No. 1613. THE CRINOID GENUS EUDIOCRINUS—CLARK. 275 
and costal axillaries and first brachials, eawcept that the transverse 
ridge separating the dorsal-ligament fossa from the interarticular 
ligament fosse is strongly diagonal, and the other elements making 
up the sculpture of the joint face are correspondingly misplaced. 
The diagonal position of the transverse ridges al- 
ways alternates on succeeding joints, the external posi- 
tion of these ridges being marked by a series of more 
or less prominent alternating tubercles along the arm, 
the first of these tubercles being always exterior, in 
reference to the last axillary. 
It will now be seen that, judging from the types 
of articulations, the two costals are merely repetitions 
of the first two brachials, interpolated between them 
and the radials; in the cases where the arms divide 
Rahs Fie. 4.—DORSAL 
more than once, the distichals, palmars, postpalmars, — yrew or rue Ra- 
etc., are really additional repetitions of the first two P41; COsTALS, 
. ‘ AND LOWER BRA- 
brachials, for we always find the first two brachials — curarsor THav- 
of a free arm the same, no matter how many division Sah ey eee 
series may intervene between them and the radials; in © srrvucturmoran 
the cases where the division series are 4 (3+ 4), Ree fee ey 
there is merely a double instead of a single repetition 
of the first two brachials, for the first two joints are here united by 
synarthry into one pair, the last two united by syzygy into another 
pair; but the two pairs are united by an articulation resembling 
that found between the radials and first costals, and between all 
| aXxillaries and the succeeding joints. 
Additional evidence that this is really the case is found 
in the cases where, as in Perometra diomedew, there: is 
an extravagantly elongated tubercle on the articulation 
between the first two brachials; this is repeated between 
the costals; or, as in Tropiometra, where the first two 
brachials are greatly enlarged; the costals are very large 
also; or in various species of Charitometra and Thalas- 
sometra, where the first two brachials are highly orna- 
Fic.5.—_bor. mented; the costals and division series are always simi- 
sat vi=w larly ornamented. 
OF RADIALS 
AND LOWER In Decametrocrinus and in the Hudiocrinus japonicus 
oe ene COLE (fig. 5) we find the articulation between the first 
merrocrr. two post-radial joints to be exactly like that between the 
pegeeiebe first two brachials, or the costals, in any ten-armed coma- 
. tulid, 1. e., a synarthry; but the articulation between the 
second and third and all succeeding joints corresponds to the 
articulations between the second and third and all succeeding 
brachials in the free arms of ordinary comatulids. Thus, then, the 
arms of these forms are strictly homologous to the arms of other 
comatulids beyond the last awillary,; it is as if the arm of a Heliometra 
