Anatomical Nomenclature of Echinoderms. 11 



had endeavoured to keep distinct as denoting different struc- 

 tures, he denies that he has anywhere made use of the combi- 

 nation " adaxial interradials," and implies that I have 

 criticised him unfairly *. The combination does occur, how- 

 ever, but in the singular number, on p. 1/iO of his paper, as I 

 have quoted above, though he seems to have entirely for- 

 gotten his use of it. 



He also attempts to justify himself by stating that " Sladen 

 in considering certain starfishes uses interradial for basal, and 

 to explain what he means by interradials uses the following 

 combination: — 'interradials (/. e. basals).'" I am sorry to 

 say, however, that Fewkes is again in error, and that he has 

 not quoted iSladen correctly. He does not seem to have 

 appreciated the fact that the whole point of my criticism 

 related to his use of the words interradial and basal as sub- 

 stantives with identical meanings, and he quotes Sladen as 

 having done so. Sladen's expression, however, is " inter- 

 radial («'. e. basal) plate " f- Of course the basal plates are 

 interradial, i. e. situated between the rays ; but they are not 

 interradials as this term has been understood by students of 

 the Crinoidea since the time of Miiller, and Sladeu did not 

 call them so, though Fewkes did. 



The question is not a very important one ; but I cannot 

 help thinking it desirable that terms which have a very defi- 

 nite meaning in the anatomy of one type should only be 

 applied to homologous parts in descriptions of other types ; 

 and when Fewkes writes about the " abaxial basal " or " ad- 

 axial interradial " of an Ophiurid it a{)pears to me that he 

 is placing needless obstacles in the way of the students of a 

 subject which already bristles with difficulties. 



4. The Radial Plates. 



The name "Eadialia^' was given by Miiller to all the plates 

 situated in the direction of tlie rays between the basals and 

 the first axillary (inclusive) of a Crinoid with more than five 

 arms. His terminology was employed by Roemer, Beyrich, 

 de Koninck, and other writers till the time of Schultze, who 

 modified it very considerably \. He adopted the principle 

 that the lowest articular facet indicates the boundary-line 

 between radials and brachials. In his diagrams of Taxo- 

 crinus, ZeacrinuSf Rhodocrinus^ and Actinocrinus the first 



» Bull. Mu3. Comp. Zool. 1888, vol. xvii. p. 45. 

 t Quart. Journ. Micr. Sci. 1884, vol. xxiv. p. 33. 

 X " Mouographie der Echinodermen des Eitler Kalkes," Deuksclu-. k. 

 Akad. Wissensch. Wien, 1867, Bd. xxvi. Abth. 2, p. 117. 



