Anatomical Nomenclature of Echinodcrma. 15 



Under these civcumst.inceg it has been agreed between 

 Messrs. Wachsmuth 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 ]>latc witli what we 

 believe to be its homologue in Urchins and Stellcrids. All 

 plates beyond tliis which lie in a radial direction arc arm- 

 plates or brachials, those beyond the first axillary being called 

 for descriptive pur[)Oses distichals, palmars, and postpalmars, 

 as explained above. But it now becomes necessary to find 

 some convenient descriptive name for the ])lates between the 

 radial primaries and the distichals, which have hitherto been 

 known as the outer radials in the Neocrinoids generally. It 

 is difhcult to find a rational one which shall have the merit of 

 brevity, and we have therefore decided to revert to the purely 

 empirical term " costals." This was invariably employed by 

 ,1. S. Miller* to denote the second radials, where he did not 

 call them arm-plates, as will appear from the subjoined table 

 (p. IG). 



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 scapulae are far 

 better described by Miiller's name " radials ; " but I think 

 that we may fairly employ the names first and second costals 

 for the second and third radials of Miiller, 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 {Cijathocrinus) 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 Lovdn should 

 Lave 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 f. I pointed 

 this out in 1878 |, and Loven, 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. Joum. Micr. Sci. 1878, toI. xviii. p. 3G3, 

 § '' On Pourtalesia, a Genus of Echinoidea," Jvongl. Sveuska Vetens- 

 kaps-Akademieus Ilandliugar, 1883, Bd. xix. no. 7, p. 64. 



