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



The aiiteiinal scale (see fig. 6) projects but very slightly beyond the second joint of 

 the antennular peduncle, and exhibits an oblong-linear form, with the apex narrowly 

 rounded and the outer corner jutting out as a small but distinct dentiform projection. 

 The basal spine is very narrow and quite smooth, and the basal part of the flagellum 

 slender, with the two outer joints equal in length. 



The anterior and posterior lips (figs. 7, 8) differ but slightly in structure frcan tliose 

 of Euphausia, nor do the mandibles (fig. 9) show any characteristic feature, their 

 palp being relatively small, with the last joint oblong in form. 



The first pair of maxillae (fig. 10) are more particularly distinguished by the unusually 

 small size of the exognath, which for the rest exhibits the usual structure. 



The second pair of maxillas (fig. 11) have comparatively a slight development, with 

 the exognath almost obsolete and the terminal joint ovate. 



The general structure of the maxillipeds (fig. 12) and of the five anterior pairs 

 of legs (figs. 13-15) agrees very nearly with that in Euphaxisia. On the other hand, 

 the two last pau's exhibit very marked differences. 



The penultimate pair of legs (fig. 16), which in Euphausia are quite rudimentary, 

 arc developed precisely as the preceding pairs, exhibiting, as they do, the full number of 

 endopodal joints, together with a fully developed exopod. In the present sj)ecies, this 

 pair, however, is somewhat smaller than the preceding, having the meral joint scarcely 

 longer than the ischial, and the terminal part (three last articulations) much shorter than 

 the meral joint. 



The last pair of legs (see figs. 17, 17«) want every trace of an endopod, but have the 

 exopod in every respect normally developed. 



The gills (figs. 17, 20-25) exhibit certain well marked ditfercnces in structure as 

 compared with those in Euphausia. With the exception of the simple epipodal lobes, 

 which in this genus, as in Euphausia, are affixed to the maxillipeds (see figs. 12, 19), and, 

 in a strict sense, correspond to the true In-anchise, all of them exhibit a secondary branch, 

 springing from the main stem at the base interiorly, and backwards gradually becoming 

 more developed. On the gills belonging to the two first pairs of legs (figs. 20, 21) this 

 branch, in the specimen dissected, was c[uite sim^ile, and in appearance similar to that of 

 the gill-lobules arising from the outer edge of the curved stem. On the succeeding pair 

 (fig. 22) the branch was considerably larger, and exhibited two short lateral lobes on either 

 side. That of the fourth pair of gills (fig. 23) had three well-developed lobes on either 

 side, besides a smaller one at the base. On the fifth pair of gills (fig. 24), too, three 

 bipartite lobes have made their appearance at the base of the branch, in addition to the 

 six simple ones; and on the sixth (penultimate) pair (fig. 25) two of these basal lobes 

 had assumed a structure similar to the main stem (or outer branch), being fringed along- 

 one of the edges with a row of well-developed gill-lobules. The last pair of gills (see fig. 1 7) 

 arc much larger than any of the preceding, and consist of two principal stems pointing in 



