ME. P. H. CARPENTER ON THE GENUS ACTINOMETRA. 87 



it is in the natural coudition when the rosette is in situ, encloses a dorsal extension of the 

 body-cavity or ccelom. I have seen no trace of these diverticula in any other species of 

 Comatula that I have yet examined ; but they are very large and well marked in each of 

 the five first radials in Act. robusta. 



(§ 59) The furrows which occupy the median line of the ventral and internal faces of 

 the first radials thus terminate in Act. robusta (PI. V. fig. 12) precisely as in Ant. rosacea 

 (PL IV. fig. 16), by five large openings (Q) on the dorsal aspect of the radial pentagon, 

 which are closed in the natural condition by the ventral surface of the centrodorsal plate 

 on which the radial pentagon rests. 



In Ant. rosacea the course of the slightly marked interradial farrows which pass down 

 from the ventral aspect of the radial pentagon into the peripheral portion of the central 

 calcareous network is terminated interiorly by the five triangular interradial processes of 

 the rosette ; for the apices of these processes unite with the two members of every pair of 

 contiguous radials, just between the two adjacent apertures of their central canals (PI. IV. 

 figs. 3, 7, 10, o). 



In Actinometra, however, the interradial furrows both are more marked on the ventral 

 surface of the radial pentagon, and, like the radial ones, become converted into canals, 

 terminating by five openings upon its dorsal aspect. 



In Ant. rosacea the edge which separates the lateral and dorsal faces of each first 

 radial is tolerably sharp and straight (PL IV. fig. 12 b, c); but in Act. robusta it is 

 somewhat truncated (PL V. figs. 10, 12, 13), so that when the lateral faces of two radials 

 are in apposition a deep interradial furrow appears along the line of union of their dorsal 

 surfaces (fig. 12, a.i.f). In the middle of the inner margin of the floor of this furrow is 

 a notch similar to that marking the centre of the inner margin of the dorsal face of each 

 single radial, both in this species and in Ant. rosacea (PL IV. fig. 12 b, Q'), except that 

 two radials take part in its formation instead of only one. This notch marks the con- 

 tinuation towards the dorsal surface of an interradial furrow from the ventral aspect of 

 the pentagonal base. 



The edges between the internal and lateral faces of each first radial are truncated in 

 the same way as those between the dorsal and lateral faces (PL V. figs. 10, 13). In the 

 natural condition, therefore, when the lateral faces of all the radials are in apposition 

 with one another in pairs, there are five axial interradial furrows alternating with the 

 radial ones, which occupy the median lines of the internal faces. The ventral portions of 

 these, as of the axial radial furrows, are partially bridged over by the inosculating 

 calcareous processes which extend themselves towards the ventral aspect of the rosette 

 from the internal faces of the five first radials, so that a bristle passed along their course 

 is only partially visible (PL V. fig. 13, II). 



These superior portions of the axial interradial furrows are in free communication, 

 both laterally, with the radial furrows occupying the intervals between them, and cen- 

 trally with the remaining spaces of the calcareous network, of which system these two 

 sets of furrows form the peripheral part. Interiorly, i. e. towards the dorsal surface, each 

 of these axial interradial furrows passes between the two outer lips of the adjacent aper- 

 tures (x, x') of the central canals of two contiguous radials along the line of union of 



