Sad iad 
REPORT ON THE. CRINOIDEA. 371 
of the larval stem, I have preferred to describe it in the same part of the Crinoid Report 
as the Stalked Crinoids. For it is only among certain of the Paleocrinoidea that 
we meet with characters which are at all like the more striking pecularities of. 
Thaumatocrinus. 
There can, I think, be no doubt that the large and comparatively dense oral plates are 
not in a state of resorption as they are in other Comatuls of the same size ; for they 
have all the appearance of being permanent structures. Thaumatocrinus is therefore the 
only Comatula yet known in which the oral plates of the larva persist through life as in 
Hyocrinus and Rhizocrinus. 
Another striking peculiarity is presented by the closed ring of relatively large basals 
which have remained in their primitive position upon the exterior of the calyx and have 
not undergone transformation into a rosette, as is the case in most other Comatule.. The 
only other recent type in which the basals remain visible on the exterior of the calyx is 
the curious genus Atelecrinus ; 1 and here they are very small in proportion to the radials. 
This is probably also the case in the Cretaceous species which is mentioned by Schliiter * 
as provided with a closed basal ring. 
Both the persistence of the basals and the considerable development of the orals are 
characters which, either singly or combined, would cause the type to be regarded as one 
of no little interest; but they are altogether cast into the shade by the other peculiarities 
of the calyx, viz., the complete separation of the radials by relatively large interradial 
plates and the presence of the anal appendage. It has been shown elsewhere ® that in 
the separation of its radials laterally Thawmatocrinus is permanently in the condition of 
‘4 Crinoid larva at a very early period of Pentacrinoid life, and that this condition is 
characteristic of certain Paleeocrinoids belonging to the family Rhodocrinide. Some genera, 
such as the Lower Silurian Reteocrinus and Xenocrinus, have the radials separated by 
what Messrs. Wachsmuth and Springer * describe as an “interradial series resting directly 
upon the basals, consisting of a very large number of minute pieces of irregular form, and 
without definite arrangement.” A similar development of small irregular plates between 
the rays occur in many Neocrinoids, both stalked and free, but the interradial series always 
commence at the level of the second or third radials, and are completely separated from 
the basals by the ring of united first radials. This is well seen in Pentacrinus asterius 
(Pl. XIIL fig. 1) and in the fossil Extracrinus. 
In other genera of the Rhodocrinidie such as Rhodocrinus itself, Thylacocrinus, and 
others forming the section Rhodocrinites, the first radials are separated not by small and 
irregular plates as in Reteocrinus, but by large plates, one resting on a basal in each 
interradius; and this is the condition of 7 haumatocrinus (Pl. LVI. figs. 1-4). While 
1 Bull. Mus. Comp. Zobl., vol. ix., No. 4, 1881, p. 16, pl. i. figs. 1-7. 
2 Zeitschr. d. deutsch. geol. Gesellsch., Jahrg. 1878, p. 66. 
3 Phil. Trans., 1883, part iii. pp. 923-926 ; and ante, pp. 39, 40. 4 Revision, part ii. p. 192. 
