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 u adaxial interradials,” and implies that I have 
criticised him unfairly *. The combination does occur, how- 
ever, but in the singular number, on p. 1B0 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 u Sladen 
in considering certain starfishes uses interradial for basal, and 
to explain what he means by interradials uses the following 
combination: — ‘interradials (i. e. basals).’ ” I am sorry to 
say, however, that Fewkes is again in error, and that he has 
not quoted Sladen 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 (i. e . basal) plate 99 1* 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 Orinoidea since the time of Muller, 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 u ad- 
axial interradial 99 of an Ophiurid it appears 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 “Radialia” was given by Muller 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 Roemer, Beyrich, 
de Koninck, and other writers till the time of Schultze, who 
modified it very considerably f . He adopted the principle 
that the lowest articular facet indicates the boundary-line 
between radials and brachials. In his diagrams of Taxo - 
crinus , Zeacrinus , Rhodocrinus ) and Actinocrinus the first 
* Bull. Mus. Comp. Zool. 1888, vol. xvii. p. 45. 
t Quart. Journ. Micr. Sci. 1884, vol. xxiv. p. 33. 
t " Monographie der Echinodermen des Eider Kalkes,” Denkschr. k. 
Akad. Wissensch. Wien, 1867, Bd. xxvi. Abth. 2, p. 117. 
