160 THE VOYAGE OF H.M.S. CHALLENGER. 
they might then haye been lost after the decay of the perisome uniting them. Those of 
Holopus were retained in the dry specimen which was figured by Pourtalés,’ and 
subsequently by Sir Wyville Thomson ; and the condition of the Palaeozoic Coccocrinus 
seems to me to be entirely explained by that of the recent Holopus. 
Wachsmuth and Springer’ describe it as follows :—‘ In well preserved specimens of 
Coccocrinus, the vault is constructed of five large oral plates, which rest upon five 
interradial pieces. The oral plates are not in contact laterally, but leave five slits, which 
in the fossil have no floor nor covering, and leave an open space in the centre.” They 
are strikingly similar to the orals of the recent Hyocrinus (Pl. VI. figs. 1-4), as has been 
pointed out by Zittel ; and the resemblance to the orals of Holopus (PI. IIT. fig. 2) is still 
greater, as the latter rest directly against the calyx plates, which is not the case in 
Hyocrinus. In both the recent forms and also in Thawmatocrinus (Pl. LVI. fig. 5) the 
clefts between the triangular oral plates are open and uncovered, as in Coccocrinus. 
Schultze® follows Roemer in thinking that these slits do not penetrate into the cavity of 
the calyx; but that they were hollows for the reception of the arm bases, as in 
Eucalyptocrinus. But Wachsmuth, having examined Schultze’s specimens, states 
distinctly that these grooves have no floor. He says in the Revision (part 1. p. 17) that 
“the similarity to Hyocrinus is probably merely superficial, as the lateral grooves in 
Coccocrinus were evidently (why ?) closed by additional plates as in other Platycrinidee, 
while they are open in Hyocrinus.” Again “it is evident that the central space and 
open furrows were covered in the animal as in similar genera.” The oral plates “do not 
join laterally nor in the centre, but leave a median space and lateral slits, which in perfect 
specimens were doubtless closed, the one by the apical dome plates and the slits by small 
marginal pieces.” . . . . “In Coccocrinus a covering of the ambulacral groove has not 
yet been observed, but, judging from the fissure between the oral plates, it probably rested 
just upon their edges, and formed an intermediate link between the vault structure of 
the Cyathocrinidee and Platycrinide.”* 
When Wachsmuth wrote the passages which have been quoted above, he held, like 
Zittel and myself, that the five large triangular plates which rest on the primary inter- 
radials of the calyx are homologous with the orals of recent Crinoids. He has since, 
however, come to the conclusion that ‘‘ Coccocrinus had externally no oral plates, its so- 
called orals are secondary interradials, and mouth and food-grooves were covered by 
supra-oral plates” (Extract from Letter). I must confess that I greatly doubt the 
existence of this additional covering in Coccocrinus, which seems to Wachsmuth so 
evident; for I find it difficult to believe that the “‘ Scheitelstiicke,” as Schultze called 
them, are not oral plates like those of the Neocrinoids. Itis of course possible that their 
resemblance to the orals of Holopus, Hyocrinus, and Thaumatocrinus is simply an 
1 Hassler Crinoids, pl. x. fig. 9. * Revision, part ii. pp. 17, 58. 
3 Op. cit. p. 89. 4 Revision, part ii. pp. 17, 30, 58, 59. 
