250 



ECHINODERMS OF THE BRITISH ISLES 



above arms, fairly deep, containing 3-4 rudimentary dorsal 

 plates. Arms rather broad, flattened below, roof-shaped arched 

 above. Dorsal plates of arms much broader than long, with 

 outer edge straight or concave. Ventral plates very short and 

 broad, with outer edge straight and with a small peak within ; 

 beyond the disk they are triangular ; they are widely separated, 

 at most the two first contiguous. Pores in proximal part of arm 

 with several tentacle scales ; beyond the disk there are only 

 2, farther out only 1 scale. Three very small arm spines, placed at 

 about equal distances from one another, decreasing in size from 

 the lowermost upwards. Mouth shields rounded triangular ; 



1 3 



Fig. 136. — Ophiopleura horealis ; part of oral (1) and dorsal side (2), three 

 arm joints from ventral side (3). x 3. 



5-6 close set, small mouth papillae, those on the apex of jaw 

 somewhat enlarged. In large specimens there are generally 

 some supplementary series of teeth, so that these, apparently, 

 have tooth papillae. Genital slits short, not reaching to the edge 

 of disk, distinctly papillate along both edges. Colour in life red 

 or orange, sometimes bluish between the radial shields. Grows 

 to a very considerable size, up to 45 mm. diameter of disk, and 

 is one of the largest of Ophiuroids. Arms ca. five times as long 

 as the diameter of disk. 



Development unknown. Biology probably as in Ophiura. 



In British seas this magnificent species has only been found 

 in the cold area of the Faroe Channel, 60° 57' N., 4° 38' W., 

 1098 m. (" Michael Sars "). It is a purely arctic species, char- 

 acteristic of the cold area of the Norwegian Sea, distributed 

 from east Greenland to Spitzbergen, Franz Joseph Land, and 

 the Siberian Sea as far as 124° 41' E. Bathymetrical distribu- 

 tion ca. 10-1400 m. 



