228 Mr. F. A. Bather on British Fossil Crinoids : 



number would be more correct. Tliis comparison sliows 

 tlie 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. 



Ayicd 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 pai-t 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 bracliianal ; 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 1»38, 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. Tiie totra- 



• Dr. P. II. Ciu-penter (Ann. & Mng. Nat. Hist. [G] vi. pp. 19, 20, July 

 1890) will not pevniil tho epithet "axillaiv" to be applied to anything 

 but an rt^Hi-o.^siclo fiiving ri.se to <///)<-brani'hes. Such restriction of a 

 word so citniuion in scienlilie description would be ve.vatious were it not 

 needless. An axil lies where an orjjan is given off from an axis, and 

 " axillary '' should have no deeper morphological signiticance. 



