152 THE VOYAGE OF H.M.S. CHALLENGER. 
None of the Neocrinoids, however, have permanently imperforate radials as so many 
Palzeocrinoids have, the latter group remaining in anembryonic condition as stated already. 
In by far the larger number of Neocrinoids which have divided rays, the axillary is 
the third of the primary radials. The only exceptions are Metacrinus and Plicatocrinus. 
In the former genus (Pl. XXXIX. fig. 1; Pl. XLVI.) the first and the axillary radials 
are primitively separated by from three to six joints, some of which afterwards become 
united by syzygy; while in Plicatocrinus there appear to be only two radials altogether, 
the first and the axillary. Zittel’ describes three, it is true, or rather two radials and 
an axillary brachial; but he speaks of the “innig verschmolzenen Plittchen der unteren 
Zone’ as quite small, and I am strongly inclined to suspect that they represent basals 
rather than first radials. For what he calls the second radials seem to me to be the 
first or calyx radials. They are the large trapezoidal plates forming the greater part of 
the calyx, and united to the lower series by suture ; and such a mode of union of the two 
lower radials occurs in no other Neocrinoid except G'uettardicrinus. 
The position of the axillary joint in those Paleocrinoids which have divided rays is 
by no means so fixed as in the younger types, for the first radials themselves may be 
axilliary as in Allagecrinus ; while in Poteriocrinus radiatus the axillary is the sixth joint 
beyond the first radial, as in some species of Metacrinus (Pls. XLIV., XLVI, XLVIL-L.); 
and in other genera its position may be anywhere between these two extremes. This is 
in fact the only important character which distinguishes the Paleeozoic Erisoerinus, 
Philocrinus, and Stemmatocrinus from the well known Triassic genus Hncrinus. 
Erisocrinus has distinct under-basals like those of Encrinus, though relatively larger ; 
but in Stemmatocrinus, according to Wachsmuth and Springer,’ these plates are 
represented by a flat disk, which is undivided, regularly pentagonal, and extends 
considerably beyond the periphery of the column. Trautschold? appears to take the same 
view of Stemmatocrinus. Tempting as it may be, owing to the way in which it would 
increase the resemblance between these types and Encrinus, I feel somewhat loth to accept 
it. For the plate in question appears to me to be much more truly represented by 
the central pentagonal piece on which the basals of Cupressocrinus rest; this is larger 
than the stem-joints beneath it, and is obviously what Schultze‘ calls it, viz., “Hine 
fiinfseitige, aus der Erweiterung des obersten Siiulengliedes gebildete Platte.” Unfortun- 
ately we are not acquainted with the mode of development of the under-basals, as they 
oceur in no recent Crinoid; but the analogy of the development of the other calyx- 
plates indicates that they are primitively five separate plates, like their homologues in the 
apical system of Ophiurids and Starfishes ; and a theory which would homologise them 
with a plate that first appears as a simple ring, seems to me to run counter to all true 
1 Ueber Plicatocrinus, Joe. cit., pp. 107, 108. 2 Revision, part i. p. 141. 
3 Einige Crinoideen und andere Thierreste des jiingeren Bergkalks im Gouvernment Moskau, Bull. Soc. Imp. des 
Nut. Moscou, 1867, p. 28. 
4 Op. cit., p. 15, Taf. ii. figs. 1 a, 6 a. 
i ee 
