ME. P. H. CAEPEXTEE OX THE GENUS ACTIXOMETEA. 93 



are very large, and considerably more extensive than those which lodge the interarticular 

 ligaments (I/). 



In Act. polymorpha (PI. VI. fig. 1; PI. VII. figs, lb, 4b), however, the muscular 

 fossae are very small, being best developed in var. 1 (PL VI. fig. 12,/); while the fossae 

 (h) lodging the interarticular ligaments are very extensive, and separated by the down- 

 ward continuation of the intermuscular furrow (f t ), which reaches the dorsal margin of 

 the opening of the central canal (c.c). The external faces of the first radials of varieties 

 2 (PI. VII. fig. 4 b), 3, and 4 resemble one another, but differ from the corresponding 

 faces in the type (PI. VII. fig. lb) in being somewhat higher in proportion to their 

 width, and in the fact that the fossae (j) lodging the elastic ligaments are relatively 

 smaller, not extending so far into the lower or dorsal angles of the face as is the case in 

 the type. 



(v.) The Basals. 



(§ G3) We have already seen that all the older observers regarded Comatula as devoid 

 of those five pieces resting upon the top segment of the stem to which, in the other 

 Crinoids, MuTler gave the name of " basals ; " and it was not until Dr. Carpenter l dis- 

 covered the extraordinary metamorphosis undergone by the embryonic basals of Coma- 

 tula (Antedon) rosacea and then transformation into the "rosette," that the existence 

 of basals, although internal and concealed in the adult animal, was recognized. 



The rosette of Ant. rosacea and Ant. celtlca (PL IV. figs. 3, 7, 16, H) is a peculiarly 

 shaped circular plate, occupying the dorsal half of the central cavity in the pentagonal 

 base of the calyx, which lies much nearer to the dorsal surface of the pentagonal base 

 in the latter species than in the former. 



A normal rosette consists of a disk perforated in the centre with ten rays proceeding 

 from it. Pive of these rays (PL IV. tig. 13, o') are short, triangular in form, and nearly 

 flat, and their position is interradial, as they are directed to the sutures between the five 

 radials, their apices joining the contiguous pairs of these just between the two adjacent 

 apertures (x, x') of their central canals. 



Alternating with these five interradial processes of the rosette are five radial ones 

 (fig. 13, p), each of which has parallel margins inflected on its ventral aspect in such 

 a manner as to form a groove ; while the process itself is so curved towards its dorsal 

 aspect that this groove reaches the periphery of the rosette, and then terminates 

 abruptly as if truncated. 



The inflected margins of each of these five radial or, as Dr. Carpenter has called them, 

 " spout-like " processes of the rosette are applied to the similarly inflected margins of the 

 dorsal half of the axial radial furrow, lying between the two apertures of the central 

 canal on the internal face of each first radial (fig. 12 c, x', //). In this manner a com- 

 plete radial axial canal is formed, which, as we have already seen, terminates on the 

 dorsal surface of the radial pentagon by the opening Q (fig. 10), or becomes closed 

 before it reaches the dorsal surface by the union of ingrowths developed from its walls. 



Besides this very intimate union between the peripheral portion of the rosette and the 



1 Phil Trans. 1865, pp. 744, 745. 



13* 



