228 Mr. F. A. Bather on British Fossil Crinoids : 
number would be more correct. This comparison shows 
the greater extent of food-collecting surface possessed by the 
older and non-pinnulate form : the advantage of Encrinus lies 
of course in its greater compactness. Neither of these calcu- 
lations takes into account the covering-plates, the addition of 
which would treble or quadruple the numbers. 
Anal structures : — Radianal (R ; ) , an irregular pentagon, the 
greatest width of which is equal to its greatest height ; rests 
on r. post. IB., between post. B. and r. post. B. ; supports 
on its right upper side part of r. post. R., and on its left 
upper side the Brachianal. 
Brachianal ( x ) rather wider than high, in outline like a 
radial, the distal edge forms the longest side ; rests on post. 
B and R/ ; is bounded on left by 1. post. R., and on right by 
r. post. R. ; supports in the middle a wide low plate, which 
we may regard as a second brachianal ; and on either side is 
touched by smaller plates which are probably derived from 
the tegmen. 
This disposition of the anal plates is best shown by the 
Mason College specimens 138, 144, and 153, and by 431 
Holcroft ; it is seen, but owing to fracture not so clearly, in 
293 Holcroft. The diagram of Thenarocrinus that forms 
fig. 14 of plate xiv. in the first half of Paper II. (‘ Annals,’ 
ser. 6, vol. v. April 1890) was constructed from the evidence 
of the British Museum specimen 57478 a ; since this fossil is 
much flattened the anal plates, which occur at its extreme 
edge, are displaced and fractured, so that the diagram, though 
correct in the more important points, is not absolutely accur- 
ate as to details [cf. Diagram 6). 
The connexion of the ventral sac with the anal plates is 
seen in specimens 57478 a B. M., 138, 144, and 153 Mason 
College, and in 293 and 431 Holcroft. No one of these 
specimens shows all the details, besides which they vary 
slightly, but all conform in essential structure with Dia- 
gram 1. The Second Brachianal rests on the first brachianal 
just as the costals rest on the radials ; it is pentagonal and 
axillary *. The plates of the ensuing distichous series alter- 
nate slightly, the suture separating them being a zigzag and 
the plates consequently hexagonal. The second plate of the 
right-hand series is axillary, and it is probable that the same 
is the case with the similar plate on the left. The tetra- 
* Dr. P. H. Carpenter (Ann. & Mag. Nat. Hist. [6] vi. pp. 19, 20, July 
1890) will not permit the epithet a axillary” to be applied to anything 
but an arm- ossicle giving rise to ar m-branches. Such restriction of a 
word so common in scientific description would be vexatious were it not 
needless. An axil lies where an organ is given off from an axis, and 
axillary " should have no deeper morphological significance. 
