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



absent in Act. Solaris (PL V. fig. 3), they are well marked in the closely allied Act. pec- 

 tinata (PI. V. fig. 9 h, h.f). In two specimens of the type of Act. polymorpha (PI. VI. 

 figs. 4, 11) they are absent altogether, while in a third they are very well marked (fig. 9, 

 b.f), as also in each of the varieties, three of which are represented in PI. VI. figs. 

 13, 21, and PI. VII. fig. 4 a. In all these cases the borders of the interradial furrows 

 on the dorsal surface of the pentagonal base, which are produced by the apposition of 

 the truncated superolateral edges of every pair of contiguous radials, assume a leaf-like 

 appearance, owing to the presence of the folds at their sides. The precise shape of these 

 leaves, which is different in the type and in all the four varieties, corresponds very 

 closely with the shape of the basal grooves on the ventral surface of the centrodorsal 

 piece, with which they also correspond in position. They further resemble them in 

 the fact that they are entirely devoid of the pigment which is so abundant on the other 

 parts of the surfaces of the radial pentagon and centrodorsal piece ; so that when these 

 last are separated from one another, the dorsal interradial furrows on the pentagonal 

 base, like the basal furrows on the centrodorsal piece, stand out sharp and distinct as 

 five white leaflets on a dark-brown background. They are best marked invar. 4 (PL VI. 

 fig. 24, b.f), in which the basal folds of every pair of contiguous radials are rather widely 

 separated from each other about the middle of their length. This is also the case, 

 though to a less extent, in var. 1 (tig. 13), where, as in var. 4, the dorsal interradial 

 furrows correspond very closely in shape with the basal grooves on the centrodorsal 

 piece (fig. 15). 



This is particularly distinct in the specimen of the type represented in PI. VI. 

 figs. 8, 9, in which one of the basal grooves is much shorter than the rest, and does 

 not reach the margin of the centrodorsal piece. The basal folds at the sides of the 

 dorsal interradial furrow corresponding to this aborted groove are also imperfectly 

 developed, so that the borders of its outer end are simple and straight ; as they are 

 throughout the whole course of the furrows in Act. solans (PL V. fig. 3) and Act. robusta 

 (PL V. fig. 12). 



This last condition may also occur in the type of Act. polymorpha (PL VI. figs. 4, 11) ; 

 and in correspondence with it the basal grooves on the centrodorsal piece are simple and 

 almost parallel-sided (PL VI. figs. 3, 10, b.g), just as in Act. Solaris and Act. robusta 

 (PL V. figs. 2, 14). 



This correspondence in the appearance of the dorsal interradial furrows and basal 

 grooves which is also seen in Act. polymorpha, var. 2 (PL VI. fig. 17; PL VII. fig. 4 a), 

 is not, however, an invariable one; for in Act. pectinata the basal folds are very well 

 marked (PL V. fig. 9 b, b.f), and the dorsal interradial furrows, therefore, leaf-like in 

 appearance, as in most specimens of Act. polymorpha (PL VI. figs. 9, 13, 24). The basal 

 grooves, however, on the ventral surface of the centrodorsal piece are narrow and 

 parallel-sided (PL V. fig. 7, b.g), just as in the allied species Act. Solaris and Act. robusta 

 (PL V. figs. 2, 14). 



The external or distal faces of the first radials of Act. polymorpha differ not a little 

 from the corresponding faces in Ant. rosacea and Ant. celtica (PL IV. figs. 4, 6, 8 , 12 a, 

 11, 17) ; in which, especially in the latter, the fossse (f) for the attachment of the muscles 



