138 DISCOVERY REPORTS 



Since the type of aiitarctiais was taken in the same region, these specimens may 

 reasonably be regarded as typical for the size, which is close to that of the specimen of 

 fuscus. They measure as follows: R 37 mm., r 12 mm. ; R 35 mm., r 10 mm. In general 

 appearance they are very similar to fiiscus but the groups of spinelets are smaller and 

 more closely placed (hence more numerous), while the spinelets themselves are de- 

 cidedly more delicate. They measure about 0-5 mm. in length while the pedicel of the 

 abactinal plates is 0-22-0-25 ^'^^^- high — about the same as in fuscus. The spinelets are 

 slightly clavate, the terminal half being thorny but, as the figure shows, there are no 

 radiating laminae (Fig. B, i). 



These two specimens lack differentiated inferomarginal plates. It is questionable 

 whether much reliance can be placed on this character. The actinal spinelets are less 

 robust than in fuscus and the membrane is thinner but the number of spinelets is the same.- 



The adambulacral spines have very nearly the same arrangement as in fuscus but are 

 slenderer. The furrow spine, especially, is less robust; and instead of being chisel- 

 shaped, it gradually tapers to a rather slender extremity. However, Koehler's figure of a 

 large specimen oi antarcticus from the Palmer Archipelago (1912, pi. 3, fig. 6) indicates 

 very prominent, heavy, furrow spines, as also does his figure (1920, pi. 27, fig. 8) of a 

 medium-sized example from Adelie Land (R 46 mm.). In this, the furrow spine is 

 strongly spatulate. The smaller furrow spines of the Discovery specimens are probably 

 individual variations, unless there exist definite formae with heavier and slenderer 

 spinelets. The gonads are well developed. 



Four of the specimens described and figured by Koehler (1920) were taken along the 

 Antarctic coast between 92° E and 166° E, while a fifth (191 1) came from Ross Island in 

 the south-western corner of Ross Sea, a region far removed from the type locality, the 

 Antarctic Archipelago. These specimens may ultimately prove to be closer to typical 

 fuscus than those from the type locality. 



As Koehler has shown, fully grown examples of antarcticus undergo a considerable 

 loss of the dorsal skeleton, while the muscular layer of the body wall thickens. Com- 

 parison of such specimens with the small type oi fuscus would be misleading. It is 

 probable that large examples of typical fuscus exist in Kerguelen waters, since this 

 region is well within the Antarctic zone. When these are dredged we shall know whether 

 a corresponding reduction of skeleton takes place with advancing age. 



Type locality. Probably Palmer Archipelago, near Port Lockroy. 



Distribution. Probably circumpolar. Records between 92° E and 166° E, 65° S to 

 77° 32' S (Ross Island). In the American Quadrant, along the Antarctic Archipelago. 

 Bachymetric range, 11-335 ^^ 



Perknaster densus Sladen 



(Fig. A, 3-3/; Plate VIII, figs. 1-2) 



Perknaster densus Sladen, 1889, p. 552, pi. 97, figs. 1,2; pi. 98, figs. 11, 12. Off Cumberland Bay, 

 Kerguelen, 127 fathoms. 



St. 1563. Off Marion Island, 46° 48-4' S, 37° 49-2' E, 101-106 m., i specimen. 



