51 
maxillipeds are always of considerable size, they are very like those of the males, and 
always consist of four distinct jomts. 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 Spher. Maunnopsidis the fourth joint has 
towards its apex three spiniform processes (pl. X, fig.4d), and in Mysidion abyssorum there 
are five or six somewhat similar processes along the more central part of the immer margin 
(pl. 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 maxillule, surrounding the 
base and forming the articulation of the maxilla and the maxillipeds. 
The two pairs of natatory legs of each specimen are very much alike, and they differ 
very little, comparatively, in the various species. Each leg consists of a good-sized peduncle, 
which is particularly broad in Stenothocheres egregius (pl. 1, fig. 11, m and n), somewhat nar- 
rower, or rather narrow, in the other species (see particularly pl. VIL, 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 sete on its outer margin, two very long 
plumose setze on its terminal margin; on the inner margin it has either two very long 
plumose set (pl. IX, fig. 3k) or one of this kind and one much shorter, naked seta (pl. I, 
fig. 11). 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 sete, its terminal margin two, and its inner 
margin two exceedingly long plumose setz, 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 sets on its inner margin, and in both pair of legs two similar sete 
on its terminal margin (all these sete 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: Stenothocheres, Spheronella and Choniostoma. Eyen if an examination of more 
species should show greater variety in the number of sete, such differences are not at all 
likely to be considerable, and furthermore, it is in most cases exceedingly difficult to count 
the setze 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 (pl. I, fig. 11, m‘ and n’). 
7* 
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