REPORT ON THE CRINOIDEA. 231 



are relatively large, but otherwise of the usual character, with paired fossae for the 

 muscles and interarticular ligaments (PL Vila. fig. 15, rm' and W), and the single one 

 beneath the articular ridge for the reception of the dorsal ligament (Id'). The second 

 radials (PI. VII. figs. 5, 5a) are broad, flattened, and somewhat quadrate in form, with 

 a more or less distinct medio-dorsal convexity (PI. Vllb. fig. 6, R2) and a well-marked 

 furrow in the middle line of the ventral surface (PI. VII. fig. 5a). The proximal face 

 resembles that of the first radials, which is high relatively to its width (PI. Vila. fig. 15), 

 while the articular surface at the distal end is low and much extended laterally. The 

 axiUaries are more or less pentagonal, with a forking median ridge on the flattened dorsal 

 surface. The ventral surface is flattened like that of the second radial, with which the 

 axiUaries articulate without the intervention of muscles. But the lateral margins of the 

 median ventral furrow rise gradually from the distal to the proximal end of the joint, 

 where they are produced into more or less expanded, wing-like processes which project 

 forwards over the first brachials (PI. VII. figs. 4, 4a; PI. Vila. fig. 17). The bases of 

 these serve for the attachment of the muscles and ligaments which unite the axillaries 

 and first brachials, while their upper portions support the iuterradial diverticula of the 

 gut (PL Vllb. fig. 7, E3). 



According to Sir Wyville Thomson, the two outer radials of Bathycrinus gracilis and 

 JBathycrinus aldrichianus are united by syzygy ; while Danielssen and Koren make the 

 same statement respecting Bathycrinus carpenteri} This is not really the case, how- 

 ever, and as a matter of fact there are no true syzygies in Bathycrinus aldrichianus 

 at all ; nor, as I believe, in any species of the genus. The distal face of the second 

 radial is shown in PL Vila. fig. 16. Apart from its external form, it has a general resem- 

 blance to the corres ponding face of the second radial in Pentacrinus decorus, Penta- 

 crinus naresianus (PL XXX. fig. 1 ; PL XXXIV. fig. 6) and the Comatulse, i.e., there 

 is a vertical articular ridge which separates the two fossae lodging large bundles of 

 ligament [W). But in Bathycrinus a third and smaller bundle of ligament is inserted 

 into a deep pit (Id') at the lower or dorsal end of the vertical articular ridge. The 

 proximal face of the third radial is of the same character ; and in reality the union of 

 these two joints, instead of being an immovable syzygy, is a modification of the bifascial 

 articulation permitting lateral movement only, which is so common in the Comatulse, and 

 is also characteristic of four recent species of Pentacrinus. Externally this form of 

 articulation looks very much like a syzygy, as the joints are brought into closer connec- 

 tion than when they are united by a pair of muscular bundles ; but a glance at their 

 apposed faces is sufiicient to show that the plainness of the syzygies in Pentacrinus or 

 Rhizocrinus, and the striation so common in the Comatulse, are altogether absent, 

 being replaced by distinct ridges and fossae. In describing Bathycrinus gracilis, Sir 

 Wyville Thomson^ pointed out that " the first brachial is united to the second by a 



1 Nyt Mag.f. NaturvidensL, BJ. xxiii. p. 6. ^ Proc. Roy. Soc. Edin., 1872, vol. vii. p. 773. 



