ORAL AND APICAL SYSTEMS OF THE ECHINODERMS. 359 



point to. which I shall shortly return. The ocular plates 

 of the Urchins (fig. ii, 4, 4) are indicated by Loven as homo- 

 logous with the third series of plates in the Marsupites 

 calyx, namely^ the radials (fig. in, 4, 4), a determination 

 in which I entirely concur. 



Miiller/ De Koninck/ and Schultze^ regarded the central 

 disc of Marsupites as the basis, and supposed the plates of 

 the second ring [interradiaV) to represent the ordinary 

 "parabasals'^ or '^subradials" of Cyathocrinus, Poteriocrinus, 

 Hhodocrimis, and other Palaocrinoidea. De Koninck spe- 

 cially mentioned the fact of their alternating with the radials 

 so as to be interradial in position. FolloAving Miiller, he 

 spoke of the proximal ring of plates in Marsupites, inter- 

 vening between the true parabasals (subradials) and the 

 central disc, as a second series of parabasals, constituting a 

 new element in the calyx peculiar to this genus. Loven, 

 however, for no apparent reason, takes a precisely opposite 

 view, and regards the plates of the first ring as the first or 

 true parabasals, those of the second ring being " parabasals 

 of the second order," which are unrepresented in the Urchins 

 and in the Palaeozoic Crinoids. 



Having compared the apical system of the Urchins with 

 the calyx of Marsupites, Loven further proceeds to trace out 

 its homologies with the calyx of the Crinoids generally, and 

 especially of the older and pedunculate forms. 



I regret to state that I am unable to agree with him in 

 many of these comparisons, partly because some of them are 

 based upon views which I believe to be erroneous, and partly 

 because he does not appear to have altogether understood 

 some of the eccentricities in Miller's terminology. 



In the first place, the hasis in the nomenclature of J. 

 Miiller, d'Orbigny, De Koninck, and Schultze (= pelvis, 

 Miller), or the centrodorsal (and not dorsocentral, as Loven 

 quotes it) of De Blainville, is, I am firmly persuaded, in no 

 way comparable to the central disc of the Urchins and of 

 Marsupites, These, like Loven, 1 regard as homologous 

 with one another, but I cannot follow Miiller and most sub- 

 sequent writers in considering the central disc of Marsupites 

 as representing five closely anchylosed basals. Although 

 Miller,^ the first naturalist who analysed the calyx oi Marsu- 

 pites, spoke of this central disc as the pelvis ( = basis), yet 

 he also suggested that it might not be of this nature, and 



^ ' Pentacrinus,' loc. cifc., p. 32. 



2 Loc. cit., p. 67. 



' Loc. cit., p. 4 (116). 



* ' A Natural History of the Crinoidea/ pp. 137—139. 



