UN CRUSTACEA BKUUGHT BY DU WILLEV FROM THE SOUTH SEAS. 627 



Gnathia aureola, n. sp. 

 Plates LXVIa and LXXIV e. 



The inconvenience must be admitted of publishing a new species, of whicli the 

 fully developed form is not known in either sex. But in the present instance Dr 

 Wiiley took special pains to preserve an exact record of the colouring in life, and, as 

 this is rather remarkable, it would be a pity to leave it associated with an unnamed 

 larva. For future use it may be well to recall the peoiliarity on which Hesse several 

 times emphatically insists, that syjccies of Gnathia parasitic on fish do not tvssume the 

 sexual forms while on tiie fish, but that, when removed from their host, if kept in 

 sea-water, they sooner oi' later do assume these forms. Hesse's own experience was 

 that the larger or full-grown larvae moulted almost immediately after removal. At 

 the same time he warns the experimenter that these little captives have a surprising 

 agility and are sui'e to escape unless special precautions are taken. 



In general appearance the present form differs little from the corresponding stage 

 of Gnathia maxillans, the small, delicate peraeopods forming an absurd contrast to the 

 massive fifth and sixth segments of the peraeon which offer considerable resistance to 

 the impact of a penknife and cut like a piece of hard cheese. 



The first antennae have the third joint considerably longer than the fiist and 

 second combined, those two being together about as long as the slender flagellum, 

 in which the second joint is longer than the first plus the third and fourth, the 

 second to the fourth carrpng sensory filaments. In the second antennae the last juint 

 of the peduncle is as long as the two preceding combined, but a little shorter than 

 the slender 7-jointed flagellum. 



Over the mandibles lies a broadly triangular piece, distall}' deeply emarginate, 

 with a narrowly oval central process between the rounded corners of the emargination. 

 This I sui)pi)se to represent the epi.stome and upper lip. 



The mandibles have about nine microscopic teeth on the incurved narrow apex, 

 the iiarniw portion being longer than the broader proximal part, while in the mandibles 

 f)f Anceus maaillaris the reverse is the case. 



The first maxillae are extremely narrow, except quite at the base, with three tiny 

 teeth near the needle-pointed apex. The second maxillae are similar, but rather shorter 

 and not quite so slender. 



The maxillipeds have a tolerably even breadth till near the aj)ex, the distal lobe 

 being beset with setules and apically carrying two little teeth or spinules. 



The first gnathopods though leg-like ha\e niurh the eharaclir of mouth-organs. 

 Thi'ir hooked nails project in front on either side of the organs abovi' described. The 

 ]H iiultiuiatc joint is distinguished from the small triangular antepenultiniate, which 

 undii-rides it, by a faintly perceptible suture. The preceding joints are rather short, 

 sub('i|ual. Tile five following pairs of limbs are all very similar one to anothor, the 

 last rather the longest; the armature is very slight, its most conspicuous features 

 being a subapical spinule on the bul>;ing margin of the third joint, spinules at apices 

 of thi' thvvr following joints, which also have the straight margin microscopiailly serrate, 



W. V. 83 



