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



uud pinnate at their extremity. There are generally two upon each of the smaller anterior 

 lobes and a greater number upon the posterior lobe ; in a specimen of Serolis cornuta 

 {cf. PI. 1. figs. 9,10) this pair of maxillse, like the mandibles, was asymmetrical on one 

 side ; each of the two smaller lobes had two long hairs upon its free extremity ; on the 

 side one of the smaller lobes was markedly larger than the other, and furnished with four 

 hairs instead of two. 



In Serolis convexa the second pair of maxillse differ in that all the three lobes are 

 approximately of equal size, and all bear a considerable number of hairs (PI. VI. fig. 14). 



The maxillipedes are of considerable size and entirely conceal the subjacent maxillse ; 

 they are closely approximated in the middle line ; each consists of a squarish basal portion 

 and a palp ; the basal portion is divided by a transverse suture into two, and each of 

 these is again divided by a longitudinal suture ; the proximal half or cardo articulates 

 with both the median (sphenoidal plate) and the lateral portion of the sternum. The 

 outer half of the distal half or "stipes," which is generally, though not always, completely 

 separated from the inner " lamina" by a suture, is thin and flat ; the lamina is stout, -and 

 usually furnished on the inner margin with a row of fine hairs ; the upper end invariably 

 bears two thick spines ; the palp of the maxilla, which consists of three joints, the 

 middle one the longest, is attached to the lamina about three-quarters of the way down ; 

 the second and third joints of the palp are furnished with long hairs on the iimer side 

 in all species ; the other joints of the maxillipede are sometimes smooth, sometimes 

 furnished with long hairs, according to the species. , , 



The second thoracic appendage {cf. PI. VI. fig.-^^ is modified into a prehensile organ, 

 the penultimate joint is large and swollen, and the terminal joint is recurved and lies 

 along its inner margin like the blade of a penknife when closed ; the inner margin of the 

 penultimate joint has a number of peculiarly formed spines, unlike any that are found 

 elsewhere on the body. Of these there are two kinds which regularly alternate ; one set 

 (PI. VIII. fig. 15) consist of a central stem terminating above in a knob,^ the margins are 

 beset with a number of fine branches which are fused together on each side for the 

 greater part of their length ; the other kind of spines (PI. VIII. fig. 14) which alternate 

 wdth these, and are placed slightly more on the ventral side, are long and delicate, 

 expanding above into two processes, one of which is frequently longer and somewhat 

 spoon-shaped, between these the central axis of the spine terminates in an oval knob ; the 

 shape of these hairs varies much in the different species, and will be more fully described 

 below under the several species. 



The fourth joint of this appendage, which is sometimes (Serolis tuhercidata) prolonged 

 into a forwardly directed triangular process, is always furnished with two spines, and has 

 in the males of Serolis convexa and Serolis gaudichaudii a tuft of sensory hairs (see p. 17). 



The third pair of thoracic appendages in the male (see p. 16) is modified into a 



1 Owing to an error in the plate, this is represented as a forked process. 



