304 P. HEEBEET CAEPENTEE. 



and I expressed my belief in 1882 l that they respectively 

 represent the under-basals and basals of the dicyclic Crinoids 

 (fig. ii, 2, 3). Two years later I pointed out the presence of 

 this dicyclic base in various adult Ophiurids 2 ; while the 

 important discovery was announced by Sladen that it likewise 

 occurs in many Asterids, both larval and adult, and also that 

 in this group, just as in the Ophiurids, there are primary 

 radial plates which remain on the disc while the terminals are 

 carried outwards on the growing arms. 3 



These primary radial plates of Asterids and Ophiurids, 

 including Amphiura, were homologised by both Sladen and 

 myself with the first radials of the Crinoidea, the correspond- 

 ence of which with the ocular plates of the Urchins had been 

 long ago pointed out by Agassiz, Loven, and others. No one 

 had questioned this latter comparison, and it appeared equally 

 indisputable that the primary radials of Amphiura were also 

 homologous with the ocular plates of an Urchin, despite the 

 relation of the latter to the eye-spot, a relation which is not 

 characteristic of the primary radials in either of the three 

 groups of brachiate Echinoderms. 



The subject has been lately reopened by Fewkes, 4 who 

 says : — 



" The question which plates in the young Amphiura cor- 

 respond to the oculars of sea-urchins, assumes a new phase in 

 the light of what we know of the permanent retention of the 

 radials in the abactinal hemisome of the body of Amphiura, 

 and the relation of the terminals to the primitive tentacle. 

 Now that we know that the primary radials of Amphiura are 



1 " Notes oil Echinoderm Morphology," No. V : "On the Homologies of 

 the Apical System, with some Remarks upon the Blood-vessels," ' Quart. 

 Journ. Micr. Sci.,' 1882, vol. xxii, New Ser., p. 380. 



2 " Notes on Echinoderm Morphology," No. VII : " On the Apical System 

 of the Ophiurids," 'Quart. Journ. Micr. Sci.,' 1884, vol. xxiv, New Ser., pp. 

 4, 11. 



3 " On the Homologies of the Primary Larval Plates in the Test of Brachiate 

 Echinoderms," 'Quart. Journ. Micr. Sci.,' 1884, vol. xxiv, New Ser., pp. 

 29, 34. 



4 Loc. cit., p. 124. 



