42 p. H. CARPENTER ON COMATUL^ TROM 



trapezoidal form ; and the opening of the central funnel which is 

 bounded by their upper edges is very narrow, their ventral surfaces 

 being very small and having a steep inward slope. Hence when 

 the calyx is viewed from above (PL Y. fig. 4 a) the greater part or 

 even the whole of these inclined external faces is visible, always 

 down to the opening of the central canal in the transverse articular 

 ridge, and sometimes even the dorsal fossae for the attachment of the 

 elastic ligament. Most Antedons have large muscle-plates, which 

 greatly increase the height of the distal faces of the radials. In most 

 species they are simply continuations of the general straight line 

 of each face ; but in a few cases {A. celtica, A. JSschrichiii, and a few 

 others) they are set on at an angle to the dorsal half of the face, and 

 stand up vertically around the opening of the central funnel. The 

 muscular fossae lodged in these plates are separated from those for 

 the attachment of the interarticular ligaments by ridges which start 

 from the raised rim around the opening of the central canal, and 

 usually run more or less obliquely outwards to meet the sides of the 

 radials. They are occasionally somewhat curved upwards, as in A. 

 JEschrichtii, and still more so in some specimens of A. hrasiliensis and 

 A, rosacea (compare fig. lA, on pi. xxxvi. of Dr. Carpenter's 

 memoir, with pi. iv. fig. 14 of my memoir on Actinometra) ; while in 

 one ' Challenger' species (from Station 212) they run almost vertically 

 upwards for some little distance, and then curve outwards, so that 

 the size of the muscular fossae above them is considerably reduced. 

 The two muscular fossae on each articular face are either separated 

 by a strong vertical ridge, which ends below in the prominent trian- 

 gular rim around the opening of the central canal, as in A. celtica, 

 A. Eschrichtii, and A. cequimarginata (PI. V. fig. 4), or more 

 rarely, A. rosacea and A. prisca (PL V. fig. 7), there is a narrow 

 intermuscular furrow, which dies out below as it approaches the 

 above-mentioned rim. 



As with the centrodorsal, so with the radials of A. hrasiliensis 

 and A. macrocnema, which differ slightly from those of other Ante- 

 dons in the following points. There is much less difference than 

 usual between the width of the upper and lower ends of the distal 

 faces, which are comparatively low, so that their long axes are hori- 

 zontal, and not vertical, as is usually the case. Consequently the 

 centre of the upper surface of the calyx (especially in A. macro- 

 cnema) is occupied by a wide funnel, the walls of which are formed 

 by the ventral surfaces of the radials. 



A. hrasiliensis has fairly large muscle-plates ; but they are quite 

 small in A. macrocnema, and the ridges separating the muscle- and 

 ligament-fossae are so slightly oblique as to be almost horizontal, 

 though their origin from the prominent and large rim of the central 

 canal is very marked. In each case, however, the general appear- 

 ance of the calyx is much more that of the Antedon than of the 

 Actinometra type. 



The centrodorsal of Actinometra (PL Y. figs. 6, 8, and fig. in 

 p. 51) is nearly always (so far as my knowledge goes) a low flattened 

 pentagonal disk with one or occasionally two rows of cirrhus- 



