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



The second pair of gnathopoda (fig. 15) are much larger, and also of coarser structure. 

 They originate widely apart, at the outer posterior angles of the carapace, but are 

 suddenly bent inwards so as to meet along the greater part of their length, being more 

 or less closely applied against the ventral side of the body. The basal joint is very large, 

 more than twice as long as the remaining part, and strongly indurated, exhibiting, especi- 

 ally on the lower surface, a distinct nodulose sculpture ; it gradually expands towards the 

 distal extremity, and juts out exteriorly as a large laminar projection of a somewhat trian- 

 gular or broadly lanceolate form, fringed along the inner edge with a row of short ciliated 

 bristles. At the base this joint bears a well-developed natatory exopodite of about half 

 its length, and composed of a simple cylindrical stem and a five-jointed terminal part, 

 furnished with long natatory setae. The ischial joint, not defined in the former pair, is 

 distinctly developed, though rather short and simply cylindrical. The meral joint, on the 

 other hand, exhibits a rather peculiar form, being expanded exteriorly to a large securiform 

 projection. The carpal joint is subtriangular in shape, or produced interiorly to an 

 almost right angle bearing a few simple bristles. The propodal joint is quite narrow and 

 articulated to the outer corner of the preceding joint. The terminal joint, finally, is still 

 more narrow, linear, and together with the propodal, admits of being impinged against 

 the interior projection of the carpal joint. 



The first pair of legs (fig. 16) are constructed upon the very same type as the last 

 pair of gnathopoda, and in function would seem to be intermediate between gnathopoda 

 and true legs, their basal part being generally closely applied against the ventral side of 

 the body, whereas the terminal part is freely projecting and very mobile, so as partly at 

 least to act as true locomotory organs. They are much larger than any of the other limbs, 

 equalling in length, when fully extended, the carapace and the two first segments of the 

 trunk taken together. The coxal joint, which on the gnathopoda appears but very 

 slightly indicated, is on these limbs distinctly defined (see figs. 1, 3), but so firmly con- 

 nected with the surrounding parts as generally not to be obtained in connection with 

 the leg by dissection. The basal joint is very large and strongly indurated, being more- 

 over greatly expanded in the proximal part, and forming an obtuse angle at the middle 

 of the inner edge; whereas the distal part is narrowed, without forming any expansion 

 at the apex. The edges of this joint are quite devoid of bristles except at the ajDex, 

 where a strong cUiated seta occurs exteriorly, and a much smaller one interiorly. The 

 exopodite affixed to the base of this joint is somewhat larger than that of the last pair of 

 gnathopoda, and its basal part is a little dilated at the middle, and is also more strongly 

 indurated. The remainder or terminal part of the leg is very slender, somewhat shorter 

 than the basal, and generally exhibits a geniculate bend at the junction between the 

 carpal and propodal joints. The lengths of these two joints are nearly equal, whereas 

 the two preceding are considerably shorter and thicker. The terminal joint is a little 

 shorter and also narrower than the preceding joint, and provided at the tip with 



