MORPHOLOGICAL PART. 91 
surrounding it. He regarded the former as the actinal representative of the 
dorso-central or terminal plate of the stem, and the latter the representatives 
of the basals. He took the proximals to be the orals, believing with us that 
the posterior oral was divided into two plates. He said:* “The proximal 
dome plates rest directly against the calyx interradials, that on the posterior 
side being represented by two small plates with the anus between them ; 
while there is a more or less tubercular ring of radial dome plates outside 
them. These proximal dome plates thus correspond exactly to the orals of 
Symbathocrinus and Haplocrinus, covering in the peristome, and resting against 
the calyx plates, which in Platycrinus are the interradials, and not the upper 
edges of the radials, as in the simpler forms. . . . I cannot see what other 
view can be taken of the proximal dome plates which immediately surround 
the oro-central, than to regard them as orals; 7. ¢., as the actinal representa- 
tives of the basals, like the corresponding plates in Symbathocrinus. If this 
be admitted, it follows that the proximal dome plates of all Platycrinide, 
Actinocrinidxw and Rhodocrinidew are also homologous with the orals of Neo- 
crinoids.”’ + Carpenter’s oral theory was based almost entirely upon the 
hypothetical oro-central, — a plate before unknown in Echinoderm morpho- 
logy, —and the six proximal plates, which he assumed to be orals, although 
their morphological relations had never been established. 
The same view of the question was also taken by Etheridge and Car- 
penter,f and afterwards by Newmayr;§ while Zittel || supposed the orals 
to be unrepresented in all Platycrinidx, Actinocrinide, Rhodocrinidx, and 
Calyptocrinide ; though admitting their presence in some of the other 
groups. 
The above theory was laid aside by us in 1885, when we ascertained that 
the two smaller proximals, which we had supposed to represent the posterior 
oral, occupy a radial position, and therefore could not be orals. The struc- 
ture shows that these plates undoubtedly represent the two posterior radial 
dome plates, pushed to a position among the plates of the proximal ring by 
the anus, the three anterior ones retaining their position within the re- 
entering angles of the four larger proximals. This discovery was announced 
by us in Part II of the Revision, p. 47, and we designated the respective 
* Chall. Rep. Stalk. Crin., pp. 170 to 171. 
+ Dr. Carpenter’s views on this subject are fully set forth in the Chall. Rep. Stalk. Crin., pp. 158 
to 184. 
£ 1886. Catalogue of the Blastoidea, pp. 66 to 75. 
§ 1889. Die Stamme des Thierreiches, p. 448. 
|| Handb. ‘der Paleont., I, p. 332. 
