ASTEROIDEA 185 



Those which formed nodal points of the reticulum are lobed. The originally isolated 

 platelets of the younger stage are the smallest among the dissociated elements and bear 

 paxillae of secondary size. It is probable that the plates also alter in shape with age, as 

 the lobes are less well marked in large specimens. 



In young specimens, as Koehler points out, the low paxillar groups of spinelets are 

 easily recognizable, but with age become involved in the thickening (glandular) epi- 

 dermis and lose their identity, precisely as in Perknaster. In a specimen with R 35 mm., 

 primary paxillae with upward of 12 short spinelets (see Koehler, 1920, pi. 65, fig. 4) can 

 be differentiated from smaller and lower groups of 2-4 spinelets. The primary groups 

 are elements of the continuous reticulum, while the others stand on the independent, 

 secondary, platelets. In very small specimens the secondaries are few in number, and 

 the meshes of the reticulum are naturally smaller in proportion to the size of the en- 

 closing plates. 



The papulae are fairly large, not closely placed, and occur all over the abactinal surface. 



The dorsoventral interradial, calcareous pillar is slender, flexible, and the upper end 

 joins the abactinal surface about one-third r from interbrachial angle. A narrow 

 membranous septem (of which it is a part) impinges on the stomach, but between pillar 

 and interbrachium there is no septum. 



Gonads open dorsally about half way between upper end of calcareous pillar and 

 margin. In a specimen with R 78 mm. the large eggs are fully formed (i April 1926, 



St. 42). 



The actinal floor of both disk and rays is covered with a conspicuous sheet of muscle, 

 which is continuous with a thinner dorsal layer. In the rays the actinal portion appears 

 to be homologous with the marginal muscle bundle of Myoraster. Its coelomic face is 

 crossed by oblique ridges of tissue, in part muscular as in Myoraster, which pass between 

 the lower ends of the ambulacral plates. As dissepiments these die out on the side of 

 ray but their muscular elements appear to be continuous with the branched dorsal 

 system which overlies (as seen from coelom) the continuous thin sheet. The marginal 

 muscle is not obviously differentiated from the ventral (longitudinal) sheet as in 



Myoraster. 



The rays of Cuenotaster are very flexible and are sometimes coiled ventrally. It seems 

 obvious that this special ventral sheet of muscle (as well as the dorsal sheet and the dis- 

 connected dorsal plates) co-operate in some special locomotor behaviour. The animal 

 may perform undulating movements of the rays and walk on the tips of its extended 

 podia, as do some species of Liiidia. 



A specimen from St. 42 was dull greenish grey in life. 



Type locality. Admiralty Bay, King George Island, South Shetlands, 75 m^. 



Distribution. Probably circumpolar. From south of Adelaide Island (68° S) to 

 Shag Rocks, 60-391 m.,mostlyhard bottom (rocks, gravel, with mud) ; Emperor William 

 II Land to Adelie Land (89° E to 142° E, 64° 32' S to 66° 50' S), 120-700 m. 



