87 
tlie anal plate, liis second costal, is represented as hexagonal; in the 
description it is said to be “ obscurely hexagonal,” but as previously stated 
the true outline is pentagonal. On the other hand, the late Prof, de 
Koninck represented^ the outline of both these plates correctly. 
Messrs. M'Coy, De Koninck, and Pattc described Tribrackiocrinus 
as possessing three arms only, and the two last named authors believed 
in the presence of inter-radial plates. Sir P. M‘Coy says — “ The arm- 
bearing plates or scaj)ula3, which are so generally five in the other 
genera, are only three in the present animal, forming a strong peculiarity, 
which it shares only with the genus Triacrinus of Count Munster.”'^ 
Professor de Koninck, sj)eaking of his “premieres pieces radiates,” remarks — 
“ Elies ne sont qu’au nombre de trois, cc qui constitue une veritable 
anomalie dans la structure generate des Crino'ides.”^ It naturally follows 
that, if Trihrachiocrbms possessed only three arms, we should expect to find 
only three radials bearing brachial plates for their support. On the other 
hand, according to the w*eighty 02 )inion of Messrs. 'Wachsmuth and Springer,^ 
“ in three of the radials, the articulating faces form a straight horizontal line, 
and only these plates are ojiposed by regular brachials, the two otlun’s (those 
of the antero-lateral rays) being angular and higher at their distal ends. The 
general outline of the two last mentioned plates indicates that they are 
compound plates, each representing a radial and a bifurcating brachial, which 
probably became anchylosed.” Messrs. Wachsmuth and Springer thus differ 
from the other authors named in regarding all the plates of the third cycle, 
except, of course, the anal plates, as radial to the exclusion of any inter-radial. 
At the same time, they suggest the presence of five instead of three arms, one 
attached to each of the radials with horizontal articulating faces, and one each 
to the two high and angular antero-lateral plates. Speaking of the two last- 
named plates, their words are'’ : “ They evidently supported two arms, one at 
each side ; while the three radials, with articulating brachials, apparently bear 
but a single arm like Cronyocrinus simplex, Trautschold.” 
A most careful examination of all available examples of Trihmchio- 
crinus has been made, including the specimen from which the cast was taken, 
and forwarded by Mr. Kattc to Messrs. AYachsmuth and Springer; and, although 
I must admit that there is every a 2 :>pearance of constricted distal ends to these 
* Foss. Pal. Noiiv'. Galles du Sud, 1877, Pt. 3, p. 23. 
Ann. Mag. Nat. Hist., 1847, XX, p. 228. 
5 Foss. Pal. Nouv.-Galles du Sud, Pt. 3, 1877, p. 162. 
^ Kevision of the Palfeocrinoidea, 1886, Pt. Ill (2), p. 250 (174). 
® Revision of the Paleeocrinoidea, 1886, Pt. Ill, p. 250 (174). 
11a 64—92 E 
