108 



ECHINODERMS OF THE BRITISH ISLES 



(Fig. 63, 1). tSupra-dorsal and actino-lateral membrane very thin 

 and pellucid, the whole structure of the animal being very delicate. 

 R. =ca. 1-5-2 r. Reaches a size of ca. 8 cm. diameter. Colour in 

 life delicate rose, but varying to bluish-violet or yellowish-red. 

 An OjDhiuran has been found in the stomach of this species ; 

 otherwise nothing known of its food or biology. 



In British seas this species is known only from the Faroe 

 Channel, the cold area, 1045 m. (" Porcupine ", " Michael Sars "). 

 Otherwise distributed in the Norwegian Sea to Spitzbergen and 

 east Greenland, and to the Siberian Sea. A record of its occur- 

 rence at the Azores evidently is due to a misidentification, the 

 species being rather exclusively a cold-water form. Bathy- 

 metrical distribution ca. 15-2800 m. 



2. Hymenaster giganfeus Sldbden. (Figs. 63, 3 ; 64.) 



Body very flattened, but the rays, which are, through their 

 conspicuously spiny character, well marked off from the naked 

 interradii, have the appearance of being somewhat elevated. 

 Outline nearly pentagonal, rays only slightly produced. Paxilla3 

 with 2-3 rather robust spines, projecting through the supra- dorsal 

 membrane, which gives the dorsal surface a coarsely spiny char- 

 acter. The valves around the central opening with ca. 8 fairly 



Fig. 63. — Spine of segmental aperture (1) of Hymenaster pellucidus ; jaw 

 of H. pellucidus (2) ; and H. giganteus (3) ; (the latter after Farran). 

 1. X 16 ; 2. X 8 ; 3. probably x ca. 6 (enlargement not given by author). 



robust spines. Actino-lateral spines not joining those of neigh- 

 bouring rays in the interradial mid-line. Jaws with scarcel}^ an}^ 

 median projection, the anterior margin being nearly straight ; 

 they are thus the broadest before the middle (Fig. 63, 3). Two, 

 more rarely three, about equal sized furrow spines. The spines of 

 the segmental apertures enclosed by a large, fleshy sack of almost 

 rectangular outline ; the spine itself very broad, its outer half 

 consisting of numerous very fine, parallel rods, which gradually 



