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



Dissection shows that Liitken was right, as against Ljungman and myself, in consider- 

 ing this genus {Ophiactis clavigera) nearer Ophiacantha than Ophiactis. Except in the 

 lower interbrachial spaces, the skeleton and disk plates are more massive than in the 

 former genus and the single peristomial plates are larger, so as even to form, in some 

 cases, a closed ring round the mouth. The real generic distinction, however, is in the 

 extremely thick external skin, and the comparatively ill-developed arm spines. So 

 that its relation to Ophiacantha is about that of Ophiolipus to Ophiomusium. 



See Plate XLI. fig. 8. 



Ophiolebes scorteus, Lym. (PL XII. figs. 7-9 ; PI. XLI. fig. 8). 



Ophiolebes scorteus, Lyra., Bull. Mus. Comp. Zool., voL v., part 7, p. 158, pi. vii. figs. 196, 

 197, 1878. 



Four short blunt arm spines covered with thick skin, the upper one longest. 

 Five feeble mouth papillae to each angle. Radial shields like ridges and set with 

 grains. 



(Type specimen from Station 145.) Diameter of disk 7"5 mm. Length of arm about 

 23 mm. Width of arm close to disk, without spines, 1*5 mm. There may be seen od 

 each angle the outlines of five small mouth papillae, two widely separated on the sides, 

 and one longer and more slender at the apex, all covered by a thick skin, which, when 

 removed, shows them as long, cylindrical, and stout. The mouth shields, whose outlines 

 may be vaguely seen, are small triangular, with an angle inward and outer edge curved. 

 Side mouth shields hidden by skin, which, when removed, shows them long and narrow, 

 meeting within, and nearly or cpiite joining without, between first and second arm plates, 

 so as to form a continuous line about the mouth. First under arm plate diamond-shape ; 

 the rest are pentagonal, with an angle inward and a notch without, but are hidden by 

 thick skin. No side or upper arm plates visible, but on removing the skin, the latter are 

 seen to be small, triangular, and separated by the side plates. Disk round and arched, 

 covered by a thick skin which in the centre is irregularly wrinkled. Radial shields like 

 long narrow ridges covered with a thick skin and set with small flat grains ; the brachial 

 and interbrachial spaces have the skin more or less wrinkled, and often with a few grains ; 

 the lower interbrachial spaces have the same thick, somewhat wrinkled skin. There are 

 on the first three joints three arm spines ; beyond this there are four : they are short, 

 stout, and microscopically thorny, with blunt points, and are covered with thick skin ; 

 the upper spines being longest. No tentacle scales and apparently no tentacles 

 beyond the basal joints. Colour in alcohol white. 



Station 145.— December 27, 1873; lat. 46° 40' S., long. 37° 50' E. ; 310 fathoms. 

 Station 147.— December 30, 1873; lat. 46° 16' S., long. 48° 27' E. ; 1600 fathoms; 

 globigerina ooze. 



