90 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
terior side to a nearly central position. The description of the ventral plates 
of this genus in the Revision, Part III., p. 37, was incorrect as to the small 
pieces around the five summit plates, the appearance of which was produced 
by cracks and not sutures. Specimens of better preservation show positively 
that the ventral surface is occupied exclusively by the five large plates. 
Pisocrinus, as shown by a specimen of P. pilu/a in our possession from Dudley, 
England, has a similar structure. Among the Camerata five large summit 
plates are known to exist only in Coecocrinus and Culicocrinus, the plates 
of the former being equal (Plate III., Fig. 14), those of the latter slightly 
unequal. 
As the large central plate, when it occurs, occupies approximately the 
same position as the oral opening of recent Crinoids, it seemed plausible that 
the orals, if present at all, should be looked for in the Camerata among the 
plates of the proximal ring; but on examining the structure, it was found 
that only the four larger plates could be compared with the five orals of 
recent forms; so the question arose, what had become of the corresponding 
fifth plate ? 
Wachsmuth, in 1877,* directed attention to the two plates of the same 
ring adjoining the four larger ones, and suggested that these two plates 
taken together were probably equivalent to one, being split into two by the 
anus, and that the six plates represented morphologically but five. The 
plates were not, however, regarded by him as the orals; he thought the 
whole ventral covering of the earlier Crinoids was structurally distinct from 
the disk of recent ones. 
A similar view of the subject was taken by us in the following year.t 
We assumed that the plates of the dorsal cup and those of the tegmen were 
parallel structures ; that the central plate was represented in the dorsal cup 
or abactinal side by the infrabasals, the six proximals by the basals, and that 
other plates of the tegmen represented the radials and interradials. No 
comparison was then made by us of these plates with the plates in the disk 
of recent forms; but this was done in 1881,+ when we suggested that the six 
proximals represented the orals. 
Dr. P. H. Carpenter, like ourselves, recognized in the Camerata a central 
plate, for which he proposed the name “oro-central,” and six proximals 
verified our observation, and held the plate to be homologous with the so-called central plate of the Camerata, 
(Chall. Rep. on the Stalked Crinoids, p. 158). 
* Amer. Journ. Sci. and Arts (series 3), Vol. XIX. pp. 186-187. 
+ Revision, Part I., p. 28. 
t Revision, Part II. p. 17 (Proceed. Acad. Nat. Sci. Phila., p. 191). 
