162 THE VOYAGE OF H.M.S. CHALLENGER. 
superficial, as the lateral grooves in Coccocrinus were evidently closed by additional 
plates as in other Platycrinidee, while they are open” in Neocrinoids. But the existence 
of these additional plates does not seem to me so evident as it does to him. He attempts 
to support his position by reference to a “close resemblance” between the summit 
of Coccocrinus and that of the Cyathocrinide, which he describes as follows :— Calyx 
surmounted by five large oral plates, with a central opening between them, and forming 
at their sutures five shallow ambulacral grooves converging toward the centre. Central 
opening covered by the apical dome plates, and the five grooves arched over by two rows 
of small immovable pieces alternately arranged.” 
The so-called oral plates of this description are those which Wachsmuth had previously 
ealled ‘consolidating plates,” thinking them to be homologous with the plates of the 
same name in Cupressocrinus. He subsequently came to the conclusion, as did Zittel 
about the same time, that they are homologous with the orals of the Pentacrinoid ; and 
he therefore also spoke of them by thisname. He likewise regarded the deltoid pieces of 
the Blastoids in the same way. I must plead guilty to having also adopted this view, 
which had much to recommend it at first sight. I did not do so, however, without con- 
siderable hesitation, on account of one morphological difficulty which it involved. For 
the ambulacra would then pass over and not between the edges of the oral plates, which 
would bear a double row of marginal pieces or covering plates continuous with those on 
the arm-grooves. This, as pointed out above, is contrary to the nature of the oral plates 
of Neocrinoids ; and the result of the correspondence on the subject between Mr. Wachs- 
muth and myself is that we can no longer regard either the deltoid pieces of the 
Blastoids or “the principal vault pieces” of Cyathocrinus (as Meek and Worthen call 
them) as representing the orals of Neocrinoids. I am now disposed to consider that 
“ Cyathocrinus and the Blastoids have but one interradial plate, which reaches up to 
the peristome.” Mr. Wachsmuth’s first criticism of this statement was that “it expresses 
exactly my views.” 
I believe, however, that his views have since undergone some further modifications, 
as he will himself explain in the forthcoming part (1i1.) of his Revision. 
But the question of the structural resemblance between Coccocrinus and Cyathocrinus 
is independent of the nomenclature of the plates. It is one of some importance in its 
bearing on the belief of Zittel and myself on the condition of the mouth in the former 
type and its relation to that of Neocrinoids. In the first place, as pointed out by Wachs- 
muth and Springer,’ Cyathocrinus has only one plate resting “against the incurved 
upper margins of the radials;” while in Coccocrinus the primary interradial bears a 
triangular plate, which they now consider as a second interradial, though formerly 
regarding it as an oral plate, as do Zittel and myself. The central opening in 
Cyathocrinus is much larger than in Coccocrinus, owing to the truncation of the 
1 Revision, part i. p. 68. 2 Tbid., part ii. p. 17. 
P Pp. Pp P 
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