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



Ophioglypha fraterna, Lym. (PL VIII. fig. 6). 



QpMoglypha fraterna, Lyru., Bull. Mus. Comp. Zool., voL v., part 7, p. 81, pi. iv. fig. 112, 

 1878. 



Five very minute, blunt arm spines, which often are rubbed off or naturally wanting. 

 Disk smooth and flat, with scales, radial shields, and mouth shields all small, and 

 obscured by skin. No arm comb. 



(Type specimen from Station 157.) Diameter of disk 23 '5 mm. Width of arm close 

 to disk 37 mm. Mouth papillae short, squarish, closely jointed together, seven or eight 

 on each side, diminishing in size inward, with three pointed and longer at apex of jaw. 

 Mouth shield small, broader than long, pentagonal, with outer edge rounded and an obtuse 

 angle within ; length to breadth 3 : 3. Side mouth shields occupying the inner angle of 

 the mouth shield, and passing beyond it ; narrower without than within, where they meet. 

 First under arm plate much broader than long, with outer edge curved ; second plate six- 

 sided, with inner laterals longest ; beyond the disk they are very broad triangular, with 

 long sharp lateral angles, an obtuse angle inward, and the outer side curved. Often the 

 lateral corners are broken off, and form separate pieces. Side arm plates broad, not 

 swollen, meeting below beyond the disk ; separated above by the upper arm plates, which 

 are broader than long, and broader without than within, having the outer edge wavy. 

 Disk high and irregularly arched, covered above and below with a thick skin, which 

 almost entirely obscures the fine disk scales and the radial shields, which may be 

 recognised as small, oval, smooth patches near the disk margin, on either side of the arm. 

 Along the edge of the genital opening is a row of minute, closely-joined, squarish papillae, 

 which extend only to the margin of the disk, the arm comb being absent. Five very 

 minute, blunt arm spines, three situated low on the edge of side arm plate and two 

 above. Often they are rubbed off, and there seem to be none. Tentacle scales of 

 the mouth tentacles similar to mouth papillae and on one side, closely continuous with 

 them ; on the first pair there are four or five scales on each side ; on the second five 

 or six on each side ; just outside the disk there are four scales on the inner side, and 

 none on the other ; and a short distance beyond there are no scales. Colour in alcohol, 

 light grey. 



It differs from Ophioglypha loveni in wanting an arm comb, and in having the disk 

 scales and radial shields obscured by skin. 



Station 157.— March 3, 1874; lat. 53° 55' S., long. 108° 35' E. ; 1950 fathoms; 

 diatom ooze. 



