158 



THE VOYAGE OF H.M.S. CHALLENGER. 



Fig. 37.— Second gnathopod 

 of Stereomastis sithmi. 



The first pair of gnathopoda is short and pediform, and consist of only six joints ; 

 the coxa and basis appear to be closely impacted, but not fused together ; the ischium 

 and meros are broad and flattened, the external margin forming a continuous arch, the 

 internal exhibiting signs of an articulation between the two joints ; the carpos is pear- 

 shaped, and articulates at its smaller extremity with the external angle of the meros ; 

 it is furnished with strong, stiff hairs, all of which are fringed with short, stiff, sub- 

 conical spines ; the propodos appears to be fused with the dactylos, between which and 

 it there is no definite articulation, but at the position where it normally exists, there 

 are two large, strong, slightly curved spines on the outer surface, 

 and one similar on the inner ; the meros and ischium are similarly 

 armed, but mostly on the inner margin. 



The second pair of gnathopoda is as long again as the first, and 

 has seven joints. The coxa is short and broad, supporting a rudi- 

 mentary mastigobranchial plate (fig. 37), which is very minute, 

 long-ovate in form, and attached to the coxa by a short pedicle ; 

 it is furnished with a few short, ciliated, stunted hairs ; the basis is 

 short and closely associated, if not fused, with the ischium ; the 

 ischium is long, fiat, and slightly curved ; the meros is narrower 

 and shorter than the ischium ; the carpos is one-third the length of 

 the meros, and a little thinner ; the propodos is about the same length as the carpos, and 

 not broader ; the dactylos is sharp and styliform. The entire limb is fringed with hairs 

 of different forms : on the inner side of the propodos they are short and fur-like ; on the 



inner side of the carpos they are longer and closely set, as they 

 are on the meros, but still longer ; on the outer side of the carpos 

 ami meros they are long, and fringed with small cilia that are 

 perpendicular to the stalk ; the ischium is fringed with a few long 

 ciliated hairs on the outer side, and short, stiff ones on the inner. 



The first pair of pereiopoda carries no mastigobranchial 

 appendage and only a small podobranchia (fig. 38), but attached 

 to the coxo-pleural articulation are two very small and feeble 

 plumes, the anterior and posterior arthrobranchia, but no pleuro- 

 branchia. 



The second pair of pereiopoda has a podobranchia of tolerable 

 size, attached to a calcified pedicle, that thins out as a central rib, furnished with a 

 few hairs, but with no mastigobranchia ; two larger arthrobranchia?, and a short 

 pleurobranchia, that is attached very near to the peduncles of the arthrobranchia! 

 plumes. 



The third and fourth pairs of jitereiopoda have podobranchia! similarly formed to the 

 preceding two arthrobranchia?, and a pleurobranchia, which arc longer than those of the 



Fig. 38.— First pereiopod of 

 Stercomaslis suhmi. 



