III. Thenar ocrinus callipygus. 231 
of the ossicles along radial lines is often observable, as in 293 
Holcroft and 138 Mason College (Diagram 7). 
The Dudley specimen shows slight longitudinal ridges on 
its stem, especially at the proximal end ; and these as they 
cross the transverse ridges of the ossicles produce a slight 
cancellated pattern (Plate X. fig. 7). For the present, at all 
events, it is best to regard this as a mere individual variation. 
General Remarks. 
The most interesting feature of this genus is that in which 
it differs from other Fistulata, namely the low position of the 
Radianal. Indeed this one point alone separates it from 
nearly all other Crinoids, and appears of still further import- 
ance in connexion with various utterances of Messrs. Wachs- 
muth and Springer. Criticising the description of Garabo - 
crinus by E. Billings, they wrote : eC The anal area, .... 
according to Billings, is composed of three plates, the lower 
one resting upon the underbasals, which is in itself an anomaly 
such as is found in no other genus ” *. For the same reason 
they denied the correctness of Angelin’s description of Sageno - 
crinus , saying, u Angelin gives the number of basals (para- 
basals) as six, which is evidently a mistake, nor do we believe 
that the sixth plate represents an anal plate, as no plate of 
that kind has ever been observed below the line of radials ” f- 
Again in 1885 they wrote with even more decision, u There 
is not a single instance of Crinoids known to us where either 
a radial or an anal plate entered the basal ring ” J. There 
does not, however, seem to be any morphological objection to 
the sinking of an anal plate into the basal circlet, and in fact 
Messrs. Wachsmuth and Springer have prudently refrained 
from a priori argument. There can at any rate be no manner 
of doubt that the thing has happened in Thenar ocrinus^ and, 
rare though it be, there is nothing anomalous about it ; on the 
contrary, the sinking of the radianal, in common with the 
brachianal and anal series, is in perfect harmony with the 
views as to the origin of those plates put forward in Paper II. ; 
while the consequent widening of the anal area, enhanced as 
it is by the width of all the plates of the dorsal cup, is 
obviously correlated with the large size of the ventral sac, just 
as was explained on pp. 319 and 330 of the same paper. 
But if Thenarocrinus is not anomalous, neither is it unique. 
* Rev. I. (144), Proc. 1879, p. 367. 
t Rev. II. (202), Proc. 1881, p. 376, footnote. 
t Rev. III. (55), Proc. 1885, p. 277. 
17 * 
