112 ME. P. H. CAKPENTER ON THE GENUS ACTINO.METEA. 



The median line of the veutral face (fig. 3 c) is oecupied by a ventral radial furrow 

 continuous with that on the ventral face of the first radial ; it divides into two branches, 

 one of which passes on either side of the clavicular, in order to be continued on to the 

 basal arm-segments. The proximal end of this furrow is indicated by the deep notch 

 separating the two vertical lamellae which project upwards from the proper internal 

 face (fig. 3 a, y), and through which the base of the clavicular is seen. 



In the type and in var. 1 the lateral portions of the ventral face of the third radial 

 are plain, and not sculptured ; but in varieties 2-4 they are divided up by secondary 

 ridges and furrows (fig. G c), just like the ventral faces of the first and second radials 

 (figs. 4 c, 5 c). In these varieties also there are no vertical lamelkc projecting upwards 

 from the ventral margin of the internal face (fig. 6 a), which is also the case in the ex- 

 ternal face of the second radial (PL VII. fig. 5 b), as the muscular bundles passing between 

 the fii-st and second radials, and between the third radials and basal arm-segmcuts, are 

 smaller than in the type. In var. 2 there would appear to be more power of lateral 

 movement between the second and third radials than is the case in the type; for 

 although, as in the type, there is no projection in the middle of the proximal articular 

 margin of the thh'd radial, yet the distal articular margin of the second radial shows 

 a slight indication of such a median prominence (fig. 5 d), which is absent in the type. 

 It Avould seem though, to be replaced to a certain extent by the greater thickness of 

 the vertical articular ridge {i) around the opening of the central canal, which is seen, in 

 PI. VII. fig. 2 d, to project a little beyond the level of the dorsal surface of the radial ; 

 so that when the opposed ridges of the second and third radials are in contact with 

 each other, the third may possibly have a very slight power of lateral movement upon 

 the second, though by no means so great as in Ant. rosacea, in Avhich the median pro- 

 minence on the internal articular margin of the thu'd radial is very marked. 



The second and third radials of var. 2 differ from tliose of the type of Act. ])olymorpha 

 and of aU the other varieties in the very marked convexity of their dorsal surfaces, whicli 

 renders them considerably higher than the first radials ; so that when the whole calyx is 

 viewed from the exterior, the inner circle of first radials, which are only very little con- 

 cealed by the small centrodorsal piece, seems somewhat sunk within the outer circle 

 formed by the second and tliird radials. 



This marked convexity is Avell seen in i'l. \'II. fig. 5, a, d, and fig. 0, b, d, especially 

 when these figures are compared with those of the corresponding parts in the type 

 (fig. 2, a, d, fig. 3, b, d). 



List of "\^'orks refeered to. 



1. Adams, J., " Description of some Marine Animals found on the coast of "Wales," Ti-ans. Linn. Soc. 

 vol. V. p. 7 (London, 1800). 



2. Agassiz, L., " Prodrome d'unc Monographic des Radiaircs on Echiuodermcs/' Aunalcs d. Sci. Nat. 

 2°" s^r. Zool. vii. p. 288. 



3. Agassiz, Al., " Revision of the Echini," Illust. Cat. Mus. ot Comp. Zool., No. vii. (Cambridge, U.S. 

 1872-74). 



4. Austin, T. and T., Juu., 'A Monogi-aph on Recent and Fossil Criuoidca' (Bristol, J 8 15). 



