Anatomical Nomenclature of Echinoderms. 15 
Under these circumstances it has been agreed between 
Messrs. Wacbsmuth and Springer and myself to describe all 
Crinoids as possessing but one radial in each ray ; and it can 
then be referred to without the prefix “ primary/’ which has 
hitherto been necessary in comparing this plate with what we 
believe to be its homologue in Urchins and Stellerids. All 
plates beyond this which lie in a radial direction are arm- 
plates or brachials, those beyond the first axillary being called 
for descriptive purposes distichals, palmars, and postpalmars, 
as explained above. But it now becomes necessary to find 
some convenient descriptive name for the plates between the 
radial primaries and the distichals, which have hitherto been 
known as the outer radials in the Neocrinoids generally. It 
is difficult to find a rational one which shall have the merit of 
brevity, and w T e have therefore decided to revert to the purely 
empirical term “ costals.” This was invariably employed by 
J. S. Miller * to denote the second radials, where he did not 
call them arm-plates, as will appear from the subjoined table 
(p- 16). 
Miller’s terminology was not strictly logical, and one can 
hardly expect that it should have been so ; but at any rate it 
served as a foundation for much valuable work, and I think 
it only right to employ one of his terms when this is possible 
without straining analogy too far. The plates which Miller 
sometimes called first costals and sometimes scapulas are far 
better described by Muller’s name “ radials ; ” but I think 
that we may fairly employ the names first and second costals 
for the second and third radials of Muller, now that it is 
agreed by every one that they are morphologically arm-joints. 
In seven of the eight generic descriptions in which Miller 
used the term costals at all it was applied to plates in the direc- 
tion of the rays, and in one genus only ( Gyathocrinus ) did he 
definitely give this name to interradial plates, and then in but 
three of its four species. It is somewhat unfortunate therefore 
that in his classical memoir on the Echinoidea Loven should 
have proposed to specialize this name as denoting the primary 
interradial plates of the Echinoderm apical system, i. e . the 
genitals of Urchins and the basals of Crinoids j\ I pointed 
this out in 1878 J, and Lovdn, while admitting Miller’s incon- 
sistency, replied that “ It has always been considered allow- 
able to suggest the use in a strict sense of a term elsewhere 
vaguely applied ” §. This is of course quite true ; but the 
* ‘ A Natural History of the Crinoidea/ Bristol, 1821. 
t Op. cit . p. 73. 
X Quart. Journ. Micr. Sci. 1878, vol. xviii. p. 363. 
§ “ On Pourtalesia , a Genus of Echinoidea,” Kongl. Svenska Vetens- 
kaps-Akademiens Handlingar, 1883, Bd. xix. no. 7, p. 64. 
