Terms in Crinoid Morphology. ~ ee) 
tology of New York,’ vol. i. (1848). It seems to me there= 
fore that the use of the term “ costals’’ in the.sense now pro= 
posed cannot be justified, and I regret that I ever agreed to 
use it. 
The objective difficulties in the way of the proposed termi- 
nology are due to the more correct views that are now held 
with regard to the homologies of pinnules. As was fully 
explained in the section on the Arms in “ British Fossil 
Crinoids,” Part IL. (p. 374), pimnules are nothing more than 
armlets that have become small, ceased to branch, and are 
regularly placed on alternate sides of successive ossicles. An 
armlet itself is merely one branch of a dichotomous arm 
reduced in size. Consequently, from a morphological stand- 
point, a pinnule, however small, is the homologue of a whole 
dichotom (as we may conveniently call such a branch), while 
the ossicle that supports a pinnule is simply an axillary, and 
this without going beyond the strict conception of that term 
as recently laid down by Carpenter (op. cit. p. 19). 
If now we turn to such a genus as Botryocrinus, and com- 
pare two of its species, such as B. ramosus and B. decadac- 
tylus *, and if we name the successive orders of brachials after 
the methods hitherto followed, we shall come to these con- 
clusions—that 
in B. ramosus in B. decadactylus 
the costals are homologous with the costals ; 
the distichals » with the first two distichals ; 
the distichal axillary ,, with the second distichal ; 
the palmars » With the third distichal and the first pinnule, 
or, if this pinnule is branched, with the 
Z proximal portion thereof ; ; 
the first postpalmars ,, with the fourth distichal, the second pinnule, 
and the branches of the first pinnule if it 
: be branched ; 
the second postpalmars ,, with the fifth distichal and third pinnule; _ 
and so on. Which conclusions appear a sufficient reductio ad 
absurdum of our present methods. ‘Those methods were only 
legitimate so long as pinnules were considered to be struc- 
tures distinct from arm-branches and preseut or not according 
to some unrecognized or, at the best, empirical system. 
From the foregoing review of the circumstances it appears 
that a terminology is required that shall fulfil the following 
conditions. Homologous parts must receive the same name. 
Parts serially homologous must receive names of a similar 
nature. When specialization and differentiation have taken 
. * Brit, Foss, Crin., V., Ann. & Mag. Nat. Hist. ser. 6, vol. vii. pp. 394 
and 398. on til od 
