134 



P. H. CAEPENTEE OK TWO NEW CEINOIDS EEOM 



faces are much reduced and quite insignificant, while in Ehizocrinus 

 they are wide, low, and separate, and more like those of Milleri- 

 crinus, enclosing a wide central funnel. 



In both species of Mesocrinus, however, and especially mM.suedicus, 

 the articular faces are much higher relatively to their width, are in 

 contact for the whole length of their sides (figs. 2 a, 7 a), and have 

 distinct muscle-plates, which stand up around the opening of the 

 small central funnel. These are largest and best developed in M. 

 suedicus, but are distinctly recognizable in Geinitz's figure of M. 

 Fischeri. 



These features are eminently characteristic of the Pentacrinidse 

 and Comatulidse, though I have seen no calyx of Pentacrinus which 

 could be said to be precisely like that of Mesocrinus. But then no 

 two Pentacrinus-calices that I have seen are precisely like one 

 another ; for they differ very much among themselves, not only in 

 the relative development of the basals, but also in the shape and 

 proportions of the outer surface of the radials and of their articular 

 faces. At the same time it must be remembered that we are only 

 just beginning to become acquainted with these modifications ; for 

 neither species nor individuals of living forms are at all abundant 

 in collections, much less are they available,' for anatomical investi- 

 gation. The calyx of Mesocrinus Fisclieri. (fig. 2) finds its nearest 

 ally in that of P. WyviUe-Thomsoni*. It is in a side view that 

 the resemblance is most evident, the chief point of difference being 

 the greater height of the radials and of their articular faces in 

 Mesocrinus. These features are more marked, however, in P. 

 asteriaf ; but in this species the basals are small, and do not meet 

 laterally as they do in Mesocrinus. Except in this point the calyx 



superieure ne servait pas de point d' attache" (loo. cit. p. 32). I regret that I 

 cannot altogether agree with this opinion of the distinguished Swiss palaeon- 

 tologist, who must have been unfortunate in some of the specimens he examined. 

 The large concave surface in which the second radials of Apiocrinus. rest is some- 

 times an expansion of what in recent Crinoids^is the dorsal fossa lodging the elastic 

 ligament. This is well shown in de Loriol's own figures of the ventral aspect 

 of the first radials of A. Meriani (pi. ii. figs. 4a, ba), and also in d'Orbigny's 

 figure of A. Murchisonianiis (pi. vi. fig. 7). The central end of this large fossa 

 is bounded by the transverse articular ridge pierced by the opening of the 

 central canal ; and rising up from this ridge so as to form a part of the rim of the 

 central funnel are larger or smaller plates for the muscle- and ligament-fossae. 

 In some specimens of Apiocrinus in the national collection these fossse are re- 

 latively large and are separated by a well-marked ridge ; but in most species 

 they are greatly reduced in size, as is also frequently the case in Millericrinus. 

 In the latter genus the dorsal fossa never reaches the enormous size that it does 

 in Apiocrinus, and, though it is sometimes relatively large (as in some Comatulce), 

 it is occasionally comparatively small. 



I am not prepared to say, however, that no Apiocri?izis had the first and second 

 radials united otherwise than by muscles and ligaments. They must, in some 

 cases, have been joined by a syzygy, e.g. Ap. Parhinsonii (d'Orbigny, pi. v. fig. 6) ; 

 but such cases are very anomalous; for in the other Articulate Crinoids 

 syzygial union, though common enough between the second and third radials, 

 never takes place between the first and second. Even in Marsupites there is a 

 distinct articular facet on the first radials. 



* Journ. Linn. Soc, Zool. vol. xv. pi. xi. fig. 23. 



t Journ. Linn. Soc, Zool. vol. xv. pi. xi. fig. 21. 



