REPORT ON THE CRINOIDEA. 185 



however, that I cannot agree with Wachsmuth respecting its nature. For, like that of 

 Ichthyocrmus, 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 ivyviUe-thomsoni (PI. XVII. fig. 6), or 

 permanently as in Platycrinus. 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 Palseocrinoid 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 

 Cyathocrintis 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- 

 cnnus, Reteocrmus, and Xenocrinus, and also of the Ichthyocrinidse, the resemblance to 

 the Pentacrinidse, Apiocrinidse, and Comatulae is such as to leave no reasonable doubt that 

 the so-called vault of these Palseocrinoids 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, i.e., 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 AUman, 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 Holojms, 

 Hyocrinus, and Thaumatocrinus do. 



1 Journ. Cincinn. Soc. Nat. Hist, vol. iv. p. 72. 



(ZOOL. CHALL. EXP. — PART X3LSII. — 1884.) li 24 



