ASTEROIDEA 



97 



1. Radiaster Tizardi (Slaclen). (Fig. 55.) 

 (Syn. Mimaster Tizardi Sladen.) 

 Dorsal side rather high, sometimes much swollen and with 

 a deep furrow in the interradial mid-line. Rays short, broad, 

 tapering. Paxillae of dorsal side not arranged in regular series ; 

 each composed of ca. 15-20 short, delicate, erect spinelets. 

 Lower marginal plates somewhat larger than the upper. Oral 

 interradial areas very large, extending to the end of the rays. 



Fig. 55. — Radiaster Tizardi, oral and dorsal side. Slightly reduced. 



Adambulacral plates with 2-3 furrow spines and 15-20 slender, 

 erect spines on the outer surface. R = ca. 2 r. Grows to a 

 considerable size, at least 120 mm. R. The arms of preserved 

 specimens are often curved upwards. 



Colour in life unknown. Biology and development unknown. 



The species is known only from the British seas, from the 

 Faroe Channel ("' Triton ", " Knight Errant ") and off S.W. 

 Ireland (" Helga "), ca. 700-1500 m. Appears to be not very 

 rare in these localities. 



