ORAL AND APICAL SYSTEMS OF THE ECHINODERMS. 365 



crinus, and Comatula (figs, i, iv, v, 4, 4.) These, as pointed 

 out by Loven, are homologous with the ocular plates of 

 Echini (fig. n, 4, 4),and not with the genitals (fig. ii, 3, 3), 

 for the latter represent the basals of Pentacrinus, Bncrinus 

 (fig. IV, 3, 3), and Comatula (figs, i, v, 3, 3) which Loven, 

 reasoning from the calyx of Marsupites (fig. iii, 2, 2), has 

 wrongly termed costals. 



Consequently, Loven's suggestion that the term '' Costals" 

 should be used as a general expression to designate the inter- 

 radial plates of the apical system (figs, i — ix, 3, 3) cannot 

 be regarded as satisfactory. In the genus Cyathocrinus only 

 (fig. vi) did Miller use it in this sense, as he generally em- 

 ployed it to designate the true radial plates (figs, i — vii, 

 IX, 4, 4), situated upon, and alternating with, those plates 

 which Loven would call costals. But in Marsupites Miller 

 gave this name to the innermost set of radial plates (fig. iii, 

 §, 2), which are absent from the Apical System of many 

 Crinoids (in the widest sense of the term) and of all the other 

 Echinoderms. In either case, however, Loven's use of the 

 term costals is somewhat inappropriate. 



It should be noticed here that Loven is not the first natu- 

 ralist who has made use of Marsupites in tracing resem- 

 blances between the Crinoids and the other Echinoderms. 

 As long ago as 1851 Major Austin^ suggested that the five 

 genital plates of the Urchins might be regarded as collec- 

 tively representing the dorsocentral plate of Marsupites, and 

 of the Crinoids generally. He used this name to designate 

 the pelvis or basis, and thus compared the genital plates of 

 the Urchins to the basals of the Crinoids, which is pre- 

 cisely the view advanced above. With regard to Marsujiites, 

 however, I diflfer from Major Austin, for I have already 

 explained that I cannot agree with the generally accepted 

 view that the central disc oi Marsupites represents the compo- 

 site basis of the other Crinoids. Two questions, therefore, 

 have now to be determined, first. What is the true nature 

 of the central disc of 3Iarsupites ? and second, Which of 

 the plates in its calyx represent the basals of Pentacrimcs 

 and the other Articulata ? 



The first question will be considered later, while the 

 second can, I think, be answered in but one way. The 

 basals of Pentacrinus, Encrinus, and Comatula (figs, i, iv, 

 v, 3, 3,) are interradial and lie immediately beneath the 

 radials (figs, i, iv, v, 4, 4), which rest upon them and 



^ " On the connectiou between the CrinoidecB and the Echinodermata gene- 

 rally," ' Annals and Magazine of Natural History.' Second series, vol. viii, 

 pp. 285-289. 



