REPORT ON THE CRINOIDEA. 395 
several recent researches have supplied further cogent reasons for rejecting the homologies 
which Loyvén seeks to establish between the dorsocentral of an Urchin or Starfish and the 
under-basals of a dicyclic Crinoid. 
Six years ago the numerous modifications of the apical system which are presented 
by Asterids and Ophiurids had received comparatively little attention; and I was 
therefore led to regard the under-basals of Encrinus, Extracrinus, and of the Paleozoic 
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 Lovén 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 Cyathocrinus, as Lovén formerly supposed,* but a ring of radially situated 
plates which correspond to the under-basals of Cyathocrinus, but are not represented 
at all 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, Ophiomusium, 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 larvee 
of Zoroaster fulgens, Asterina gibbosa, Asterias rubens, 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 Marswpites, and the corresponding plates in the Ophiurids mentioned 
1 Quart. Journ. Micr. Sci., 1878, vol. xviil., N. S., p. 374. 2 Tbid., 1882, vol. xxii. p. 380. 
3 Zur Entwicklungsgeschichte des Ophiurenskelettes, Zeitsclr. f. wiss. Zool.; Bd. xxxvi. 1882, pp. 181-200, Tafn. x., xi. 
* Lovén appears to have been so far influenced by my criticisms on his comparison of the radially placed 
under-basals of Mursupites with the interradial genitals of Salenia that he makes no further reference to the former 
type, although in his earlier “ Btudes” 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 Cyathocrinus, 
proves conclusively that the latter cannot represent the dorsocentral of Marsupites, and therefore of Salenia, as Lovén 
formerly supposed. 
5 Quart. Journ. Micr. Sci., 1884, vol. xxiv., N. 8., p. 11. 6 Ibid., pp. 29-34. 
