OPHIUROIDEA 239 



larva of this species. With regard to growth it appears to corre- 

 spond to 0. texturata. 



A pecuUar parasite is found in this Ophiuroid (especially 

 common in the Trondhjem Fjord), a red, sac-shaped organism 

 of about peas size, without any special organs, but filled with 

 eggs or embryos ; to which group of animals this (as yet 

 undescribed) parasite belongs is unknown. It lives in the 

 genital organs of the brittle-star ; by and by, as the parasite grows, 

 the genital organs are destroyed. 



In British seas this species is mainly confined to the Faroe 

 Channel ; it has also been recorded from the Rockall Bank and 

 from oft' Cape Clear. This latter locality is, however, problem- 

 atic, the identification of the specimen from there being doubtful 

 (Hoyle). As the species goes as far south as HeHgoland in the 

 North Sea, it may probably occur also along the British North 

 Sea coasts. It is circumpolar. At the Atlantic coast of N. 

 America it occurs to 35° N., in the Pacific as far south as Japan 

 and California. Bathymetrical distribution ca. 10-3000 m. 



3. Ophiura albida Forbes. (Fig. 128, 5-6.) 

 (Syn. Ophioglypha albida (Forbes).) 



Scales of disk rather coarse ; primary plates not very con- 

 spicuous. Kadial shields usually contiguous in their outer part, 

 ca. J as long as the disk radius. Arm combs with 10-12 short 

 papillae ; inner arm combs small and indistinct. Three or four dorsal 

 plates within notch, the innermost with concave outer edge, so as 

 to be rather distinctly heart-shaped, a feature very characteristic 

 of this species. Dorsal plates of arms with convex outer edge ; 

 the dorsal side of arms not roof -shaped arched. Ventral plates 

 with convex outer edge, usually contiguous in proximal part of 

 arm, but they may be distinctly separate, also in the proximal 

 part. Only 1 tentacle scale, excepting the proximal 3-5 pore 

 pairs, which have usually 2-3 scales ; at the outer edge of the 

 pore there is a small scale, until about the middle of the arm ; 

 the proximal pores may have 2-3 scales at the outer edge ; 3 

 arm spines at equal distance from one another ; the uppermost 

 is the longest, reaches to the middle of the following lateral 

 plate. Mouth shields reach about half-way to the edge of disk ; 

 3-5 simple mouth papillae on each side of jaw. Colour in life 

 usually reddish- brown, the radial shields whitish. Reaches a 

 size of ca. 15 mm. diameter of disk ; arms ca. four times the 

 diameter of disk. 



The larva, Ophiopluteus paradoxus (Joh. Miiller) (Fig. 88, 4), 



