244 THE VOYAGE OF H.M.S. CHALLENGER. 



Ophiobyrsa rudis, Lym. (PL XVI. figs. 18-20; PI. XLIII. figs. 16-18). 



Ophiohijrsa rwlis, Lym., Bull. Mus. Comp. Zool., vol. v., part 7, p. 131, pi. viii. figs. 198-200, 

 1878. 



Disk closely covered with sliort spines. Arms very long, tapering, and nearly 

 ■cylindrical. Six short arm spines. 



(T)'pe specimen from Station IGl.) Diameter of disk 28 mm. Length of arm 

 300 mm. Width of arm without spines 3 '5 mm. One small, short, delicately pointed 

 mouth papilla on each side of the mouth angle, and at the apex a clump of short, sharp, 

 sjiine-like papillfe, which occupy the place of teeth. Mouth shields obscured by thick 

 skin ; only their rounded outline may be distinguished. Side mouth shields and upper 

 arm plates entirely concealed by thick skin. Side arm plates project to form a thin, 

 short, flap-like spine ridge. On the upjser surface of the arm there are two longitudinal 

 rows of very short, stout spines arranged in pairs, and usually standing on tubercles. 

 Disk five-sided and rather thin, covered by a thick skin, which is closely and evenly 

 beset above and below with short, stout, smooth, sliarp spines or thorns ; they are some- 

 what longer and more numerous near the margin of the interbrachial spaces, and are 

 almost wanting just over the base of each arm. Six equal, short, blunt, flat, somewhat 

 rough arm spines, partly covered l)y skin, not so long as an arm joint, and placed on the 

 ■edge of side arm plate. Tentacles large, simple, and round. No tentacles scales. 

 Colour in alcohol, disk, yellowish-brown ; arms the same, but much lighter. 



Station 161. — April 1, 1874 ; off" entrance to Port Philip; 38 fathoms; sand. 



Ophiomyxa. 

 Ophiomijxn, Miill. & Tr., Syst. Ast., 1812. 



Disk and arms wholly covered with a thick, naked skin. No tooth pa^^illa^. Mouth 

 papillae and teeth in the form of flattened lobes, with saw-like cutting edges. Arm 

 spines stout, bulging at the base, thorny at the point, covered round the base with thick 

 skin ; near the tip of the arm, the lower arm spine has hooks along its edge. Arms 

 rounded ; arm plates imperfectly developed. No tentacle scales. Two genital openings, 

 beginuino; outside the mouth shield. 



A thick naked skin envelops the arms and disk where it is strengthened by a line of 

 marginal, overlapping scales ; minute scales are also more or less scattered on its under 

 surface. The small, irregular radial shields rest their inner end on a clump of scales, 

 after the fashion of Ophiocoma. Their outer end is articulated to a long, stout, rounded 

 genital plate,^ to whose side, at a point far inward, is attached a short genital scale, the 

 two together making a figure somewhat like a lobster claw. A row of stout scales unites 

 the mouth shield to the genital plate. The arm bones have a rather long flat top witli a 



' See Bull. Mus. Coinp. Zool., vol. iii., part 10, pi. vi. tig. 18. 



