ASTEROIDEA 183 



fan-wise at the dorsal end, but below is scarcely more extensive than the pillar. It does 

 not extend interradially to the margin as there is a wide free passage between the 

 adjacent rays. 



Gonads are interradial in position and empty dorsally about one-fourth r from inter- 

 brachial angle. 



In one of the large specimens from South Georgia the abactinal plates of the disk and 

 radial region of proximal half of ray have disappeared along with the basal portion and 

 in some cases all of the shaft of the paxilla. The condition is possibly pathological, as in 

 the other large example from the same station the skeleton is intact. 



The remarkable muscular system which differentiates this species from Lophaster, 

 Solaster and Crossaster is essentially a compound bundle of conspicuous size which lies 

 at the lower end of the ambulacral ossicles, against the adambulacral plates to each of 

 which a strand is attached. It therefore is very slender at the end of ray but rapidly 

 increases in size toward the base. At the distal limit of the actinal interradial area it 

 leaves the adambulacral plates and follows the ambitus as a continuous structure into the 

 adjacent ray where it follows an identical course to the tip. Over the coelomic surface of 

 the actinal interradial area a thinner sheet of muscle, composed in part of strands 

 originating in the marginal bundle, passes to the adambulacral plates. In addition, 

 narrow muscles which branch off abundantly from the conspicuous dorsal radial muscle, 

 on reaching this longitudinal muscle, become transformed into thin raised ridges which 

 cross the marginal muscle. Some of these attach themselves to the adambulacral plates, 

 while others unite and continue (as a fairly symmetrical series of ridges) between the 

 lower ends of the ambulacrals. These ridges are conspicuous across the actinal inter- 

 radial area. The fascicles of the marginal muscle (which is the pertinent innovation) are 

 therefore roughly at right angles (and somewhat covered by) these extensions of the 

 normal dorsal muscular system. 



In a specimen from St. 371 having R 120 mm. the marginal muscle measures at the 

 interradius 3-5 mm. dorso-ventrally, by 2-5 mm. horizontally— after evident shrinkage 

 from alcohol. 



I have found what is probably the equivalent of the marginal muscle, in a very rudi- 

 mentary form, in Solaster endeca. It is a very thin band, less than i mm. in width, lying 

 under the actinal extension of the dorsal muscular system, described above as traversing 

 at right angles the thick marginal muscle of Myorastcr. There is no trace of the muscle in 

 Lophaster, nor of the actinal interradial muscle sheet. 



Type locality. Between Jenny Island and Adelaide Island, bf 43' S, 70° 45' 42" W, 

 254 m., rocks and gravel. 



Dlstribution. South Georgia to Adelaide Island (67° 43' S) and off Adelie Land; 

 probably circumpolar ; 99-750 m. ; rocks and mud. 



15-; 



