Anatomical Nomenclature of Echinoderms. 11 



had ciuleavourcd to koej) 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 liim unfairly *. The combination does occur, how- 

 ever, but in the singuhir number, on p. KiO of his paj)er, as I 

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

 gotten his use of it. 



He also attempts to justify himself by stating that " Sladen 

 in considering certain starfishes uses iuterradial for basal, and 

 to explain what he means by interradials uses the following 

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

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

 not quoted Sladen correctly. lie does not seem to have 

 appreciated the fact that the whole ])oint of my criticism 

 related to his use of the words iuterradial 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 Sladen 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 appears to me that lie 

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

 subject which already bristles with ditiiculties. 



4. The Radial Plates. 



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

 situated in the direction of the rays between the basals and 

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

 arms. His terminology was employed by Eoemer, Beyrich, 

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

 modified it very considerably J. He adopted the principle 

 that the lowest articular facet indicates the boundary-line 

 between radials and brachials. In his diagrams of Taxo- 

 crinuSy ZeucrinuSy 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 " Monograpbie der Echinodermen des Eitler Kalkes," Denkscbr. k. 

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



