REPORT ON THE CRINOIDEA. 371 



of the larval stem, I have preferred to describe it in the same part of the Criuoid Report 

 as the Stalked Crinoids. For it is only among certain of the Palseocrinoidea 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 Comatulse of the same size ; for they 

 have all the appearance of being permanent structures. Thaumatocriiius 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 Comatulse. The 

 only other recent type in which the basals remain visible on the exterior of the calyx is 

 the curious genus Atelecrinus ; ^ and here they are very small in proportion to the ra dials. 

 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 sho'UTi elsewhere ^ that in 

 the separation of its radials laterally Tliaumatocrimis is permanently in the condition of 

 a Crinoid larva at a very early period of Pentacrinoid life, and that this condition is 

 characteristic of certain Palseocrinoids belonging to the family Rhodocrinidas. 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 hy the ring of united first radials. This is well seen in Pentacrinus asterins 

 (PL XIIL fig. 1) and in the fossU Extixicrimis. 



In other genera of the Rhodocrinidse such as Rhodocrmus itself, Tliylacocnnus, 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 Thaumatocrinus (PI. LVI. figs. 1—1). AMide 



1 Bull. Mus. Comp. Zoiil, vol. ix., No. 4, 1881, p. 16, pi. i. fig.^. 1-7. 



2 Zeitschr. d. deutsch. geol. Gesellsch., Jalirg. 1878, p. 66. 



3 Phil. Trans., 1883, part iii. pp. 923-925 ; and ante, pp. 39, 40. * Revision, part ii. p. 192. 



