152 THE VOYAGE OF H.M.S. CHALLENGER. 



None of the Neocrinoids, however, have permanently imperforate radials as so many 

 Pateocrinoids have, the latter group remaining in anembryonic condition as stated already. 

 Tn by far the larger number of Neocrinoids which have divided rays, the axillary is 

 the third of the primary radials. The only exceptions are Metacrimis and Plicatocrinus. 

 In the former genus (PI. XXXIX. fig. 1 ; PI. XLVI.) the first and the axillary radials 

 are primitively separated by from three to six joints, some of which afterwards become 

 united by syzygy ; while in Plicatocrinus there appear to be only two radials altogether, 

 the first and the axillary. Zittel ^ describes three, it is true, or rather two radials and 

 an axillary brachial ; but he speaks of the " innig verschmolzenen Plattchen der unteren 

 Zone ' as quite small, and I am strongly inclined to suspect that they represent basals 

 rather than first radials. For what he calls the second radials seem to me to be the 

 first or calyx radials. They are the large trapezoidal plates forming the greater part of 

 the calyx, and rmited to the lower series by suture ; and such a mode of union of the two 

 lower radials occurs in no other Neocrinoid except Guettdrdicrinus. 



The position of the axillary joint in those Palseocrinoids which have divided rays is 

 by no means so fixed as in the younger types, for the first radials themselves may be 

 axilliary as in AUagecrinus ; while in Poteriocrinus radiattis the axillary is the sixth joint 

 beyond the first radial, as in some species of Metacnnus (Pis. XLIV., XLVL, XLVII.-L.) ; 

 and in other genera its position may be anywhere between these two extremes. This is 

 in fact the only important character which distinguishes the Palaeozoic Erisocrinus, 

 Philocrinus, and Stemmatocrinus from the well kuowai Triassic genus .Encrimis. 

 Erisocrinus has distinct under-basals like those of Encrinus, though relatively larger ; 

 but in Stemmatocrinus, according to Wachsmuth and Springer," these plates are 

 represented by a flat disk, which is undivided, regularly pentagonal, and extends 

 considerably beyond the periphery of the column. TrautschokP appears to take the same 

 view of Stemmatocrinus. Tempting as it may be, owing to the way in which it would 

 increase the resemblance between these types and Encrinus, I feel somewhat loth to accept 

 it. For the plate in question appears to me to be much more truly represented by 

 the central pentagonal piece on which the basals of Citjyn'ssocrinus rest ; this is larger 

 than the stem-joints beneath it, and is obviously what Schultze^ calls it, viz., "Eine 

 fiinfseitige, aus der Erweiterung des obersten Siiuleugliedes gebildete Platte." Unfortun- 

 ately we are not acquainted with the mode of development of the under-basals, as they 

 occur in no recent Crinoid ; but the analogy of the development of the other calyx- 

 plates indicates that they are primitively five separate plates, like their homologues in the 

 apical system of Ophiurids and Stai-fishes ; and a theory which would homologise them 

 with a plate that first appears as a simple ring, seems to me to run counter to all true 



' Ueber Plicatocrinus, he. cit., pp. 107, 108. ^ Revision, part i. p. 141. 



3 Einige Crinoideen und andere Thierreste des jiingeren Bergkalks im Gouvernment Moskan, Bull. Soc. Imp. des 

 Nat. Moscov, 1867, p. 28. 



* Op. cit, p. 15, Taf. ii. fig.'^. 1 a, 6 a. 



