TERMINOLOGY. 33 
bearing ones, constitute the nodal joints, and those interposed between them 
the énfernodal joints. The term dorsocentral is used for the enlarged terminal 
joint of the stem, by which the young Crinoid is attached to other objects ; 
and centrodorsal for the modified, cirrus-bearing top joint of the Comatule, 
as well as for the plate within the infrabasal ring of the Marsupitide. The 
longitudinal canal, passing through the centre of the stem, is the arial canal. 
In speaking of the form of the stem, allusion is made to the transverse 
section. 
The crown consists of calyx and arms; the former encloses the visceral 
cavity; the latter constitute the free appendages, passing off from, and con- 
necting with the calyx. 
The calyx is composed of the dorsal cup, and the ventral disk or tegmen, the 
arm regions forming the line of demarkation between them. The dorsal 
cup conforms in a general way to the apical or abactinal system of the 
Echinoderms, the ventral disk to the oral or actinal system. 
The dorsal cup, in its simpler form, is constructed of basals, tufrabasals, 
when present, and radials ; to which must be added the anal plates, which, 
however, are not always represented. In the more complex form it includes 
also some of the lower brachials, which have been incorporated into the 
walls, either by lateral union among themselves, or by means of interradial 
and interaxillary plates; the last mentioned plates, in that case, also form- 
ing part of the cup. All Crinoids belonging to the simpler form are dis- 
tinguished as Crinoidea Inadunata ; those of complex form, when the calyx is 
rigid, as Crinoidea Camerata, but when flexible, as Crinoidea Articulata. 
The dase, or part next to the column, may be composed of one or two 
rings of plates, which are distinguished as dasa/s and infrabasals. The basals 
adjoin the radials and alternate with them, being interradial in position. 
The infrabasals, when present, are radially disposed below the basals.  Cri- 
noids in which the base consists of a single ring of plates are called mono- 
cyclic ; those with two rings, dicyche. 
The radials consist of the first plate of each ray, and all plates beyond 
this in radial succession are brachials ; fixed brachials so far as they take 
part in the calyx, free brachials or am plates when they do not. In some of 
the earlier Crinoids one or more of the radials are bisected transversely, in 
which case the two parts are distinguished as suwper-radials and infer-radials. 
The arms may be simple or branching. When the divisions are of equal 
size, and rise to the same general height, they are regarded as parts of the 
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