250 DISCOVERY REPORTS 



The proximal process of E. crystallorophtas has a strong heel-hke angle on the outer side near the 

 base. Its distal part is bent inwards. From near the bend there springs a strong secondary process 

 very similar to that of E. lucens, E. vallentini and E.frigida, more heavily chitinized along its outer 

 edge than its inner, which is membranous, convex and serrate. There are, as in the other four 

 species, two membranous lobes on the end of the proximal process, a larger distal and hinder one, 

 a very small striated one on the front side which has not been described before. The latter lies, as in 

 E. superha, under the point from which the secondary process arises, not in front of it (i.e. not more 

 distally than it) as in E. lucetis, E. vallentini and E.frigida. 



The terminal process of E. superba is not similar to that of E. lucens and the others; it does not 

 have the same kind of foot-like base, and its distal end is curved and pointed, not cleft in two. The 

 lateral process has no secondary tooth. 



The terminal process of E. crystallorophias has a narrow base, but there is a sharp projection near 

 its outer side which may be homologous with the well-defined heel of the wide foot-like base of 

 E. lucens, E. vallentini and E.frigida. Its distal end is divided into two very unequal parts, of which 

 the hinder and outermost is the larger; its inner edge is, like the hinder edge of the outer lobe in 

 E.frigida to which I suppose it to correspond, finely serrate. If these parts are indeed homologous, 

 it is very interesting to find this closer relation between the neritic species of the Antarctic coasts and 

 E.frigida from the Antarctic Zone than can be found between it and E. vallentini and E. lucens from 

 the distant sub-Antarctic. 



The lateral process of E. crystallorophias, like that of E. superba, carries no secondary tooth. It is 

 longer in proportion to the length of the terminal and proximal processes than in any of the other 

 species, and it is differently shaped. It is perhaps significant that the cargo-hook shape of its end is 

 one I have seen approached in one or more of the comparatively few petasmas of E. lucens, E. 

 vallentini, E. frigida and E. superba that I have examined (Fig. 30 a 3, 6 3, c 4, </ 3). 



It is because I find that the proximal processes of E. superba and E. crystallorophias 

 are, despite differences in general appearance, made up part for part like those of 

 E. lucens, E. vallentini and E. frigida, which are very similar to one another, that I 

 regard the five species as forming a natural group. In no other species of the genus 

 does the proximal process carry a similar secondary process, or have at its distal end 

 two membranous expansions, a hinder one larger and more distal, a front one with 

 characteristic striations. The distribution of the members of the group in contiguous or 

 overlapping habitats throughout sub-Antarctic and Antarctic waters appears to me to 

 be at once a confirmation and an explanation of their relationship ; the only other species 

 occurring in these waters are E. similis which is not related to them, in the sub-Antarctic, 

 and E. longirostris and E. triacantha which are members of another clearly defined' 

 group. In other words I regard the present group as an offshoot of the genus Euphausia 

 from lower latitudes to the colder waters of the south. 



I have looked within the group for evidence of a constant trend, a progressive change 

 in structure, showing that the species form a series corresponding with the order in 

 which they occur from north to south ; showing, that is, that E. vallentini stands be- 

 tween E. lucens and E. frigida, and E. frigida between E. vallentini and E. superba, and 

 so on. Their structure does not show so ideal a series, but it does I think show that the 

 conception is a true one. 



In the first place the copulatory organs have shown the three most northerly species to be closely 

 related. Those of E. superba and E. crystallorophias, although very different from one another, have 



