4 Dr. P. H. Carpenter on the 



central plate of the Echinoderm apical system has been 

 repeatedly noticed by us botli and also by others under the 

 name "" dorsocentral ; " and zoologists have been wai'ned 

 again and again not to confuse it with the enlarged top stem- 

 joint in the stem of many Crinoids, for which, in the case of 

 Comattda, Miillcr and his successors had employed the name 

 " centro-dorsal." Early in 1887 Duncan and Sladen *, 

 writing on the morphology of the Saleniida3, frequently re- 

 ferred to the so-called sur-anal plate of Echinids as the dorso- 

 central, mentioning at the same time its homologies in the 

 Asterids and Ophiurids. Fewkes f, who had previously 

 confounded dorsocentral and centro-dorsal, wrote a short time 

 later in tlie same terms. But all our efforts to obtain a greater 

 precision of nomenclature seem to have been in vain, for even 

 such a well-informed writer as the late Professor Neumayr | 

 alluded in 1888 to "die centrodorsale Platte bei Salenien." 

 Unaware, too, that the presence of independent under-basals in 

 the AntedonAarva had been announced by Bury § in 1887, he 

 concluded tliat they are represented by the " centrale Platte," 

 by which he meant the enlarged top stem-joint or centro- 

 dorsal. But as he also recognized the fact that these under- 

 basals are well developed in Marsupites and enclose " eine 

 grosse centrodorsale Tafel," he was driven to the following 

 conclusions || : — " Es scheint demnach, als ob die centro- 

 dorsale Platte dev ausgewachsenen Crinoiden durchaus niclit 

 immer dieselbe morphologische Bedeutung hatte, und auch 

 durchaus nicht nothwendig immer dem gleichnamigen Theile 

 der Antedon-\j?i.x\e. entsprache." But is it so certain that the 

 central plate in the calyx of Marswpites should be called a 

 centro-dorsal at all, i. e. that it is an enlarged top stem-joint ? 

 Twelve years ago I gave reasons for believing it to be a 

 primitively imperforate plate homologous with the dorso- 

 central of ScJcnia, and not a top stem-joint with its central 

 canal obscured by a secondary calcareous deposit^. My 

 arguments have never been refuted ; but palaeontologists have 

 nevertheless continued to speak of the centro-dorsal of Mar- 



• " On some Points in the Morphology and Classification of the 

 Saleuiidse, Agassiz," Ann. & Mag. Nat. Hist. 1887, ser. 5, vol. xix. pp. 119, 

 121. 



t Bull. Mus. Comp. Zoul. 1888, vol. xvii. p. 38. 



i ' Die Stamnie des Thierreichs,' >yien, 1889, Bd. i. p. 493. 



§ " The Early Stages in the Development of Antedon rosacea," Report 

 of the Fifty-seventh Meeting of the British Association, held at Man- 

 chester,_ 1887: London, 1888, p. 735. Also Proc. Roy. Soc. 1887-88, 

 vol. xliii. p. 299. 



I| Op. cit. p. 493. 



% Quart. .Tourn. Micr. Sci. 1878, vol. xviii. pp. 380, 381. 



