51 



maxillipeds are always of considerable size, they are very like those of the males, and 

 always consist of four distinct joints. Their rather stout basal joint is nearly as long as. 

 or somewhat longer than, the three following joints together; the second and the third are 

 very slender, and their joint length is a little longer, or somewhat shorter, than the last 

 joint, which is extremely slender, almost setaceous, slightly curved and pointed. All the 

 joints are nearly always smooth and naked; in Splicer. Munnopsidis the fourth joint has 

 towards its apex three spiniform processes (pi. X, fig. 4d), and in Mysidion abyssorum there 

 are five or six somewhat similar processes along the more central part of the inner margin 

 (pi. XII, fig. 2h); the third joint at its extremity is always furnished with a spine inside, 

 the articulation of the fourth joint. 



In most figures I have carefully illustrated the sub-median skeleton, which consists 

 of lists running backward from the base of the rostrum and the maxillulae, surrounding the 

 base and forming the articulation of the maxillae and the maxillipeds. 



The two pairs of natatory legs of each specimen are very much alike, and they difl'er 

 very little, comparatively, in the various species. Each leg consists of a good-sized peduncle, 

 which is particularly broad m Stenotliocheres egregius (pi. I, fig. 11, m and n), somewhat nar- 

 rower, or rather narrow, in the other species (see particularly pi. VIII, fig. 2i); from the 

 posterior margin proceed at some distance from each other two one-jointed, about equally 

 long branches, and the outer branch, which proceeds from the end of the peduncle, is broader 

 than the inner one and rather dissimilar in outline. The outer branch of the first pair of 

 legs, as a rule, has four rather short, naked setae on its outer margin, two very long 

 plumose setae on its terminal margin; on the inner margin it has either two very long 

 plumose setae (pi. IX, fig. 3k) or one of this kind and one much shorter, naked seta (pi. I, 

 fig. 1 1). The outer branch of the second pair of legs is very like that of the first pair, but 

 its outer margin has only three shorter, simple setae, its terminal margin two, and its inner 

 margin two exceedingly long plumose setae, all four of which are longer than in the first 

 pair of legs. The inner branch of the first pair of legs has four, of the second pair three 

 very long, plumose setae on its inner margin, and in both pair of legs two similar setae 

 on its terminal margin (all these setae are longest in the second pair), whereas the 

 outer margin has only one single seta, which is either short and naked, or very long and 

 plumose. These are the results of my researches in the few species whose natatory legs 

 have been examined with special care, but it must be observed that these species belong to 

 three genera : Stenotliocheres, Sphceronella and Choniostoma. Even if an examination of more 

 species should show greater variety in the number of setae, such differences are not at all 

 likely to be considerable, and furthermore, it is in most cases exceedingly difficult to count 

 the setae accurately, as the legs are very frequently folded up or standing on edge; therefore 

 it would be all but impossible to make any practical use of the presence or absence of such 

 a seta as characteristic mark of species or genera. — The two legs belonging to each pair 

 are, as usual, united by a prominent, movable transverse band (pi. I, fig. 11, m' and n'). 



7* 



