REPORT ON THE CRINOIDEA. 161 
accidental one, and that I am inclined to attach too much importance to it ; and in that 
ease I should certainly agree with Wachsmuth in calling them secondary interradials. 
One point, however, is worth notice. The orals of Zhaumatocrinus, like those of 
Hyocrinus (Pl. V1. figs. 1-4 ; Pl. LVI. fig. 5), are only separated from the calyx plates 
by the thin band of perisome round the edge of the disk, which develops in the equatorial 
zone of the larva, concurrently with the increase in the diameter of the cup. These 
genera are thus in the condition of the advanced Pentacrinoid of Antedon rosacea, the 
oral circlet of which, owing to the increase in the size of the visceral mass, becomes 
detached from the summit of the primary radials ; and the space between the two series 
is filled by the perisome of the equatorial zone, which separates the right and left larval 
antimers. 
In the early stages of Hyocrinus, before this process had taken place, the orals would 
rest directly against the upper edges of the radials, as they do in Holopus (PI. IIL fig. 2), 
but in Thawmatocrinus they must rest against the primary interradial plates. They 
would thus be in precisely the same relative position as the “Scheitelstiicke” of Cocco- 
crinus; but I do not think that when a young Thaumatocrinus is found in this condition 
Wachsmuth will call the oral plates ‘secondary interradials ”. though he uses this term 
for the plates of Coccoerinus which I, like Allman and Zittel, consider as representing 
the orals of Neocrinoids, including 7) haumatocrinus. 
If then the “Scheitelstiicke” of Coccocrinus be oral plates, there are strong 
morphological reasons against the supposition that the ambulacra which pass in between 
them were closed by small marginal pieces, 7.c., by covering plates like those which occur 
so frequently on the arms and pinnules of many Neocrinoids (Pl. Ve. figs. 8-10; 
Pl. XIII. figs. 15,16; Pl. XVII. figs. 2-4, 7-9) and Paleeocrinoids, and on the summit 
of Cyathocrinus. Why should we invoke the existence of a “vault” over the orals of 
Coccocrinus, simply because it is a Palzocrinoid 4 There is nothing of the kind in the 
recent Holopus which dates back to the Chalk; while the allied genera Cotylecrinus, 
Eudesicrinus, and Eugeniacrinus are almost as old as the Mesozoic period. In no recent 
Crinoid, nor in the Pentacrinoid larvee of those species which have covering plates to the 
ambulacra do these plates rest upon the edges of the orals. They commence at the 
margin of the peristome which is covered in by the orals, but there are none bordering 
the edges of the grooves between these plates. 
It is partly, I believe, owing to his feeling the force of this objection that Mr. 
Wachsmuth prefers to consider the “ Scheitelstiicke ” of Coccocrinus as secondary inter- 
radials, rather than as orals. When he has found a specimen showing the small pieces at 
their edges, I shall probably agree with him. But for the present I am inclined to lay 
more stress on the resemblance of the “Scheitelstiicke” of Coccocrinus to the orals of 
Neocrinoids ; although, according to Wachsmuth," “ this resemblance is probably merely 
1 Revision, part ii. p. 17. 
(zoOL. CHALL. EXP.—PART xxxu.—1884.) li 21 
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