Structure <?/ Crotalocrlnus. 399 



and several rows of covering pieces, without the intervention of 

 either anambulacral or interradial pieces. It would be difficult with 

 the utmost stretch of our imagination to recognize in the former 

 figures either proximals or central piece, which, as admitted by 

 Carpenter, are present in all these Crinoids, and we think there can 

 be little doubt that the two sets of figures represent diff"erent parts 

 of the animal, the one the disk, the other the vault, and that the 

 one covered the other. A similar opinion was evidently entertained 

 by Zittel (Handb. d. Paloeont., i. p. 357), who stated that Crotalo- 

 crinus possessed five ' grosse Oralplatten, bald unter der Decke, 

 bald ausserlich sichtbar.' According to our interpretation the calyx 

 of the Crotalocrinidee extends ventrally to the oral pole, and the 

 ambulacra, central piece, and proximals are subtegminal, covered by 

 interradial plates, which extend out to the lower rows of covering 

 plates and side pieces (Icon. Crin. Suec, pi. 7, fig. 6, and pi. 25, 

 fig. 15). A similar condition probably prevailed in the Ichthyo- 

 crinidoe, with which the Crotalocrinidse have close affinities." 



Of Angelin's four figures first referred to by Wachsmuth 

 and Springer in the above paragraph, the first and last (tab. vii. 

 fig. 3 a, and tab. xxv. fig. 2) represent Enallocn'nus scriptusj 

 and the other two (tab. viii. figs. 6 & 7) Crotalocrinus pul- 

 clier. Fig. 3 a on tab. xvii. represents the vault of Crotalo- 

 crinus rugosus, and the central plate with the four anterior 

 proximals is very distinct, as admitted by Wachsmuth and 

 Springer. But when they state that " there is no central piece, 

 nor proximals, nor traces of ambulacra " in the figures of 

 Crotalocrinus ]3ulclier and Enallocrinus scriptus they appear 

 to me to be seriously in error. 



No one knows better than the American authors that while 

 the summit-plates are clear and well defined in some species 

 and genera, there are other closely allied forms in which these 

 plates are almost or entirely undistinguishable among the 

 large number of plates to be found in the vault. I will now 

 only mention one instance in illustration of this statement^ viz. 

 Cyathocrinus iowensis and C. multibrachiatus^ both of which 

 are figured by Wachsmuth and Springer *, the former with 

 and the latter without very distinct summit-plates ; and I might 

 name any number of similar cases in the arrangement of the 

 plates of the Echinoderm apical system, especially among 

 the Ophiurids. 



But the argument used by Wachsmuth and Springer is of 

 this kind : — I. The vault of Crotalocrinus j)ulclier and of 

 Enallocrinus scriptus is composed of irregularly disposed 

 plates, none of which are specially distinguishable as the 

 summit-plates. 2. The vault of Crotalocrinus rugosus^ how- 



* ' Revision,' part iii. p. 65, pi. iv. fig. 6, and pi. v. fig. 7. 



