MORPHOLOGICAL PART. 89 
While thus among recent Crinoids the orals are readily recognized, their 
identification among Paleozoic forms has been the subject of much contro- 
versy. Allman* in 1863 expressed the opinion that the group of plates in 
the centre of the vault of many Palocrinoids is a representative of the sim- 
ple oral system of the young Comatula ; but as those plates often consist of 
more than five, it was not made clear to which particular ones his homology 
applied. In most Paleozoic Crinoids there is no oral opening, and the 
arrangement of the plates at the summit is irregular and quite variable. 
This is the case particularly among the Camerata, in which the median 
portions of the disk are generally occupied by a large, centrally located 
plate, surrounded by eight or nine others, of which four are large and 
similar in form and size. These four larger plates are directed toward 
the anterior side of the disk, forming at their outer edges re-entering 
angles, which are filled by three rather large plates, radially disposed ; 
while the four or five smaller plates of the proximal ring are directed 
posteriorly, and are followed by numerous more or less irregular pieces, 
directly or indirectly connected with the anus (Plate IIL, Figs. 17, 18, 20, 
21, 22, and 25). Occasionally the larger plates are separated from one 
another by small, supplementary pieces (Plate UI., Fig. 23). This is the 
case in some of the larger species, in which the small pieces were intro- 
duced in the growing Crinoid. There are also species in which the larger 
plates are not represented at all, and the whole ventral disk is composed 
of minute pieces without definite arrangement, leaving only an opening 
for the anus (Plate III., Fig. 24). 
The interpretation of these plates has proved the more difficult because 
in other groups, notably the Larviformia, the tegmen consists of but few 
pieces, which have a different arrangement. In Allagecrinus and Myrtilo- 
erinus (Plate II., Fig. 15), the whole ventral surface is covered by five large 
interradial plates, resting upon the superior edges of the radials, exactly as 
the orals in the Pentacrinoid larva of Antedon, Haplocrinus (Plate IIL. Fig. 
14) has five similar plates, which were at one time supposed to surround a 
small central plate.; © Symbathocrinus (Plate IIIL., Fig. 25) has a pyramid of 
five large plates, four of them resting upon the edges of the muscle plates of 
the radials, and partially surrounding a larger one, wedged in from the pos- 
* Trans. Roy. Soc. Edinb. Vol. XXIIT., pp. 245-251. 
+ Our supposed discovery of this plate in a specimen of Haplocrinus mespiliformis proved afterwards to 
be a mistake, due to the peculiar fractures in the specimen. Carpenter, to whom we submitted the specimen, 
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