REPORT ON THE CRINOIDEA. 25 



they are almost perfectly horizontal (PI. I. fig. 6a), and so give the calyx a very different 

 appearance from that of the closely allied Arctic species Antedon eschrichti (PL I. fig. 8a) ; 

 though Promachocrinus kerguelensis, another southern form, resembles Antedon eschrichti 

 in this respect (PI. I. fig. la), and the same may be said of Eudiocrinus semperi (PI. III. 

 fig. 7a). In some forms of Antedon incisa the ridges do not, as is usually the case, start 

 from the rim of the central canal, but curve upwards slightly from the median vertical 

 ridge of the articular face, and the upper pair of fossae are therefore somewhat restricted 

 (PI. II. fig. la). In Antedon disciformis (PL IV. fig. 2a) the ridges run upwards from 

 the central canal for some little distance and then curve outwards, leaving a sort of 

 furrow between them, the bottom of which is sometimes slightly raised. 1 But in most 

 species of Antedon there is a strong median ridge running down from the ventral edge of 

 the articular face towards the opening of the central canal (PL I. figs. 6a, 8a ; PL II. 

 figs. 1-5, a ; PL III. figs. 46, 5a, 6d). This is hardly traceable in Antedon carinata 

 (PL III. fis;. la), which rather resembles Antedon disciformis in having a tendency to the 

 intermuscular furrow that is so characteristic of Actinometra (PL V. figs. 1-5, b) ; while 

 in Antedon macronema the muscular fossae are so very slight, that the notch between 

 them reaches down to the upper margin of the raised rim of the central canal (PL IV. 

 figs. 3a, b), a character which rarely occurs in Actinometra. 



Thus then the radials of Antedon carinata and Antedon macronema differ from 

 those of other species of Antedon and approach those of Actinometra. There is much 

 less difference than usual between the widths of the upper and lower ends of the distal 

 faces, which are comparatively low, so that their long axes are horizontal and not vertical 

 as is usually the case (PL I. figs. 6a, 8a). The centre of the upper surface is consequently 

 occupied by a wide funnel, the walls of which are formed by the ventral surfaces of the 

 radials (PL III. fig- 1^ ; PL IV. fig. 3b). Antedon carinata has fahiy large muscle- 

 plates ; but they are quite small in Antedon macronema, and the ridges separating the 

 muscle- and ligament-fossse are so slightly oblique as to be almost horizontal, though their 

 orio-iu from the prominent and large rim of the central canal is very marked. In each 

 case, however, the general appearance of the calyx is much more that of the Antedon 

 than of the Actinometra type. The calyx of Antedon macronema further presents many 

 resemblances to that of Pentacrinus, especially in the small size of the articular faces 

 and in the large portions of the radials which appear externally (PL IV. fig. 3a). Of all 

 recent Comatulse it is the one which most closely approaches the general type of the 

 Jurassic forms of Antedon; and as it is only known to occur on the Australian Coast, 

 this is a point of considerable interest. 



The radials of Actinometra differ very largely from those of the typical Antedon. 

 Their distal faces are relatively low, and lie nearly or quite parallel to the vertical axis of 

 the calyx, while there is but little difference in width between their ujjper and their lower 



1 This is less distinctly seen in an interradial view of the calyx than in a face view of a single radial. 



(ZOOL. CHALL. EXP. — PART LX. 1888.) OoO 4 



