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



and still on the jaw plate, are three spiniform tooth papillae. Then, from apex of mouth 

 angle, there radiate, on each side, two rows of long flattened mouth papilla?, which 

 completely hide the underlying parts ; each row has five or six papillaj, of which the 

 innermost one is spiniform, resembling a tooth papilla ; those beyond, more or less 

 spatula shaped, grow progressively larger and wider, until the outermost has almost a 

 fan shape ; all incline more or less downward and outward, so that they overlap, tUe 

 fashion. On cutting away the mouth papillae, a small mouth shield, of an irregular, 

 short diamond shape, may be seen, together with small triangular side mouth shields, 

 which nearly meet within. Length of mouth shield to breadth, "7 : '7. The jaws are 

 long, narrow, and slender, with very large sockets at their l^ase for the second pan- of 

 mouth tentacles. The first under arm plate is minute, triangular, and difficult to 

 distinguish ; the second very narrow, closely soldered with surrounding parts, and with 

 deep re-entering curves on the lateral sides ; the fourth plate is four sided, aljout as 

 broad as long, much wider without than within, and with deep re-entering curves on the 

 lateral sides ; length to breadth, "6 : "7. Side arm plates separated below, meeting 

 narrowly above, not swollen, but clean cut and flaring outward. Upper arm plates twice 

 and a half as broad as long, shaped like segments of a circle, with a clean curve outward ; 

 near tip of arm nearly as long as wide, and form a pointed curve, while the side arm 

 plates are but slightly flaring and meet above on a line as long as the upper plate. The 

 •disk was much torn (as is usually the case,) but was evidently covered alcove and below 

 with fine scales, about four in the length of 1 mm., whereof many bore minute, peg-like 

 spines. Eleven arm spines, increasing rapidly in length from the first to the ninth, then 

 diminishing ; the uj^per ones are slender, sharp, and little flattened ; the lower ones are 

 broad, flat, sharp, and shaped like a bronze sword ; lengths to that of an under arm plate, 

 •2, -3, -3, -3, -5, -7, -8, 1, 1-2, 7, 7 : 7. The basal under arm plates, as far as the fifth 

 or sixth, bear on each lateral side three long, flat, spatula-like tentacle scales, which 

 project over the pore ; for some distance beyond there are but two such scales, while a 

 third, trowel-shaped, stands on the edge of the side arm plate. One-third out on the 

 arm there remains only the large trowel-shaped scale. Colour in alcohol, pale grey. 



Station, off Tristan d'Acunlia ; 1000 fathoms. 



The peculiar twisting upward of the arms and disk of Opliiomyces is explained by the 

 absence of radial shields, a want not yet observed in any other genus. It seems, then, 

 that one function of radial shields is to keep the disk in shape, somewhat like the action 

 of the sticks of an umbrella. 



Species of Opliiomyces not herein described. 



Opliiomyces mirahilis, Lym., Bull. Mus. Comp. Zool., vol. i., part 10, p. 343, 1869. 

 Florida ; 237 to 306 fathoms. 



