14 
Dr. P. H. Carpenter on the 
begin immediately beyond the 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, while their 
successors up to the next axillary retain their Mullerian 
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 u distichals ” 
than cc radials of the second order ” or u brachials of the first 
order.” u Palmars ” in like manner is a preferable term to 
u 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 Palseocrinoids. 
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. Muller 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 w~ant of unanimity between 
different 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, i. 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. cit. p. 339. 
