Bibliographical Notices. 281 



but also of the Urchins and Stellerids, with regard to the abactinal 

 centre is a very definite one ; and if plates which typically occur 

 inside the circle of dome-radials, between them and the actinal 

 centre, are to be regarded as homologous with abactinal plates, which 

 are generally outside, and only very rarely form part of the circle 

 of calyx-radials *, the word " homology " would almost cease to 

 have any meaning in Echinoderm morphology. 



There is another view of the homologies of the proximals, which 

 was suggested by the writer in 1879, viz. that they represent the 

 oral plates of Xeocrinoids. Messrs. Wachsmuth and Bpringer admit 

 that these orals are the actinal representatives of the basals, as was 

 pointed out by Gcitte ; and they thus give additional support to the 

 suggested homology between the orals of Neocrinoids and the 

 proximals of Palajocrinoids, which last they formerly regarded as 

 corresponding to the basals of the abactinal side. They bring 

 several objections to this view, some of which are well founded ; but 

 it does not appear to us to involve anything like such serious incon- 

 sistencies as their own latest theory, which necessitates an homology 

 between one set of plates outside the circle of abactinal radials and 

 another set inside the circle of actinal radials ! 



Their objections will be fully discussed by the writer when he has 

 finished the somewhat absorbing systematic work on which he is 

 at present engaged. But two of them deserve notice here. In 

 more than one place (pp. 36, 54, 58) the authors object to the theory 

 which regards the proximals as homologous with the orals, because 

 there are only five of the latter but six of the former plates, the 

 posterior one being divided into two parts, usually by the anal 

 system. This is a curious objection to come from those who tell us 

 that these very six proximals are the actinal representatives of the 

 five calyx-interradials of Cijathocrinus and the Elastoids. On the 

 same principle they must deny the homology of the six interradials 

 of Ela'acrinus with the five which occur in other Blastoids ; for the 

 posterior one is divided into two parts by the aual plate. The same 

 difiiculty occurs with respect to Glyptaste)-, Ei(criaus, Dori/crinus, 

 &c., about which we are told, on p. 13 of Part II., that " the first 

 true interradial in the posterior area is divided, and is represented 

 by two smaller plates, separated by a special anal plate.'' But 

 unless they deny the homology of the six interradials of Ghjptaster 

 and Ekencrinus with the five of Cyathocrmus their objection to a 

 theory which homologizes " six jiroximals with five orals " loses all 

 its force ; and we do not think that they are prepared to go so far 

 as this. 



In every Neocrinoid the anus is outside the ring of oral plates, 

 and this has always been felt to be one of the chief objections to the 

 theory that the proximals are orals ; for plates belonging to the anal 

 system usually enter into the ring of proximals. But we may point 

 out that the mouth-opening, which also serves as anus in Ophiurids 

 and in many Asterids, is within the circle of orals, and that the 

 anal system of a regular Urchin is situated within the ring of basals 

 which are the admitted abactinal homologues of the orals ; while the 



* As in the Rhodocriuidae and the recent Thaumatocrinus. 



