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



The disk is covered by a thick skin which much obscures the plates. In the young 

 there are two pairs of feeble tentacles, outside the mouth ; but none in the adult. 



The disk and arms had clinging to them small polyp-like creatures, about 2 mm. 

 high, and which seemed unquestionably the Scyphistoma stage of some Medusa, like 

 Cyanea. It is not easy to guess what they were doing 12,000 feet below the surface of 

 the ocean. 



Station 15G.— February 26, 1S74 ; lat. 62° 26' S., long. 95° 44' E. ; 1975 fathoms ; 

 diatom ooze. 



Ophiopl 'inthus grisea, Lyni. (PI. XXIV. figs. 10-12). 



Ophioplinthus grisea, Lym., Bull. Mus. Comp. ZooL, voL v., part 7, p. 106, pi. ii. figs. 33, 34. 



Scaling of lower interbrachial space fine (ten or twelve in a transverse row). Very 

 small, bead-like scales on first two pairs of arm tentacles. Two or three very minute, 

 peg-like arm spines, situated low down. Arms short and narrow. 



(Type specimen from Station 156.) Diameter of disk 20 mm. Width of arm close to 

 disk, without spines, 2 mm. Mouth papillae short, thick, closely soldered together, about six 

 on each side, with two longer blunt papillae at apex of jaw. Mouth shields small, very broad 

 heart-shape, with a peak within, often cracked in two or more pieces. Side mouth shields 

 small, narrow, not meeting within, and so covered by the skin as to be seen with difficulty. 

 First under arm plate large, three-sided, with inner angle much rounded and outer 

 edge slightly curved ; second and third pentagonal, -with sharp angle inward, lateral sides 

 re-enteringly curved, outer edge shghtly rounded; those beyond are rounded diamond- 

 shape, and much broader than long. Side arm plates smooth, meeting broadly below, 

 sbghtly swollen along their outer edge. The basal upper arm plates are as wide as long, of 

 a general oval form, wider without than within, and having a deep median groove. Disk 

 covered with thin, rounded, irregular plates and scales, having six large rounded primary 

 plates, one in the centre and one to each brachial space. Eadial shields very irregular, 

 rudely triangular or quadrangular, with rounded corners, separated their entire length by 

 three or more rows of disk scales ; length to breadth 3 : 3. On the under surface of the 

 disk the scales are small and very thin ; the genital scales are long and narrow, with an 

 irregular wavy outline and often broken in three pieces. The genital opening extends 

 less than half-way to the margin. The minute blunt arm spines, of which the under one 

 is largest, stand low, on the side arm plate. The second pair of mouth tentacles issue 

 from large pores, surrounded by a rim of minute, ill-defined papillae ; the tentacles of the 

 second and third under arm plates issue in like manner from smaller pores ; beyond this 

 the small tentacle issues near the base of the under arm spine, and is covered, except at 

 base of arm, by a very small spine-hke scale. The skin of the disk and base of arms is 

 thick, and obscures the finer lines. Colour in alcohol, grey. 

 Station 156 ; 1975 fathoms. 



