14 Dr. P. II. Carpenter on (he 



begin immediately beyond tlie primary radials. But if the 

 lower arm-plates form a part of the dorsal cup, those up to 

 and including the first axillary are called radials, wliile their 

 successors up to the next axillary retain their Miillerian 

 name, distichals, those beyond them again being called disti- 

 chals of the second order. 



Ever since I began to write on the Crinoids, now some 

 thirteen years ago, I have used this term distichals to denote 

 the plates between the first and the second axillary (inclusive) 

 of Crinoids with more than ten arms, whether these be free 

 or united by interradial plates ; while the plates up to and 

 including the third axillary, should such occur, have been 

 called palmars. This method has been adopted by other 

 writers on recent Crinoidea, and has been found to work well 

 in practice, as it is obviously much shorter to say " distichals " 

 than " radials of the second order" or " brachials of the first 

 order." " Palmars " in like manner is a preferable term to 

 " radials of the third order," and the succeeding axillaries, 

 when present, may be conveniently called first, second, third 

 postpalmars, &c. For purely descriptive purposes it is not 

 often necessary, either for recent or for fossil Crinoids, to refer 

 to more than three axillaries above the radials, viz. distichal, 

 palmar, and postpalmar ; and Messrs. Wachsmuth and 

 Springer have agreed to use these terms for the future in 

 their descriptions of Palajocrinoids. 



It has also seemed desirable to arrive at some sort of agree- 

 ment as to the nomenclature to be adopted for the plates 

 between the basals and the first bifurcation in Crinoids with 

 ten or more arms. JMiiller called them all radials in every 

 Crinoid, and the same course has been adopted by de Loriol 

 and myself; while other authors have endeavoured to distin- 

 guish between the first plate and its successors according to 

 their ideas respecting the position of the first articular surface 

 or the extent to which the outer plates are included in the 

 dorsal cup. But it will be evident from what has been said 

 above that neither of these criteria is a satisfactory one, and 

 that there is consequently a great want of unanimity between 

 difterent authors, and even in different parts of the same work, 

 so that the result cannot but be most perplexing to the 

 student. All the leading writers are agreed, however, that 

 the arms really commence with the first plates above the 

 primary radials, and not above the first axillaries, {. e. that 

 the plates which are sometimes called the outer radials, situa- 

 ted between the primary radials and the distichals, are really 

 arm-plates; while, as Zittel has pointed out, there are develop- 

 mental reasons for considering this to be the case *. 

 * Op. cif. p. 330. 



