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



Dr. Boas, viz., that both the exopodite and endopodite take part in the formation of this 

 peculiar apparatus. For in this species it is clearly composed of two different parts, 

 well defined from each other, the posterior part apparently representing the epipodite, 

 the anterior the exopodite. The epipodite forms an irregular, oblong, membranous plate, 

 broadest anteriorly, where it exhibits a freely projecting acute corner, and gradually 

 tapering posteriorly, its extremity forming a lanceolate flap curving anteriorly in the 

 form of a hook. To the inner face of this plate are affixed six digitiform gill-lobules 

 pointing forwards, five of which form a row along a narrow inflexed lamella proceeding 

 from the inner edge, whereas the sixth occurs at about the middle line of the plate. The 

 anterior division of the branchial apparatus, which in my opinion represents the highly 

 modified exopodite, forms an anteriorly directed narrow plate, suddenly constricted in 

 front of the middle to a narrow semicylindrical neck, and terminating in a triangular 

 expanded part, which is found protruding from beneath the pseudorostral projection. 

 The whole of this division only serves as an efferent duct for the water introduced into 

 the branchial cavity, and in the living animal probably does not partake in the 

 rhythmical movements of the epipodal division. 



The first pair of gnathopoda (fig. l,gn l ; fig. 7) are rather slender and have the ischial 

 joint distinctly defined, though very small. At the end of the large and somewhat 

 curved basal joint there occur at both edges several strong plumose setae. The carpal 

 joint is densely setose on the inner edge and considerably larger than the propodal joint, 

 which is slightly dilated at the end, where it -is densely beset with bristles. The terminal 

 joint is narrow, conical, and provided with a strong apical spine. At the base of these 

 gnathopoda in the female the usual setose lamella was distinctly developed, though the 

 setae were still very short and rudimentary. 



The second pair of gnathopoda (fig. 1, giv; fig. 7 bin) are, as usual, provided with 

 well-developed natatory exopodites, the terminal part of which is composed of eight 

 setiferous articulations. In other respects the endopodite or stem has much the same 

 appearance as that of the first pair of gnathopoda, though somewhat more elongate and 

 with the basal joint slightly tapering towards the end, and bearing along the inner edge a 

 dense series of strong plumose setae. 



The first pair of legs (fig. 8) are rather slender, and, when fully extended, about as 

 long as the whole anterior division of the body. The basal joint, occupying somewhat 

 more than one-third of the length of the leg, is strongly curved and setose along the 

 whole of the inner edge and the distal half of the outer. The three succeeding joints 

 exhibit a similar relation in length to each other as in the gnathopoda, though somewhat 

 more slender, and only sparingly beset with bristles. The two next joints, on the other 

 hand, are much more elongate, and form with each other and with the preceding joint 

 distinct geniculate bends. The penultimate or propodal joint is considerably longer than 

 the terminal, which is very narrow and linear ; both joints are furnished, especially on 



