■REPORT ON THE CEINOIDEA. 61 



which they now possess. There arc no true pinnules in Cyathocrinus proper, but only 

 repeatedly branching arms, which must therefore have contained the genital glands ; and 

 each of the branches borne by one of the lower axillaries may fork again several times, so 

 that they cannot be compared to the long, undivided pinnules of Ilyocrinus (PI. VI. 

 figs. 1,2). In Poteriocrinus, on the other hand, the successive arm -joints bear pinnules 

 which are not specially different from those of Neocrinoids ; while the mode of branching 

 of the arms resembles that characteristic of Pentacrinus miillerl, and more especially of 

 Extracrinus, the axillaries being generally limited to the outer arms of the ray, and 

 having unequal distal faces. ^ 



It is in the curious genus Barycrinus, which was separated from Cyathocrimis by Mr- 

 Wachsmuth, that we find the nearest approach to the pinnule-arrangement of Ilyocrinus. 

 According to Wachsmuth and Springer" "all the main arms, instead of Ijifurcating, 

 give off" at regular intervals, alternately on opposite sides, and from the inner margins of 

 the plates, short, rounded, simple armlets, which in most species throw ofi" secondary 

 branches as in Botryocrinus, and these armlets here as there, probably performed the 

 office of pinnulje." Barycrinus hoveyi, var herculeus, M. and W., is one of the excep- 

 tional species in which the armlets are simple and without secondary branches. The 

 excellent figure of it which is given by Meek and "Worthen^ shows these armlets 

 to come off alternately on opposite sides just as in Ilyocrinus, but from every second 

 joint, instead of from every third (PI. VI. figs. 1, 2). They have unfortunately never 

 been found in a perfect condition ; and we cannot tell therefore whether they reached 

 to the level of the top of the arms proper as in Ilyocrinus, though Meek and AVorthen's 

 description seems to indicate that such is the case. 



The difference between these armlets of Barycrinus herculeus and those of Extra- 

 crinus is that the former seem to bear no pinnules as the latter do, and must therefore 

 have contained the genital glands ; while they come ofi" alternately from opposite sides of 

 the main arm-trunk, and not from its inner one only as in Extracrinus. 



We have seen that the pinnule of a Neocrinoid is practically a reduced copy of an 

 arm, but modified by the great development of the fertile portion of the genital gland 

 which it contains, that part of the gland which is confined to the arm being usually 

 sterile and known as the " genital cord " or " rachis " (PL Vc. fig. 1 ; PI. Villa, figs. 4, 5 ; 

 PI. LX. fig. 6—rjc.). 



Although it would seem improbable that the pinnules of Palseocrinoids are essentially 

 different in nature from those of the Neocrinoids, Messrs. Wachsmuth and Springer 

 have attempted to show that the small alternating plates covering the brachial ambu- 

 lacra of Cyathocrinus are homologous with the pinnules of the Actiuocrinida3 and 

 Platycrinidje. These are long, comparatively slender, and closely arranged side by side 



1 See p. 277. ' Revision, part i. p. 101. 



^ Palu'ontology of Illinois, vol. v. pi. xiii. fig. 2. 



