148 THE VOYAGE OF H.M.S. CHALLENGER. 
types from the group of the Neocrinoids, to which they have been already provisionally 
referred by de Loriol. 
Both have uniserial arms, a symmetrical calyx, and no anal side; while in 
Marsupites, at any rate, the first radials were perforated by canals, and united to the 
second by muscular joints. Interradial plates, however, are well developed in both 
genera, especially in Uintacrinus. But the upper series of so-called interradial and 
interdistichal or interaxillary plates are really parts of the radial system, and correspond 
to the pinnules of free arms, as was pointed out by Meek. At the same time he noted 
their unusual size, and the fact that they are united with each other and with the main 
divisions of the rays for some distance up, so as to constitute a part of the walls of 
the body." 
Schliiter,? to whom Meek’s remarks seem to have been unknown, speaks of this as a 
possibility, but rejects it on account of the absence of a central canal in the supposed 
pinnule-joints, and other less important reasons. I cannot help suspecting, however, 
that the canal will be found, and that the plates in question are really the basal joints of 
the large lower pinnules, He describes how these plates group themselves together in 
double rows, the lowest of which “geht aus von dem zweiten Distichalgliede. Sie 
besteht vielleicht aus 9 Stiicken jederseits. Die folgende Doppelreihe, aus kleineren 
Tiifelchen zusammengesetzt, nimmt ihren Anfang vom fiinften Stiicke iiber dem 
Axillare.” The first pimnule being on the second brachial, the next on the same side 
would be on the fourth; but since the third is a syzygial or double joint, the fourth 
brachial is primitively the fifth above the axillary; while Schliiter’s figures® show that 
the double row of interdistichal pieces which ‘ 
Distichale aus” are really the pinnules on the epizygals of the two third brachials. There 
are many species of recent Crinoids (Pentacrinus, Metacrinus, Actinometra) which have 
large lower pinnules with the basal joints closely fitted together just as in Uintacrinus 
(Pl. XXXVITI.; Pl. XXXIX. fic. 1; Pl. XLII. fig. 2; Pl LIT. fig. 1); so that the 
supposed resemblance in this respect between Uintacrinus and the Palzeocrinoids goes 
for nothing. Apart from these two genera there are no Secondary Crinoids which could 
by any possibility be referred to the Tessellata; and this is still more emphatically the 
case with the Tertiary and recent forms. It is true that the most striking characters of 
the recent Thawmatocrinus (Pl. LVI. figs. 1-4) indicate an affinity to early Paleozoic 
types (ante, pp. 39-46) ; but, considering that Thawmatocrinus is a Comatula, it is 
more than probable that this resemblance is not due to any genetic connection. 
Thus then I regard the Neocrinoids as constituting a group or subclass which is 
distinctly marked off from its Paleozoic predecessors. These became extinct with the 
Paleozoic epoch, like the Blastoids, Cystids, and Paleechinoids. The latter in fact 
‘nehmen ihren Anfang vom vierten 
? 
1 Grinnel, Note on the genus Uintacrinus, Bull. U.S. Geol. and Geog. Survey of the Territories, vol. ii., No. 4, p. 377. 
2 Op. cit., p. 58. 3 Op. cit., Taf. iv. figs. 1, 3. 
