196 THE VOYAGE OF H.M.S. CHALLENGER. 
based essentially on the presence or absence of a canaliculated structure in the calyx and 
arm plates.” The last of his three leading divisions, the Canaliculata, corresponds to the 
Articulata, Miiller ; but Chapman’s name does not appear to me to be so greatly superior 
to Miller’s that it could be adopted without hesitation. Platycrinus, Marsupites, and 
Uintacrinus have perforated first radials. They are, however, placed by Chapman 
among the Emedullata, in which “the calyx plates are without internal canals.” 
The absence of canals in the calyx plates is a character of very general occurrence 
among the Palzeocrinoids, and one which does not present itself in any adult Neocrinoid. 
But there are several Paleeocrinoids in which it does not occur at all, and it cannot there- 
fore be used as the principal “ differentia” for separating the older (Tessellate) from the 
younger (Articulate) Crinoids. 
Reasons have already been given for preferring the name “Neocrinoidea” for the 
latter group to either Stomatocrinoidea or Articulata. The second of these names is 
certainly founded upon a misconception, and I believe the same to be the case with the 
first one; while neither of them was ever properly defined by its author. The name 
Neocrinoidea is coming gradually into use; and as the essential differences between this 
order and that of the Palzeocrinoidea have already been discussed in Chapter X., it is not 
necessary for me to go into them again, though they may be conveniently put in the 
form of a definition. 
Order NEOCRINOIDEA. 
Crinoids with a regularly pentamerous calyx, which is generally without primary 
interradial plates, and except in one genus has no anal or azygous side. The calyx- 
radials are perforated, and are generally united to the succeeding plates by a muscular 
‘ articulation. The rays may remain simple, or divide from one to eight times, the first 
axillary being usually the second joint after the primary radials of the calyx. Orocentral 
plate probably never developed ;. orals, when present, may be limited to larval existence, 
or remain through life partially covering the peristome, but capable of being separated 
so as to open the mouth to the exterior. The oral surface of the visceral mass, 
with the ambulacra traversing it, may be more or less paved by plates, but is not in 
any way covered up and shut off from the exterior by a vault. 
