372 THE VOYAGE OF H.M.S. CHALLENGER. 
resembling the Fhodocrinites in having five large plates separating the radials, 
Thaumatocrinus differs from them and from most Palzocrinoids in the absence of any 
- higher series of calicular interradial plates resting upon the first series which separate 
the radials. 
Except on the anal side the primary,interradial plates of Thawmatocrinus end simply in 
a free rounded edge at the margin of the disk (Pl. LVI. figs. 1-3, 5), which is doubtless due 
to the simplicity of the arms; for these become free almost at once, and are not connected 
laterally by much perisome in which higher orders of radials could be supported. But in 
the presence of the anal appendage on the azygous interradial (Pl. LVI. figs. 2, 4, 5) 
Thaumatocrinus bears a remarkable resemblance to Reteocrinus as understood by 
Wachsmuth and Springer, and to the Xenocrinus of 8. A. Miller; while the appendage 
has an even closer resemblance to the so called “anal series” of Onychocrinus and 
Taxocrinus, the lowest plate of which rests, not on a basal, but on the upper angles of the 
two first radials. 
There can, I think, be no reasonable doubt that the anal appendage of Thawmato- 
erinus, although free laterally, is homologous with the vertical series of plates in the anal 
interradius of Reteocrinus and Xenocrinus, Onychocrinus and Taxocrinus. But owing 
to the small size of Thawmatocrinus and the simplicity of its rays the anal appendage is 
free ; whereas in the Palzeocrinoids it is united to the more or less branching rays by the 
general series of minute irregular plates which occupy the anal interradius and pass 
gradually upwards into those of the so called vault. 
It is difficult to consider the existence of interradials and of the anal appendage of 
Thaumatocrinus as instances of atavism, for no known Neocrinoid presents any similar ” 
characters, and it is a long way back from a recent Comatula to a Paleozoic Crinoid. 
The reappearance of these characters in such a specialised type as a Comatula is conse- 
quently not a little surprising. Associated with them we find the distinctly embryonic 
characters of persistent basal and oral plates, the latter occurring in no other Comatula, 
together with the simplicity of the undivided arms. 
Thaumatocrinus renovatus, P. H. Carpenter, 1883 (Pl. LVI. figs. 1-5). 
Description of an Individual.—The total width of the calyx across the disk is barely 
2mm.; and the height of the centro-dorsal and radials together is about the same. 
The former (Pl. LVI. figs. 1-4) is rounded below, with its central canal completely 
closed up, so that it must have been detached for some little time from the remainder of 
the stem. The bases of half a dozen cirri are attached to it, and there are pits for the 
reception of two or three more. In the largest stump which is preserved (Pl. LVI. 
figs. 1, 3) the first two joints are quite short, as is usually the case in all cirri; but the 
third reaches a length of 1°5 mm., so that the cirri must have been very like those of 
