REPORT ON THE CRINOIDEA. 163 



principal vault pieces or interradials, as they were also called by Meek and Worthen/ 

 The grooves which converge upon it are not like those of Coccocrinus " which have 

 no floor," ^ but they are formed at the sutures of the interradials, i.e., the apposed edges 

 of these plates are bevelled away so as to form a groove with the suture in the middle of 

 its floor. 



According to Wachsmuth and Springer,^ the central space " in perfect specimens is 

 completely covered by the apical dome plates. The food-groove and ambulacral canal 

 are also arched over solidly by two rows of alternate plates which connect with the 

 movable covering of the arm furrow." The existence of these marginal alternating 

 plates has yet to be proved in Coccocrinus, and until this has been done, the resemblance 

 between this type and Cyathocrinus does not seem to me to be very " close," for while 

 the arm-grooves of CyatJioc7'inus are continued towards the peristome over the united 

 edges of the interradials, this is by no means the case in Coccocrinus ; and there is no 

 groove on the ventral disk at all, any more than there is in Holo^Jus, or in any young 

 Crinoid before the separation of the orals and radials by the expansion of the equatorial 

 zone. The fact that the principal vault pieces of Coccocrinus are not united laterally, as 

 is the case in Cyathocnnus, seems to me to he one of very considerable morphological 

 importance. It must of course be remembered, as Wachsmuth has pointed out in other 

 cases, that the absence of a covering to the central space and its radial clefts in the fossil 

 Coccocrinus is no proof that it was not present during life as in Cyathocrinus. But the 

 two genera are not in the same morphological condition, and all that we hnoiv about 

 Coccocnnus goes to indicate its resemblance to Holopus with open slits between the 

 orals and an uncovered mouth. Wachsmuth,* however, states that he has " yet to 

 discover a single palaeozoic genus in which a special oral aperture has been identified, or 

 in which the existence of a solid vault has been disproved, or cannot be traced by 

 analogy." I believe, on the contrary, that the sjjecial oral aperture is to be found in 

 Coccocrinus as in Holopus, and that it is pushing analogy too far to assert the existence 

 of an as yet undiscovered vault in this genus. 



If then, as I believe, there was an unobstructed mouth in Coccocrinus as in Holopus, 

 I cannot agree with Zittel's association of this type with Haplocrinus, which had a closed 

 oral pyramid. 



Wachsmuth and Springer ^ place Coccocrinus near Platycrinus. "The two genera 

 are identical in the construction of the calyx, and the summit really forms the only 

 distinction between them." To this point I shall return. Coccocrinus, hke the recent 

 Holopus, seems to me to be permanently in the condition of a Crinoid larva in which the 

 orals have not yet moved away from the radials, though separated from one another. 



Haplocrinus and Symbathocrinus are permanently in the condition of an unopened 



^ Palaeontology of Illinois, vol. v. pi. ix. fig. 13. ^ Revision, part ii. p. 58. 



8 Revision, part i. p. 84. ■• Amcr. Journ. Sci. and Arts, vol. xiv. p. 190. ' Revision, part ii. p. 58. 



