1904.J ASELLOTA-GROUP OF CRUSTACEANS, 309 



at least generally, perhaps always, both rami, while the fifth pair 

 has never more than one ramus, in all probability the esopod. 

 In the males of the same four " families" the two anterior pairs 

 of pleopoda constittite together a kind of large operculum, which 

 consists of three sepai'ate plates coupled together ; generally this 

 operculum covers completely the three posterior pairs of pleopoda„ 

 but in an undescribed form — rather similar to lanira — from the 

 Southern Atlantic it reaches beyond the hind margin of these 

 pairs, but laterally the major portion of the exopod of the third 

 pair is left uncovered ; it may be added that this exopod is longer 

 but narrower than the corresponding endopod, and does not cover 

 half of its area. The central plate of the operculum (PI. XXI. 

 figs. 4 c% 5) is long, of various breadth, with the lateral margins 

 more or less concave ; it has a conspicuous suture along the 

 middle, and is more or less cleft at the end ; each half consists of 

 the same parts as in Stenetrmm, viz., an unjointed sympod (s.) 

 and an unjointed ramus (r.). The two sympods are very long and 

 coalesced with their inner margins ; each of them has the posterioi- 

 lateral angle produced so that a triangular more or less deep 

 incision is seen between their distal pai-ts. The ramus mentioned 

 is attached to the oblique or sinuate posterior margin of this 

 produced portion, often, as in lanira., rather well marked ofi"^ 

 from it, sometimes, as in Eurycope gigantea G. 0. S., fused 

 with it so completely that a limit between them can be traced 

 only at their distal end. The rami are not coalesced with each 

 other, but are at most united by membrane in their proximal part. 

 Each lateral part of the operculum consists of a large plate with 

 the outer margin convex, the inner nearly straight or somewhat 

 concave : this plate is the distal joint of the sympod, which has 

 the two movable rami attached to the distal part of the inner 

 margin, and contains muscles for their movement ; in lanira I 

 found, besides, a very short part which, I think, must be a 

 proximal joint of the sympod. The endopod is rather slender, 

 strongly geniculate, typically two-jointed ; the basal joint is 

 directed forwards, contains a muscle to the second joint, and at 

 least sometimes, as in Etirycojje gigantea G. 0. S. (PI. XXI.. 

 fig. 6, h.) it is divided again into two joints. The distal joint is 

 directed backwards, curved and always produced into a point ', 

 often it is long, with the distal part extremely slender ; in 

 Munnopsis typica M. Sars it is even more than half as long as 

 the whole animal, reaching far beyond the abdomen, and this 

 uncovered portion is setiform. The joint contains a pear-shaped 

 or very oblong cavity (PI. XXI. fig. 6, c), which continues intO' 

 a narrow duct (c^.) opening at the end of the joint. The 

 exopod (ea;.) is very short, two-jointed ; the distal joint is shaped 

 as a hook, the function of which is to couple the appendage with 

 the sympod of the first pair of pleopoda ; on the upper (posterioi-) 

 side of the sympod an impression and a ridge is formed for the 

 reception of this hook. The three posterior pairs of pleopoda in 

 the male are exactly as in the female. 



