424 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



The lower pinnules are long and flagellate with a serrate dorsal edge, reaching 25 

 mm. in length. They are composed of about 60 short segments, of which the basal are 

 rather broad. PI and P 2 are nearly equal, but P 3 , though of about the same length, 

 consists of fewer and larger segments, some of the lower ones being as long as or longer 

 than broad. The pinnules following are shorter and more massive with larger lower 

 segments which are nearly square in outline and overlap considerably. The middle and 

 outer pinnules are composed of more elongated, but still overlapping, segments, the 

 two lowest broader and more flattened with their apposed edges incurved. 



The disk, which is 17 mm. in diameter, and the ambulacra are naked. Sacculi 

 are abundant. 



Carpenter noted that the centrodorsal of Solanometra antarctica is somewhat more 

 conical than that of Heliometra glacialis. 



He also said that the cirri of Solanometra antarctica are much smaller than those of 

 Heliometra glacialis, even in individuals of equivalent size, not having more than 35 

 segments, a considerable proportion of which are longer than broad, while the later 

 segments project considerably more on the dorsal side than is the case in Heliometra 

 glacialis. This is especially marked in the younger cirri which are of the "small mature" 

 type, while in Heliometra glacialis those which develop in the usual way, though both 

 relatively and absolutely larger, are much more smooth-jointed. 



Rather more of the radials is visible on the exterior of the calyx in Solanometra 

 antarctica than in Heliometra glacialis, and in some instances the ends of the basal rays 

 appear between then: lower angles. 



As in Heliometra glacialis the shape of the IBri depends considerably upon that of 

 the IBr 2 . The latter are always broader than long, but vary considerably in shape 

 even in the same individual. They are almost triangular in some cases and widely 

 rhombic in others, owing to the strong backward projection which forms a sort of 

 tubercle (synarthrial tubercle) together with the very convex center of the IBr,. Car- 

 penter said that a detailed comparison of the elements of the IBr series and lower 

 brachials of Solanometra antarctica and Heliometra glacialis reveals a number of points 

 of difference between them. 



Carpenter found a variation comparable to that in the elements of the IBr series in 

 the shape of the first two brachials. The junctions of the following brachials are by 

 no means so tubercular as in the largest (Arctic) variety of Heliometra glacialis, though 

 more so than in the smaller and smoother Atlantic specimens, which are of about the 

 same size as the largest individuals of Solanometra antarctica that were obtained by the 

 Challenger. Beyond the third syzygy the brachials of Solanometra antarctica are even 

 shorter relative toj the width than they are in Heliometra glacialis, and they have a 

 very decided tendency to overlap, which is absent in that species, the arms of which 

 are unusually smooth. 



Carpenter remarked that the same may be said of the pinnule segments, especially 

 the segments of the genital pinnules nearest the calyx. In Solanometra antarctica the 

 long flagellate pinnules on the arm bases are serrate from end to end, whereas in Helio- 

 metra glacialis the middle segments are smooth with sharp edges, but nothing more. 

 In Solanometra antarctica P 3 is much more like its successor than is the case in Helio- 

 metra glacialis. Its lower segments are considerably stouter than those of P 2 , some of 

 them being as long as or longer than broad whereas in Heliometra glacialis they are 

 distinctly broader than long. In fact P 3 in Solanometra antarctica resembles P 4 in 



