170 THE VOYAGE OF H.M.S. CHALLENGER. 
Crinoid. Did it appear, it would only be in the way, and have to undergo resorption to 
a greater or less extent, just as the dorsocentral of many Urchins is more or less com- 
pletely resorbed after the appearance of the anus. 
As regards the recent Crinoids, therefore, the embryological evidence clearly indicates 
that the basals of the abactinal system are represented in the actinal system by the orals. 
The former are within the ring of radials and next to the dorsocentral; and it seems 
therefore only natural to regard the six proximal interradial plates surrounding the 
central piece (orocentral) in the vault of a Paleocrinoid as representing oral plates. 
Wachsmuth admits that Zittel was right in regarding the interradial plates which 
form the dome of Haplocrinus as representing the orals of Neocrinoids; and he takes 
the same view of the interradial plates in the dome of Symbathocrinus. I should have 
thought therefore that he would have given a similar interpretation of the summit plates 
in Platycrinus and Culicocrinus. Those of the latter genus were described by Miiller as 
follows :—‘‘ Der Scheitel besteht aus 5 Tafeln, welche dicht an einander schliessen durch 
Nihte und anderseits bis an die Arme und die Interradialia reichen, sie stehen iibrigens 
interradial, so dass jedes Interradiale zu einem der funf Scheitelstiicke stimmt. Der 
Mund (ef. anus) befindet sich seitlich in einem Interradius zwischen dem Interradiale 
und entsprechenden Scheitelstuck. Auf jeder der 5 Scheiteltafeln erhebt sich ein 
kurzer Dorn.”* Wachsmuth calls these ‘ Scheitelstiicke” of Miiller’s the proximal vault 
pieces, and suggests that “ probably his largest plate includes four plates, the spiniferous 
central vault piece, the two proximal vault pieces, and a small anal plate between them. 
The four large proximal vault pieces, each crowned with a spine, are no doubt correctly 
represented. Those few plates oceupy the greater part of the summit, leaving but little 
space for the radial dome plates, which as yet are unknown.” ? 
I think myself that this suggestion is totally unnecessary ; for the five summit plates 
appear to me to form a closed oral pyramid in which the plate on the anal side is somewhat 
wider than its fellows, but not divided into two as in the Actinocrinide and Platyerinide. 
Culicocrinus has the proximal dome plates resting against the calyx interradials, just 
as the orals do in Coccocrinus. But no distal ring of radial dome plates is known in 
this genus. This advance in complexity is presented by certain forms of Platycrinus from 
the Carboniferous limestone, both at Burlington and at Bolland. Miiller gave some 
figures of the latter under the name of Platycrinus ventricosus, Goldfuss, which is 
certainly wrong;? and I have examined several specimens in the British Museum collee- 
tion which are in this comparatively primitive condition. The proximal dome plates rest 
directly against the calyx interradials,* that on the posterior side being represented by 
two small plates with the anus between them; while there is a more or less tubercular 
1 Verhl. d. Naturhist. Verein. d. preuss. Rheinl., Bd. xii., Jahre. 1855, p. 23. 
2 Revision, part ii. p. 62. 3 Bau des Pentacrinus, loc. cit., Taf. vi. figs. la, 1b. 
4 Tt is only just to Mr. Wachsmuth for me to state here that he was the first to direct my attention to the fact that 
Platycrinidé exist with the proximal dome plates resting directly against the calyx interradials, two individuals in this 
