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



large mastigobranchial plate. The outer branch consists of two joints, the basal one, 

 which is long, narrow and sub-foliaceous, is fringed on the outer margin, and supports 

 a second joint at its extremity, the plane of which is at right angles to that of the 

 basal joint ; this second joint is long, ovate, and thickly fringed with hairs ; in its 

 position it rests as an operculum against, and covers the outer and anterior outlet 

 of the branchial chamber : the second or middle branch stands at right angles with 

 the preceding, it is as long as the first joint of the previous branch, strong, foliaceous, 

 and thickly covered with hairs : the third or inner branch is shorter and broader 

 than the preceding, it is concave inwards and convex outwards, delicately foliaceous, 

 and fringed with hairs, most abundantly on the inner margin. The mastigobranchia 

 which is directed posteriorly is as long as the first branch, it is broad, thin, and studded 

 over with numerous long hairs ; on the outer margin, near the base, is a small process 

 that may be the abortive rudiment of a branchia. 



The first pair of gnathopoda (h) is subpediform ; it consists only of six joints. The 

 first or coxal joint supports a strong process thickly fringed with hairs, which appears to 

 be an obsolete or depauperised mastigobranchial plate : the second joint or basis 

 supports an ecphysis of two joints, or rather of one joint and a multiarticulate lash 

 fringed with hairs : the third joint is probably the ischium and meros combined, and is 

 tolerably long, three times as long as the basis ; it is broader near the base than at the 

 distal extremity, where it articulates diagonally with the next joint, which I consider 

 to be the carpos ; it is narrow at the proximal and broad at the distal extremity, where 

 it is fringed both on the inner and outer side with a thick brush of hairs : the penulti- 

 mate I take to be the propodos ; it is narrower at the base than at the distal extremity, 

 where it is thickly fringed with long hairs, and in the centre is deeply excavate, and 

 articulates with the dactylos in the form of a flat ovate plate, tipped with strong hairs. 



The second pair of gnathopoda (PL VI. i) is much larger than the first, and pro- 

 portionately more slender. It is pediform, and consists of seven joints. The coxa carries 

 a well-formed mastigobranchial plate, that supports a well-formed but not long podo- 

 branchial plume ; the basis is short, and supports an ecphysis consisting of a single joint, 

 which nearly equals the ischium in length, and terminates in a multiarticulate flagellum ; 

 the ischium is three-sided, flattened, the inner and outer margins parallel, the outer 

 smooth, corresponding with the basecphysis, the upper or central is denticulate and 

 hairless, but the lower or inner is fringed with long hairs ; the meros is united with the 

 ischium by an articulation, and corresponds with it in form as well as in armature, but is 

 rather longer ; the carpos is about half the length of the meros, and articulates with 

 it at the extremity, the inner side is triangular, and has each margin fringed with 

 long hairs ; the propodos is of about the same length as the carpos, three-sided, with 

 sub-parallel margins ; each side, particularly the inner as well as the margins, is 

 covered with numerous long hairs ; the dactylos is of about the same length as the 



