10 THE VOYAGE OF H.M.S. CHALLENGER. 
muscles are ever found between the second and axillary radials of any Neocrinoid except 
Ludesicrinus (p. 215), nor (except in Metacrinus) between the first and second brachials, 
unless the latter be a syzygial joint. In the aberrant Metacrinus, however, the second 
radial is a syzygial joint (PI. XII. figs. 7-10) and the axillary is usually either the fourth or 
the sixth radial (Pl. XII. figs. 3,4; Pl. XX XIX. fig. 1; Pls. XLIL, XLII, XLV., XLVI, 
XLVITI—LI.); and there is usually a syzygy in the third joint after each successive axillary, 
just as in the free arms of most Comatulz. But the first two joints are united by muscles 
instead of by ligaments, as in the Comatulz ; and I have not met with any instances of 
bifascial articulation in the arms of this genus, which have nothing but syzygies and 
muscular unions like the arms of Actinometra solaris or Actinometra typica. 
Each pinnule has a muscular attachment to the arm-joimt which bears it (Pl. Ve. 
news El Villa. fie. 216 PloX Vil fig: bs. Pl. XX Xe, cigs) Wa, 12a3 Pl) XLT: ; 
fic. 11; Pl. XLVII. figs. 11, 12); while in Metacrinus and some tropical Comatule the 
lower joints of the pinnules are united by muscles instead of by ligaments or suture 
only (Pl. XIII. fig. 12). 
The articular face of a joint which is connected with its successor by muscular 
bundles presents a variety of fossee separated by intervening ridges, that are frequently 
somewhat ill defined (Pl. VIla. figs. 15, 17, 18, 19, 21, 28; Pl. X. figs. 1-4; Pl. XII. 
figs. 3-6, 8, 9, 12, 15, 19, 20, 23; PL XXI. figs. la. 1b, 2a, 2b, 3b, 4b, 5c, 6d, &c.). 
Beneath its upper and lateral edges lie the two fossee in which the muscular bundles are 
attached (Pl. VIla. fig. 15, rm’). They are sometimes separated by a vertical ridge as 
on the first radials of Antedon phalangium, Antedon eschrichti, and of most species of 
Antedon and Promachocrinus; and sometimes by a groove which may extend down- 
wards to the articular rim around the opening of the central canal, as in the first radials 
of Antedon rosacea and most species of Actinometra and Pentacrinus (Pl. XXI. fig. 6d). 
In these last types the fossze are comparatively small; but in Promachocrinus and in 
most species of Antedon they occupy nearly or quite half of the articular face, as in 
Bathyerinus aldrichianus (Pl. VUla. fig. 15, rm’; Pl. VITb. fig. 5, rm). Below the 
muscular fosse, and separated from them by more or less distinct ridges, are those 
lodgmg the interarticular ligaments (Pl. VIla. fig. 15, ’; Pl. VIIb. fig. 5, and 
Pl. Vila. fig. 7, 7). They are bounded below by the transverse articular ridge, which is 
pierced by the opening of the central canal. This is usually surrounded by a more or 
less prominent rim, from which the ridges start that separate the muscular fossee from 
the ligamentous ones and from one another. All these characters are much less distinct 
in the Pentacrinidee than in the Comatulee. 
Beneath the transverse ridge, and bounded below by the curved edge of the articular 
face is a large fossa extending right across the face and lodging the dorsal elastic 
ligament (Pl. VIIa. fig. 15, ld’; Pl. VIIb. fig. 5, and Pl. VIIa. fig. 7, Jd). As a 
general rule this igament is chiefly concentrated in a small, more or less oval pit situated 
* ae 
