REPORT ON THE CRINOIDEA. 157 
and its allies as forming “a free arch which braces the entire oral side of the body 
without the aid of oral plates.” 
The use of the term “aboral” as applied to the vault is somewhat unfortunate, for it 
actually does cover in the mouth; while the plates of the opposite or dorsal side of the 
body have generally been called aboral by writers on Echinoderm morphology. Wach- 
smuth himself applies this expression to the plates of the cup up to the level of the arms. 
In lke manner he gives the name “ apical dome plates”* to “a system of plates in the 
vault which occupy a position analogous to that of the apical plates of the calyx ;’ 
central plate, with a proximal ring of interradial, and a distal ring of radial plates disposed 
regularly around it. These must be carefully distinguished from the dorsocentral, basals, 
and radials, which are the apical plates of the calyx ; and, as mentioned above, have definite 
homologues in the apical system of Urchins and Stellerids. [See Appendix, Note A. ] 
The suggestion of Wachsmuth and Goette that the Paleocrinoids represent a 
comparatively early stage in Crinoid ontogeny, before the opening of the tentacular 
vestibule to the exterior, has been very generally accepted. But it must be borne in 
mind that though the Palzeocrincids may be considered as permanent larval forms with 
respect to the closure of the actinal side, yet that in other respects they have developed 
toa far greater extent than any Neocrinoid. The solid vault of an Actinocrinus is a 
Vaz os 
structure sui generis, unless, as I believe, its proximal ring of interradial plates is 
represented by the orals of a Neocrinoid. The extraordinary development of arms or of 
other appendages which we find in forms like Callicrinus, Pterotocrinus, Ollacrinus, 
Eucalyptocrinus, Crotalocrinus, &c., is entirely without a parallel among the more 
regular and symmetrical Neocrinoidea. We must be careful therefore not to make too 
much of the one or two embryonic characters presented by the Palsocrinoids, as com- 
pared with the facts of their great complexity of structure and immense variety of form. 
The simplest type of summit to be met with in any Paleocrinoid is that presented by 
the Devonian genus Haplocrinus, which remains permanently in the condition of a very 
early larva. For the orals, together with certain upward processes of the radials on 
which they rest, form a closed pyramid just as in an early Pentacrinoid. There are five 
openings which lead in beneath this oral pyramid and correspond to the points of 
attachment of the arms; but its apex is completely closed so that there is no external 
mouth. The lines of suture between its component plates are generally marked by deep 
grooves which descend from the closed apex to end below at the radial openings. 
Wachsmuth and Springer call them compartments for the reception of the arms, while 
they have been described by Zittel” as “nach unten geschlossene, nach oben offene 
Ambulacralfurchen.” 
This appears to me to be a mistake, and I do not see any reason for supposing that 
these orals were ever covered in by plates as he elsewhere suggests. 
1 Revision, part i. p. 28. 2 Paleontologie, p. 347. 
