocrinoidea, in respect to which, however, he ad- 

 vances the opinion that the first ring of plates resting upon the 

 upper stem segment, which have heretofore been nominated 

 "basals" are in many types not basals at all. He regards the set 

 of plates which lie next below the radials as the true "basals," no 

 matter whether they rest directly upon the stem, as in Platycrin us, 

 or are separated from it by another ring of plates, as in Cyalho- 

 crinus; so that the "subradials" of most American authors, or 

 "parabasals" as they are generally termed in Europe, are "basals" 

 according to his view. The lowest or proximal ring of plates, in 

 types having "subradials," he calls "underbasals," and these he 

 believes to be unrepresented in the other types of Crinoids and all 

 other Eehinoderms. The central plate of the apical system, re- 

 presented by the central disk or subanal plate of the Echini, is 

 thought by Carpenter to be the homologue of the terminal joint 

 at the base of the stem in all pedunculated Crinoids, and in the 

 Pentacrinoid larva of Comatula, and of the central plate in Mar- 

 supite*. 



In several respects these views conflict with those of A. Agassiz 

 and Loven, who regard the subanal plate of the Echini as the 

 homologue of the centro-dorsal plate of Comatula; and both these 

 as representing the "basals" of the Crinoids, by which term they 

 designate the first ring of plates above the stem in all types. They 

 consider the single plate in the apical system of the Echini as the 

 equivalent of the basalia of the Crinoids metamorphosed into one. 

 Carpenter's reasoning in regard to the basal plates is, that, as 

 the genitals in the Echini, and the basals in most Paleocrinoids, 

 which are generally considered to be their homologues, are situated 

 interradially with regard to the general symmetry of the tyxly, 

 we must expect to find the genitals in Paleocrinoids in the same 

 relative position ; and that in forms like Cyathocrinus, which have 

 two rings of plates below the radials, the lower or proximal plates 



