180 



ECHINODERMS OF THE BRITISH ISLES 



the light, however, appearing only on irritation, chemical or 

 mechanical. 



Two species known from the British (and European) seas. 



Key to the species of Ophiopsila represented in the British seas. 

 Ann spines 7 (6-8). Radial shields distinct, small, widely separated 



1. O. aranea Forbes 



Arm spines ca. 12. Radial shields not visible externally, wholly 



covered by the scales . . . 2. O. annidosa (M. Sars) 



1. Oj^hiojysila aranea Forbes. (Fig. 101.) 



(Syn. Ophianoplus marmoreus M. Sars.) 



Radial shields distinct, not covered with scales ; they are 

 small, linear, wide apart. Dorsal plates of arms elongate oval 



Fig. 101. — Ophiopsila aranea ; part of oral side (a), of dorsal side, with 

 basal part of arm (6), and of dorsal side of arm, from the middle (c) ; 

 mouth shield of younger specimen (d). x 8. 



in proximal part of arm, farther out more rounded, broadly con- 

 tiguous. Ventral plates with a slightly concave outer edge ; they 

 are also broadly contiguous. Mouth shields rounded, with a 

 narrower outer lobe, in younger specimens simply rounded 



