MORPHOLOGICAL PART. 129 
truncate upper face of plate z. The plate to the right lies at a somewhat 
higher level than the one to the left, and does not touch w, owing to the 
greater length of the compound radial, while that to the left touches it 
slightly. The three plates form part of the free tube, and each one is fol- 
lowed by a vertical row of other tube plates. 
Comparing this structure with that of Heterocrinus (Fig. 10), Eetenocrinus 
(Fig. 11), and Hybocrinus (Fig. 8), we find that the plate ¢ in all these forms 
takes practically the place of the three plates (¢¢¢) in Dendrocrinus. In 
either case the plates constitute the lower tube plates, and rest — the one 
as well as the three — upon the sloping upper faces of the two posterior 
radials; but while the three plates of Dendrocrinus are supported by a special 
anal plate, the radials of Heterocrinus, etc., meet underneath, and the anal is 
unrepresented. In Dendrocrinus, which has an extremely large anal tube, 
the anal x is well represented ; while in the three other genera, in which the 
tube is narrow, and the outer edges of the radials are sufficient to support 
it, that plate is wanting. If it were true that the plate ¢ in Heterocrinus 
represents the plate x, and sunk down in palxwozoic times to the basals, as 
supposed by Bather, the plate x would be represented twice in Dendrocrinus 
Casei, once by x, and again by ¢, both plates being present and in place. 
Bather makes the statement (p. 331) that the “ brachianal”’ and the 
plates succeeding it in regular series, are to be regarded as brachials, but 
that the remaining plates of the sac are nothing more than plates deposited 
in an extension of the ventral perisome, and in conformity with this he 
? 
has called the superradial of Jocrinus an axillary plate. The term “ axillary’ 
in Crinoid terminology is given exclusively to plates of the rays, and every 
axillary is followed necessarily by a branching of the arm. Bather in using 
that term must have supposed that the so-called brachianal, and the plates 
succeeding it, are parts of a modified arm, which in geological time became 
incorporated into the sac, for in no other way could we understand why he 
called it an axillary. He has probably been misled by the angularity which 
occurs upon the upper face of the superradial, or by the form of the plates 
succeeding it to the left, and the slanting position of the posterior arm to the 
right. In that case he overlooked that the radials in Actinocrinus also have 
sloping upper faces, and yet that those plates are not axillaries, supporting 
as they do at one side a costal, but an interbrachial at the opposite side ; 
and it did not occur to him that such might be the case also in Jocrinus. 
Examining the anal interradius as it appears in the Camerata among the 
17 
