REPORT ON THE OPHIUROIDEA. 163 



Tentacle pores very large ; those of the second mouth tentacles set in a socket, much 

 like the rest. 



This genus is of rather doubtful position. While its general structure seems to place 

 it here, the situation of the arm spines would almost bring it in the first great group. 



Ophiocymhium cavei'nosmn, Lym. (PI. XXVII. figs. 1-3). 



OphiocpnMum cavernosum, Lym., Anniv. Mem. Bost. Soc. Nat. Hist., p. 7, 1880. 



Four arm spines. Two or three disk scales in the length of 1 mm. Side mouth 

 shields small and not meetino- within. 



(Type specimen from Station 157.) Diameter of disk 7'5 mm. Arms broken, but 

 apparently about three times the diameter of the disk. Width of arm, without spines, 

 1 "2 mm. At apex of mouth angle is a boss-like jaw plate bearing a cluster of four or 

 five short, blunt, irregularly placed spines, which correspond to teeth and tooth papillas ; 

 inside these, and along the margin of the wide jaws, on either side, is a close line of 

 three or four flat, squarish mouth papillge, whereof the outermost stands on the margin 

 of the socket of the second mouth tentacle, while the opposite margin, formed by a 

 portion of the side mouth shield, bears two flattened, spine-like tentacle scales. Mouth 

 shields small and of a rounded heart shape ; length to breadth, 1:1. Side mouth shields 

 small, wide without, but narrow and not meeting within. First under arm plate pretty 

 large and wide, three sided, with an angle inward. Those beyond are shaped like an 

 axe, with a wide, curved cutting edge, and a narrow body pointing inward. The narrow- 

 ness of the inner portion comes from the encroachment of the large tentacle pores. Side 

 arm plates long but not prominent ; meeting above and below. Upper arm plates 

 small and triangular, with an angle inward. Disk thin and flattened, with a tender 

 skin covered by very thin, delicate, overlapping scales ; two or three in the length of 

 1 mm. No radial shields can be seen from the outside. There are apparently large 

 genital openings, but these are merely the creases on either side of the arm; for, in 

 reality, the under disk surface, with a very delicate scaling, is continuous over the arm, 

 and there are no genital openings in their usual position. Four delicate, sharp, some- 

 what flattened, arm spines which, though placed on the outer edge of side arm-plates, 

 have a considerable lateral motion. No tentacle scales except to the mouth tentacles. 



Colour in alcohol : disk, pale greenish-grey; arms, straw. 



Station 157.— March 3, 1874 ; east of Kerguelen Islands ; lat. 53° 55' S., long. 108° 

 35' E. ; 1950 fathoms ; diatom ooze. 



Opliioplax. 

 Opldoplax, Lym., 111. Cat. SIus. Comp. Zool., No. \'iii. part 2, 1875. 

 Teeth ; no tooth papillae. Mouth angle small and short, bearing numerous (eleven) 



