ISOPODA OP THE 'LIGHTNING' AND OTHEE EXPEDITIONS. S3 



Male. Frontal outline (i. d) in form as the lower part of an escutcheon, the rostrum 

 short but acute, bent do\vnwards at the extremity, and not equalling in length one third 

 of the basal joint of the upper antennae. Ocular processes not much produced, but 

 pointed and deflexed at the extremity. Eyes conspicuous. 



Carapace and peraeon-segments (i. d) without spiny armature either on the sides or 

 ventral surface, except that the last segment of the perseon has a large spine-like pro- 

 jection on the middle of its under surface. Sides of segments emarginate, and furnished 

 with a few cilia in front of the place of attachment of the limbs. 



Pleon (i. d) with the sides of the segments ciliated, and produced downwards and 

 backwards (i. l) into small but acute points, which, however, occupy such a position 

 that they are hidden when the animal is viewed from above ; ventral surface of each 

 segment with a central spine ; last segment not much produced, scarcely equalling 

 three preceding segments combined. 



Upper antennce (i. a.s) having the basal joint three times as long as broad, both 

 margins flexuous, the outer with a cilium at half its length, and with a brush of cilia 

 at the distal termination ; second joint not half as long as the first, narrow at the base, 

 but widening distally ; third not half the length or half the breadth of the second ; 

 flagellum of thirteen articulations, every other articulation furnished with an olfactory 

 appendage on its inner margin ; secondary filament of five articulations. 



Lower antennse (i. a.i) having the peduncle equal in length to the first joint of the 

 upper pair, the first joint having a lobe at the base on its inner margin ; second bearing 

 the antennal scale, which is 3-4 times as long as wide, ciliated all round, and reaching 

 the middle of the fifth joint ; third joint very short ; fourth slightly longer ; fifth more 

 than twice the length of the fourth ; flao-ellum of seven articulations. 



First gnathopods (i. gn^ 6 ) having the basos massive, as broad as long ; hand, 

 exclusive of the thumb, as broad as long, a large tooth near the base of the inner 

 margin of the thumb, which beyond this is minutely denticulate and ciliated ; the 

 denticulations, when examined under a high power, are found to consist of lancet- 

 shaped processes, which are serrulate on the upper margin (and on both margins in the 

 female) ; the finger has similar processes, but smaller, finer, and less erect. 



Second gnathopods (l. gir) have the coxa produced forwards into a triangular, pointed, 

 and ciliated process, by the side of which is a minute two-jointed palp tipped with setag 

 (the rudimentary exopodite) ; there is also a similar palp at the base of the first 

 perseopods ; meros with a large distal spine below and a smaller distal spine on the 

 back, carpus with two spines on the front, and a spine and bunch of cilia at the distal 

 corner of the upperside ; hand with three subequal spines, the more distant rather the 

 Jarger, these spines alternate with sets of about three cilia, upper margin with two 

 spines at the lower extremity ; dactylos strong, with one and sometimes two denticles 

 on the inner edge, and two cilia on the back ; close to the base of the dactylos there is 

 a very minute flattened lancet-shaped seta, furnished with rigid cilia on the margin, 



