162 THE VOYAGE OF H.M.S. CHALLENGER. 



superficial, as the lateral grooves in Coccocrinus were evidently closed by additional 

 plates as in other Platycrinidse, 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 Cyathocrinidse, 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 hj 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 

 called " consolidating plates," thinking them to be homologous with the plates of the 

 same name in Cupressocrimis. 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 this name. 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 difiiculty which it involved. For 

 the ambulacra would then pass over and not hetween 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 AVorthen call 

 them) as representing the orals of Neocrinoids. I am now disposed to consider that 

 " Cyathocrimis 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 (iii.) of his Ee vision. 



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 

 Cyathocrimis is much larger than in Coccocrinus, owing to the truncation of the 



' Reviaiou, part i. p. 68. ^ ]]ji±^ yatI ii. p. 17. 



