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



composed of nine joints. The second and third joints of the antennae are raised into 

 tubercles on the upper surface. 



Mouth Appendages. — The mandibles (PI. VIII. figs. 9, 10) as well as the maxillipedes 

 (fig. 12) are much sculptured, the under surface being raised into a number of ridges 

 separated by deep depressions as shown in the figure ; the masticatory edge, instead of 

 being comparatively straight and smooth, as in the majority of species, is denticulate, one 

 tooth on its posterior boundary being specially prominent. On the upper surface (fig. 

 10) are two spine-like processes. 



The maxilloB do not difi'er much from those of other species ; the anterior pair 

 (fig. 11) have a short basal joint, and the terminal joint is much bent. 



The maxillipedes are shown on fig. 12 of PL VIII. ; the under surface of the basal 

 portion, instead of being flat and smooth, as is ordinarily the case in Sewlis, is traversed 

 by a number of ridges, the direction and form of which are displayed in the figure ; the 

 second joint of the palp has the peculiar shape that it has in Serolis australiensis. The 

 outer margins, instead of being convex, are concave and almost parallel with the inner 

 margins ; they are traversed from end to end by a ridge, close to and quite parallel with 

 the outer margins. 



The second pair of thoracic appendages are shown on fig. 13 of PL VIII., and 

 several of the spines from the inner surface of the penultimate joint on figs. 14, 15 of the 

 same plate. The latter are very characteristic in shape — the longer spines terminate in 

 two large oval expansions traversed by longitudinal strife which converge at the proximal 

 extremity ; the anterior of the two is shorter and broader than the posterior ; but at the 

 hinder end of the joint they become much smaller and nearly equal in size and similar 

 in shape ; between the two wing-like processes the axis of the spine is continued into a 

 thicker cylindrical tapering extremity which reaches a trifle beyond the level of the 

 posterior wing-like process. 



The third pair are in the male modified in the ordinary way (PL VIII. fig. 16). 

 The penultimate joint is oval, and furnished on the inner surface with six or seven pairs 

 of cylindrical spines, the axis of which is prolonged into a short filiform process. The 

 first joint, as in the succeeding ambulatory liml), has a row of fine branched haii-s on the 

 inner side. 



The remaining thoracic appendages are stout and strong, and furnished with serrated 

 spines, especially upon the outer surface ; the second joint has invariably a single slender 

 spine springing from al)out the middle of the inner surface; the thml, fourth, and fifth 

 joints increase progressively in size, the fifth joint being nearly or quite as long as the 

 second, though narrower. 



The three Jirst ahdominal appendages have no inner angle bearing hairs upon the 

 basal joint. 



The suture which traverses the exopodite of the operculum is at right angles 



