Structure o/Crotalocrinus. 403 



the small covering plates of Crofalocrinus rugosus are the 

 representatives in a smaller Crinoid of the " Iar2;e rigid plates " 

 shown in tigs, 6 and 7, not on pi. 6, as Wachsrauth and 

 Springer again quote it, but on tab. viii. of Angelin's ' Icono- 

 graphia ; ' while I shall also continue to believe, until the 

 contrary is demonstrated, that the central plate and proximals 

 are among the irregular pieces occupying the oral pole in the 

 originals of these two figures, and not beneath them, although 

 Wachsmuth and Springer "know" this latter fact "to be true." 



The question of the presence or (as I believe) the absence 

 of a flexible vault composed of calyx-interradials above the 

 summit-plates and covering pieces of Crotalocriaus is one of 

 extreme importance in the morphology of the PaljBocrinoidea, 

 for Wachsmuth and Springer's knowledge of its existence is 

 employed in many cases as an argument in favour of their 

 views respecting the great development of the ahactinal 

 interradial plates of Pala^ocrinoids above the ac/5»ia/ side, and 

 also for the purposes of classification. 



We are told, for example, respecting Crotalocrinus and 

 Enallocrtnus * : — " The summit-plates in both genera are sub- 

 tegminal, being covered completely by interradials, and the 

 same was probably the case in the allied Ichthyocrinidaj, at 

 least in their earlier forms. Reteocrinus and Xenocrinus were 

 evidently in a similar condition, but it is not known whether 

 they had summit-plates beneath the interradials or not." As 

 I have before remarked f, the word " evidently " is here used 

 by the authors as a short way of expressing " in our opinion." 

 A little lower down the same page the supposed condition of 

 Reteocrinus is also employed to enforce their argument : — 



" It has been proved from palseontological evidence that in the 

 earlier genera the interradials are more extravagantly developed 

 than in later ones. In Crotalocrinus and Reteocrinus the interradials 

 cover the entire ventral surface ; in Glyptocrirws and Olyptaster 

 they recede gradually toward the periphery, and the central space 

 is filled by large proximals, and often by radial dome-plates. Con- 

 sidering these facts, is it safe to assert that in Allagecrinus and 

 Hcqjlocrimis, which are regarded as larval forms, interradials are 

 entirely absent, and that all ventral plates are actinal ? Is it not 

 more reasonable to imagine that in these low forms the ventral side 

 was covered by the one plate in a similar manner as in Crotalo- 

 crinus, Reteocrinus, and GJyptocrinus by the whole collection of 

 plates ? In the Neocrinoidea, from the larva to the adult, all 

 ventral plates are actinal, but in all Palaeozoic Crinoids, and we 

 may say in all Palaeozoic Pelmatozoa, the whole, or at least the 



* ' Revision,' part iii. p. 57. 



t Ann. & Mag. Nat. Hist. March 1886, ser. 5, vol. xvii. p. 288. 



