REPORT ON THE CRINOIDEA. 231 
are relatively large, but otherwise of the usual character, with paired fosse for the 
muscles and interarticular ligaments (PL VIa. fig. 15, rm’ and lv’), and the single one 
beneath the articular ridge for the reception of the dorsal ligament (/d’). The second 
radials (Pl. VII. figs. 5, 5a) are broad, flattened, and somewhat quadrate in form, with 
a more or less distinct medio-dorsal convexity (Pl. VIIb. fig. 6, R2) and a well-marked 
furrow in the middle line of the ventral surface (Pl. VII. fig. 5a). The proximal face 
resembles that of the first radials, which is high relatively to its width (Pl. Vila. fig. 15), 
while the articular surface at the distal end is low and much extended laterally. The 
axillaries 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 
axillaries articulate without the sntervention 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 (Pl. VII. figs. 4, 4a; Pl. Via. 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 interradial diverticula of the 
gut (Pl. VID. fig. 7, Rs). 
According to Sir Wyville Thomson, the two outer radials of Bathycrinus gracilis and 
Bathycrinus 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 
to) 
at all; nor, as I believe, in any species of the genus. The distal face of the second 
radial isshown in Pl. VIIa. fig. 16. Apart from its external form, it has a general resem- 
plance 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 Comatulee, 2.e., there 
is a vertical articular ridge which separates the two fosse lodging large bundles of 
ligament (i’). 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 Comatule, 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 sufficient to show that the plainness of the syaygies in Pentacrinus or 
Rhizocrinus, and the striation so common in the Comatule, are altogether absent, 
being replaced by distinct ridges and fosse. In describing Bathycrinus gracilis, Sir 
Wyville Thomson’ pointed out that “the first brachial is united to the second by a 
1 Nyt Mag. f. Naturvidensk., Ba. xxiii. p. 6. 2 Proc. Roy. Soc. Edin., 1872, vol. vii. p. 773. 
