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



copulation ; but in no otlier Crustaceans has a similar modification of these limbs ever 

 been observed. 



As regards the structure of the mandibles themselves, and the maxillfe, we cannot of 

 course give any reliable information, since these organs do not admit of being examined 

 in the solitary specimen before us. In the female, their structure would seem, to judge 

 from the description given by the late Dr. v. Willemoes-Suhm, to be on the whole quite 

 normal. 



The maxillipeds (fig. 6) are short and thickset in structure, without any trace of the 

 usual eropodite, and want also, it would seem, the epipodite. They consist, however, of 

 the usual number of joints, which together form a strongly curved stem. The meral 

 joint is expanded interiorly to a rather large linguiform lobe, against which the outer 

 part of the maxilliped admits of being impinged. The terminal joint has the form of a 

 strong claw. 



The gnathopoda (or first pair of legs) exhibit a structure much resembling that of 

 the maxilli^jeds, though considerably larger and having the meral lol^e comparatively 

 more powerfully developed. No trace of an exopod can be detected, and the aspect 

 of these limbs is, on the whole, very dissimilar from that of other Mysidaus. In the 

 female, however, to judge from the figure given by the late Dr. v. Willemoes-Suhm, they 

 would not seem to exhibit any marked diff"erence from that usually met with in 

 Mysidans, and hence the peculiar modification both of these limbs and the maxillipeds 

 in the male must certainly stand in some relation to the act of copulation. 



Of the true legs, the two anterior pairs had been broken ofi" in the specimen examined, 

 their basal parts only, with the corresponding exopods, remaining intact. The third 

 pair (see fig. 1) exhibit a form somewhat resembling that of the gnathopoda in other 

 Mysidans, the terminal joint being not uuguiform but obtuse and densely hirsute ; and 

 the two anterior pairs may, very probably, also have exhibited a similar appearance. The 

 three remaining paii's of legs are exceedingly slender, and have the terminal part, 

 or propodal joint, not subdivided, as in most other Mysidans, and the last joint modified 

 to a distinct, though very feeble claw. 



The caudal limljs (fig. 7) are not, as usual in the males of most other Mysidaus, 

 modified to natatory organs, or pleopoda, though somewhat dissimilar in structure from 

 those in the female. They consist of a rather feeble basal part and two very unequal 

 terminal branches. The outer of these forms merely a slender cylindrical simple 

 appendage, without any armature whatever, whereas the inner branch is rather large and 

 somewhat expanded in the middle, having there an obliquely transverse series of very 

 delicate bristles, the terminal part tapering somewhat and furnished with two bunches of 

 short bristles. Any distinct articulation cannot be detected in either of the branches. 



The telson (fig. 8) is a trifle shorter than the last segment, and exhibits the form 

 of an oblongo-cpadrangular plate, being everywhere about of the same breadth and 



