EEPORT ON THE CRINOIDEA. 395 



several recent researches have supplied further cogent reasons for rejecting the homologies 

 which Loven seeks to establish between the dorsocentral of an Urchin or Starfish and the 

 uuder-basals of a dicychc Crinoid. 



Six years ago the numerous modifications of tile apical system which arc presented 

 by Asterids and Ojjhiurids had received comparatively little attention ; and I was 

 therefore led to regard the under-basals of Encrinus, Extracrinus, and of the Palaeozoic 

 Crinoids as " additional elements which occur in the apical system of some Crinoids, 

 while they are unrepresented in other members of the order and in the other Echino- 

 derms."^ Four years later, however,^ I was able to show that the apical system of 

 the young Amphiura squamata, which had been recently described by Ludwig,' 

 corresponded precisely with that of Marsupites, the type which was first selected 

 by Loven for comparison with Salenia. Both in Amphiura and in Marsupites there 

 is a central abactinal plate representing the dorsocentral of an Urchin. Next to this 

 come, not the interradial plates corresponding to the genitals of an Urchin and the 

 basals of Cyathocrinns, as Loven formerly supposed,* but a ring of radially situated 

 plates which correspond to the under-basals of Cyathocrinus, but are not represented 

 at aU in the apical system of an Urchin, as at present known. Outside these come the 

 interradial basals (genitals) and then the radials (oculars). Ludwig discovered that 

 the latter remain on the disk of Amphiura, and are not carried away from it by the 

 growing arms as had been generally supposed. 



Having discovered, as I believed, the homologues of the under-basals of a Crinoid 

 in a larval Ophiurid, I naturally began to seek for them in the adult members of 

 the class ; and it soon appeared that they were represented in the rosette of primary 

 plates which occupies the centre of the disk in certain species of Ophioglypha, 

 Ophioceramis, OpMomusium, and Ophiozona.^ At the same time two important 

 discoveries bearing on this question were made by Sladen.'' (1) The radial plates 

 of the larval Asterid remain on the disk, like those of the Ophiurid, and are not 

 carried outwards by the growing arms, as was formerly supposed. (2) In the late larvae 

 of Zoroaster fulgens, Asterina gihhosa, Asterias ruhens, Asterias glacialis, and other 

 species, the so called genital plates ( = basals of a Crinoid) are separated from the 

 dorsocentral by a ring of radial plates which occupy exactly the same position as the 

 under-basals of Marsupites, and the corresponding plates in the Ophiurids mentioned 



I Qmrt. Journ. Mier. Sci., 1878, vol. xviii., N. S., p. 374. 2 ji^d^ i882, vol. xxii. p. 380. 



3 Ziir Entwicklungsgeschichte des Ophiureiiskelettes, Zeitschr.f. iciss. Zool.,BA. xxxvi. 1882, pp. 181-200, Tafn. x., .\i. 



* Lovin appears to have been so far influenced by my criticisms on his comparison of the radially placed 

 imder-basals of Marsupites with the interradial genitals of Salenia that he makes no further reference to the former 

 type, although in his earlier " i^tudes " he laid great stress upon its resemblance to Salenia. This is unfortunate, 

 because the presence of a dorsocentral in Marsupites, as well as of under-basals homologous with those of Cyathocrinm, 

 proves conclusively that the latter cannot represent the dorsocentral of Marsupites, and therefore of Salenia, as Lov^n 

 formerly supposed. 



5 Quart. Journ. Micr. Sci., 1884, vol. xxiv., N. S., p. 11. " Ibid., pp. 29-34. 



