ME. P. H. CARPENTER ON THE GENUS ACTINOJIETRA. 89 



for the iuucr margin of the dorsal face of each first radial exhibits a slight median notch 

 (PL V. fig. 9 b, Q'), though it is by no means so distinct as in Ant. rosacea (PI. IV. 

 figs. 12 b, 16) and Act. robusta (PL V. fig. 12). 



In this species too the ventral surface of the centrodorsal plate (PL V. fig. 7) rises very 

 perceptibly from its circumference towards its centre ; and the dorsal face of each first 

 radial is very considerably inclined to the vertical internal face, the angle between the 

 two almost reaching 135° (PL V. fig. 9 b, c). Consequently, when the radial is viewed 

 from its dorsal side, the large projecting lips of the two apertures of its central canal are 

 seen below the central or inner edge of the inclined dorsal face (fig. 9 b, x', y). These 

 are not seen in a similar view of a first radial of Ant. rosacea, in which the inclination 

 of the dorsal to the internal face is very little over 90° (PL IV. fig. 12 b, c). 



(§ Gl) In Ant. rosacea and Act. robusta the slight convexities of the dorsal surfaces 

 of the first radials fit into the correspondingly slight concavities in the centre of the 

 radial areas on the ventral surface of the centrodorsal piece (PL IV. figs. 2, 3, 15, 16 ; 

 PL V. figs. 12, 14). In Act. jjGctinata, however, these areas are occupied by median 

 depressions, increasing somewhat in depth from their peripheral to their central ends 

 (PL V. fig. 7, r.ar) ; but the dorsal faces of the first radials do not exhibit corresponding 

 ridges, for they have similar median depressions, Avhich are also deepest at their central 

 ends (PL V. fig. 9 b, c, d.r.f). 



When, therefore, the dorsal surface of the radial pentagon and the ventral surface of 

 the centrodorsal piece are in their normal state of apposition, they are separated from 

 one another along the median lines of the five radials by five cavities or radial spaces ; 

 these are largest at theii* central ends, and extend in a peripheral direction to open 

 externally by five small openings situated on the margin of the small centrodorsal 

 piece, beneath the radial pentagon which rests upon and extends considerably beyond it. 



These " radial spaces " are seen in section in PL VIII. figs. 5-8, which represent parts 

 of four sections selected out of a series that was cut through a decalcified calyx of 

 Act. ;pectinata. 



The section represented in fig. 5 was cut across the angle of two radials (A, B) near 

 the edge of the centrodorsal piece, and the open outer ends of the radial spaces are cut 

 somewhat obliquely [r.s). Pig. 6 represents a section much nearer the centre, and the 

 closed inner ends of the radial spaces are seen just beneath the lower ends of the axial 

 radial canals (a.r.c), but not communicating with them. In fig. 7 two other spaces are 

 seen, cut almost longitudinally, as the section is one from the other side of the centre, 

 through the radii, C & E, almost in the direction of their axial nervous cords {ii), beneath 

 which arc the radial spaces {r.s) between the dorsal surfaces of the first radials and the 

 ventral surface of the centrodorsal piece. Lastly, in fig. 8, which represents a section 

 still further from the centre, and cut transversely to the direction of radius D, the closed 

 central end of the corresponding radial space is seen, as in fig. 7, on the dorsal side of the 

 axial nervous cord (») ; at either side of it {s) is the expanded lower end of one of the 

 axial interradial canals seen in fig. 7 (a.i.c). 



The external medium which occupies these radial spaces between the radial pentagon 

 and the centrodorsal piece is only shut off from the dorsal portion of the cadom en- 



