MR. P. H. CARPENTER OX THE GENUS ACTINOMETRA. 77 



figs. 12 a, 14, fj), and they only appear on the ventral aspect of the radial pentagon 

 because of the inclination of these faces to the vertical axis of the calyx. They do not 

 appear to exist in Ant. celtica (PI. IV. figs. 4, 6, 8), in which the radial muscles are 

 far larger than in Ant. rosacea, so that the vertical lamellae to which they are attached 

 attain a ninch greater size. These are placed at such an angle to the dorsal portions of the 

 distal faces of the ra dials that they stand up nearly vertically, and form the outer wall 

 of the central funnel-shaped space (fig. 4, F) which leads downwards into the cavity of 

 the centrodorsal piece. Its pentagonal rim is formed, as in Ant. rosacea (fig. 17), hy 

 their superior margins, two of which, belonging to contiguous radials, bound each of the 

 five ventral interradial furrows (v.i.f) which mark the angles of the pentagon. In the 

 centre of each of the five sides of this pentagonal rim is a deep notch (fig. 6, f 2 ) ; but it 

 does not descend on to the distal face of the corresponding radial so as to form an inter- 

 muscular furrow bounded by the median descending margins of the muscular fossa?, as 

 in Ant. rosacea (figs. 14, 17, /I) ; for these fossae are so large, and extend so far towards 

 the median line, that their inner margins unite and form a prominent vertical ridge 

 (figs. 4, 6, //;;), which passes below into the elevated rim around the opening of the central 

 canal (c.c). 



(§ 52) These five notches in the sides of the pentagonal rim of the central funnel of 

 the radial pentagon in Ant. celtica (PI. IV. fig. 6, f 2 ) represent the points at which in 

 Ant. rosacea the superior or central end of each intermuscular furrow (f_) passes at a 

 slight angle, due to the inclination of the distal face, into a shallow depression (figs. 12 a, 

 17, v-r.f) occupying the centre of the small ventral face of each first radial. This depression, 

 which is much better developed in Actinometra, is far more distinct in some specimens of 

 Ant. rosacea and Ant. celtica than in others, and in the dry state is barely visible. 

 When, however, the interior of the calyx is viewed from above after the visceral mass 

 has been removed, so as to lay open the circumvisceral ccelom, and expose the ventral 

 aspect of the radial pentagon, the position of the ventral radial and interradial furrows is 

 indicated by dark lines converging towards the centre (fig. 5). These are due to the fact 

 that the parietal layer of the peritoneum which lines the interior of the calyx descends 

 into these depressions, so that its pigment is here more thickly aggregated than on the 

 rest of the ventral surface. A similar slight depression lined by the pigmented peri- 

 toneum exists on the median line of the ventral face of the second and third radials and 

 of the basal brachial segments, and it lodges the dorsal portion of the cceliac canal, which, 

 in the intervals between the segments, sends down diverticula between the muscles 

 connecting them, so that its course is readily traceable by the greater intensity of the 

 pigment along the median bine of the segments and between the two muscles connecting 

 every pair (fig. 5, v.r.f). At the base of the arms the cceliac canal becomes broken up 

 by connective-tissue septa into a number of intercommunicating spaces, which open 

 freely into the general cavity of the calyx or circumvisceral ccelom. The dorsal part of 

 the canal, however, retains its primitive relation to the skeleton and muscles, and is 

 lodged in the furrows on the ventral faces of the radials (fig. 5). 



We have already seen that the inner wall of the funnel-shaped space (F) occupying the 

 centre of the radial pentagon is formed by the inclined ventral faces of the five first 



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