REPORT ON THE CRINOIDEA. 185 
however, that I cannot agree with Wachsmuth respecting its nature. For, like that of 
Ichthyocrinus, it appears to me to represent the plated ventral perisome of the 
Neocrinoids ; while the ridges which radiate to the arm-bases seem to me to consist of the 
covering plates of the ambulacra. I do not deny that they may have been closed down, 
either temporarily as in the recent Pentacrinus wyville-thomsoni (Pl. XVII. fig. 6), or 
permanently as in Platyerinus. But I cannot imagine that they represent parts of a solid 
vault like that of Actinocrinus. 
I would say the same of Xenocrinus, of which Miller’ speaks as follows: “ Interradial and 
intersecondary radial spaces. . . . These long, narrow, depressed areas are covered with 
small plates, having a tubercle or short spine in the central part of each. There are 
more than seventy-five plates in each interradial area, and twenty-five or more in each 
intersecondary radial area before reaching the top of the cup, but the small plates 
continue over the margin of the vault, and undoubtedly cover it, and also more or less of 
the long proboscis, which is extended from the anterior or azygous side.” 
Wachsmuth denies that any Palzeocrinoid is known in which the existence of a solid 
vault has been disproved or cannot be traced by analogy; and also that there can be 
any homology between this solid vault and the ventral perisome (whether soft or plated) 
of a Neocrinoid. He has since admitted, however, that the radial pieces in the vault of 
Cyathocrinus and Platycrinus correspond to the ambulacral skeleton on the external 
surface of the body of recent Crinoids ; and I venture to think that in the case of Glypto- 
crinus, Reteocrinus, and Xenocrinus, and also of the Ichthyocrinidee, the resemblance to 
the Pentacrinidee, Apiocrinidee, and Comatulz is such as to leave no reasonable doubt that 
the so-called vault of these Paleocrinoids is homologous with the ventral surface of the 
body in the Neocrinoids. Except as regards Coccocrinus, however, I am not prepared to 
deny that the mouth was subtegminal, 7.c., concealed beneath the apical dome plates, 
which I regard as representing a permanently closed oral pyramid. When the presence of 
these plates has been demonstrated in Coccocrinus, I will admit that the “ Scheitelstiicke ” 
which Allman, Wachsmuth, Zittel, and myself have all considered as orals, belong to the 
interradial system, and do not surround an open mouth as the orals of Holopus, 
Hyocrinus, and Thawmatocrinus do. 
1 Journ. Cincinn. Soc. Nat. Hist., vol. iv. p. 72. 
(ZOOL. CHALL, EXP.—- PART XXX1I.—1884.) hi 24 
