MR. P. H. CAEPEXTER ON THE GENUS ACTIXOMETRA. Ill 



passes round the openiug of the central canal (c.c) into a pair of lateral fossfe (//), which 

 give attachment to the large interarticular ligament connecting the second with the third 

 radial. The proximal face is not quite vertical, but slightly inclined towards the distal 

 one, so that the ventral face is not much more than an edge. When the piece is viewed 

 from the ventral side, therefore (fig. 2 c), little else is visible but the fossae for the 

 muscles (f) and interarticular ligaments (h) of the proximal face and the intermuscular 

 furrow (f) descending along its median line. 



The second radials of var. 1 are very similar to those of the type, except that, as in 

 the first radials, the muscular fossne are relatively somewhat larger. In var. 2, however, 

 they are very much smaller (PI. VII. fig. 5 a,/); and there are no vertical lamellae pro- 

 jecting from the ventral margin of the distal face (fig. 5 b), as is the case in the type. 

 The lateral fossoe (k) lodging the ligamentous substance which connects the second radials 

 with one another are somewhat more marked, as the union of the second radials in pairs 

 is more complete than in the type, though not so complete as in varieties 1, 3, and 1. 



The two latter also agree with var. 2 in the fact that the proximal and distal faces of 

 the second radials are nearly parallel, and less inclined to one another than in the type 

 and in var. 1 ; so that the fossae for the muscles and interarticular ligaments are barely 

 visible when the piece is seen from the ventral side (fig. 5 c), as there is a proper ventral 

 face. Its median line is occupied by a continuation of the furrow on the ventral surface 

 of the first radial (figs. 4 c, 5 c, v.r.f), while its lateral portions are divided up, in the 

 same way as those of the first radial, into secondary ridges and furrows. 



(§ 75) The third or axillary radial of Act. poli/morplia, which gives attachment to 

 two primary arms, presents three articular surfaces — an internal one corresponding to the 

 distal face of the second radial, and two external ones, inclined to one another, with which 

 the bases of the arms articulate. 



The proximal face (PI. VII. fig. 3 a) is precisely similar in character to the distal face 

 of the second radial, being divided, like it, by a vertical ridge into two lateral fossa3 (A) 

 which lodge the interarticular ligaments. Its articular margin, when viewed from the dorsal 

 side (fig. 3 d), is perfectly straight, and does not project in the middle as in Ant. rosacea ; 

 so that the possible amount of lateral movement between the second and third radials 

 must be extremely slight. Two vertical lamella; [y) project from the uppermost margin 

 of the internal face ; but they do not form part of the surface of articulation with the 

 second i-adial, as they are excavated into fossae on their outer side for the attachment 

 of the proximal ends of the outer muscular bundles passing between the axillary radial 

 and the lowest segments of the primary arms. The two inner muscular bundles are 

 attached to the two sides of a projecting wedge-shaped process [cl) on the external or 

 distal face, the " clavicular " of Schultze ', which occupies the angle between the two ob- 

 liquely placed articular faces for the basal arm-segments. These are of precisely the 

 same character as the external faces of the first radials (fig. 3 b), consisting, besides 

 the muscular fossae (/) just mentioned, of two others for the interarticular ligaments (A), 

 and of a large dorsal fossa {j) lodging the elastic ligament, and separated from the other 

 two by a transverse articular ridge {i) , in the centre of which is the opening of the central 

 canal (c.c). 



' Loc. cit. p. 5. 



