98 MR. P. II. CARPENTER ON THE GENUS ACTINOMETRA. 



spout-like radial processes of the rosette ; for each of these is a composite structure, 

 formed by the apposition of two of the small curved lateral processes of contiguous basals 

 (PL VI. rig-. 22, p'). This is seen in PI. VI. rigs. 6, 18, 19, particularly in the last two ; for 

 the union of the adjacent lateral processes (//) of the two contiguous basals which are 

 there represented, is seen to be incomplete, so that a slight fissure is visible along the 

 median line of the dorsal surface of the composite radial process (fig. 19, p). The peri- 

 pheral end of this radial process is united to those of the interradial processes (o) at its 

 sides by the bars of the basal bridge (b.b). Their central ends arc also united around the 

 opening of the rosette (PI. VI. figs. 4, 19, 24, II) ; but their median portions are separated 

 by the two apertures (a? 2 , y x ) by which the two adjacent secondary basal cords ( X>, li) pass 

 out under the bars of the basal bridge, to enter the two openings of the central canal on 

 either side of the axial radial furrow on the internal face of the first radial (PL V. 

 figs. 9 c, 10 ; PL VII. figs. 1 a, 4 a, a/, y), with the inflected inner edges of which the 

 radial spout-like process (p) unites. 



The openings (% u y._) by which the other branches (X u Y 2 ) of the two primary basal 

 cords pass outwards to reach the central canals of the other two radials corresponding to 

 these two basals are best seen in a dorsal view as shown in PL VI. fig. 19. This also 

 shows the two outer lateral processes (//) of these united basals, which would naturally 

 unite with those of the two next contiguous basals, one on each side, to form two more 

 radial spout-like processes. 



(§ G7) The tertiary elements which form the rays of the basal star vary very con- 

 siderably in their shape and in the completeness with which they are developed, just as 

 do the interradial furrows on the dorsal surface of the radial pentagon in which they lie. 

 In Act. Solaris (PL V. fig. 3, d.i.f) these have no curved folds at their sides, and the rays 

 of the basal star (*S') are only imperfectly calcified rods, long and narrow, like the basal 

 grooves on the ventral surface of the centrodorsal piece into which they are received 

 (PL V. fig. 2, b.g). In Act. pectinata, however, although the basal grooves are long and 

 narrow as in Act. Solaris (PL V. fig. 7), yet the dorsal interradial furrows are widened by 

 the presence of large curved basal folds at their sides (fig. 9 b, b.f) ; and in correspond- 

 ence with these the tertiary basal elements (fig. 8, S) are much wider, and also far 

 more perfectly calcified (being solid throughout), than is the case in Act. Solaris. 



In Act. robusta the central ends of these basal rays are wide and stout, and com- 

 pletely calcified as in Act. pectinata ; but their peripheral ends are much thinner, and 

 consist of a simple curved plate, which forms a sort of bridge over the dorsal interradial 

 furrow (PL V. fig. 12, S), the borders of which are straight, as in Act. Solaris (fig. 3, d.i.f), 

 and not marked by any lateral folds. The basal grooves on the ventral surface of the 

 centrodorsal piece are also simple and nearly parallel-sided (fig. 14, b.g). 



In Act. polymorpha and its varieties the condition of the basal star varies extremely, 

 like that of the basal folds and basal grooves, the development and shape of which 

 exhibit a very close correspondence with the appearance of the rays of the basal star. 



Thus, in that specimen of the type of Act. polymorpha in which the basal grooves are 

 narrow and parallel-sided, and all terminate well within the margin of the centrodorsal 

 piece (PL VI. fig. 3, b.[/), Avhile no basal folds are present at the sides of the dorsal inter- 



