8S MS. P. H. CARPENTER ON THE GENUS ACTINOMETRA. 



which the interradial furrow is situated. The outer lips of these apertures, like the inner 

 ones (PI. V. fig-. 10), are raised and applied to the similarly inflected edges of the five 

 spout-like interradial processes of the rosette, so that the furrow lying hetween the aper- 

 tures becomes converted into a complete canal. A bristle, therefore, which lies in the course 

 of this furrow (PI. V. figs. 12, 13, II) is concealed by the interradial process (o) of the 

 rosette. The dorsal end of the latter unites with the margins of the notch described above 

 at the central end of the dorsal interradial furrow, so as to produce a roundish interradial 

 opening on the dorsal aspect of the pentagonal base, through which the bristle passed 

 along the axial interradial furrow emerges from its concealment beneath the interradial 

 process of the rosette (figs. 12, 13, II). The manner in which these openings are closed 

 in the natural condition by the central ends of the rays of the basal star will be best 

 described further on. 



(§ 60) In the condition and relative inclination of their dorsal and internal faces, the 

 first radials of Act. robusta are more like those of Ant. rosacea than those of any other 

 of tin- various Actinometree which I have examined. In Ant. rosacea the ventral sm'face 

 of the eentrodorsal piece (PL IV. fig. 15) is almost flat, as the five radial areas into which 

 it is divided lie nearly in a horizontal plane; and I he corresponding dorsal surfaces of 

 the five first radials are likewise horizontal, and form an angle of but little more than 90° 

 with the internal faces (PI. IV. fig. 12 b, c). In Act. robusta this angle becomes more 

 obtuse, so that the dorsal surfaces of the radials are somewhat inclined to the horizontal 

 plane (PL V. figs. 10, 13) ; and, in correspondence with this, the radial areas on the 

 ventral surface of the eentrodorsal (fig. 11, r.ar.) have a slight downward and outward 

 slope between their central and peripheral margins, so that the whole surface rises very 

 gradually from the circumference towards the centre. 



This is also the case in Act. Solaris, in which the dorsal surface of the radial pentagon 

 slopes slightly downwards from its margin towards the opening of the central vacuity 

 in which the rosette is situated (PL V. fig. 3), so as to correspond with the gradual eleva- 

 tion between the circumference and centre of the ventral surface of the eentrodorsal on 

 which it rests (fig. 2). 



Act. Solaris also agrees with Act. robusta in the fact that the sides of the dorsal inter- 

 radial furrow (fig. 3, a.i.f) which is produced by the truncation of the adjacent supero- 

 lateral edges of two contiguous radials are simple and straight, and not raised into 

 leaf-like folds, as in Act. pectinata (fig. 9 b) and Act. polymorpha (PL VI. figs. 9, 13, 21 ; 

 PL VII. figs. 1 d, 1 d, b.g). 



In Act. Solaris there are none of the apertures which occur in Ant. rosacea and Act. 

 robusta, by which the axial radial canals open upon the dorsal surface of the radial 

 pentagon (PL IV. fig. 10, and PL V. fig. 12, Q). We have already seen (sect. 57) that they 

 may be absent in Ant. celtica (PL IV. fig. 3) ; and their absence in Act. Solaris is due to 

 the same cause as in this case, viz. to the want of a central notch on the inner margin 

 of the dorsal face of each first radial, and to the obliteration of the lumen of each canal 

 by the ingrowth of calcareous tissue from its sides. 



In the closely allied Act. pectinata, however, these openings may be present (and not 

 improbably also in other specimens of Act. Solaris than the one which I have examined); 



