EUPHAUSIA LUC ENS 207 



The abdominal segments have no dorsal spines. 



The copulatory organ of the male is very similar to that of E. vallentini and E.frigida 

 but easy to distinguish from either of them (Figs. 8 and 30 a). It differs from both in 

 that the terminal process is considerably longer than the proximal : in E. vallentini and 

 E. frigida it is shorter. The end of the terminal process is bifid, the inner of the two 

 branches longer and stronger than the outer. The end of the proximal process carries 

 on its hindermost and on its forward side a membranous expansion ; the latter is smaller 

 than the former and is set a little farther back on the process (i.e. nearer its base) and 

 does not extend so far forward ; it has a striated appearance which the hindermost ex- 

 pansion has not. On the inner side of the distal end of the process, between the mem- 

 branous expansions, there is a small tooth. Before the membranous expansions there 

 springs from the outer side of the process a strong secondary process or spine which 

 appears blade-like from some angles because one edge is more heavily chitinized than 

 the other. The lateral process is strongly and sharply curved at the end and carries on 

 that curve a strong tooth of a characteristic shape. 



Males may be sexually mature at the length of 11 mm., females at 12 mm. — that is, 

 specimens of these lengths have been seen carrying ripe spermatophores. Both sexes 

 may, exceptionally, reach the length of 18 mm. The vast majority of the specimens 

 found were between 10 and 15 mm. long. 



E. hicens is the smallest of the species described in this paper. None of its larval 

 stages has been described. 



Remarks. I cannot agree with Hansen (191 1, pp. 14-15) that the two specimens 

 described by Illig (1908 a, pp. 54-5, figs, i, 2) as Thysanopoda megalops, sp.nov., 

 cancelled by him later in the same year (Illig, 1908 b, p. 463), were possibly E. lucetis. 

 Both were 20 mm. long, longer than any E. lucens I have seen ; they had, according to 

 Illig, no denticles on the under edge of the carapace and no lappet on the basal segment 

 of the antennular peduncle ; they had a median spine above the base of the eye-stalks ; 

 and they differed in other ways from E. hicens. 



Colosi (1917, pp. 186-7, pl- xiv, figs. 9 and 10) described the new species E. uncinata 

 from one male found among seventy specimens of E. lucens. It differed from E. hicens 

 in only one way: the median lobe of the copulatory organ of the male had at the base of 

 the lateral process an additional and smaller process, uncinate in shape with a strong 

 secondary tooth near its apex. Tattersall (1924, p. 20) thought it reasonable to regard 

 this as an abnormal male of E. lucens. I am satisfied that it is of this species and that 

 what Colosi saw and drew as an additional process was not that but the lateral pro- 

 cess of the succeeding moult, displaced perhaps in fixation. I have seen the same 

 thing in E. lucens itself (Fig. 90) and in E. spinifera (Fig. 286 i), and there was no 

 doubt that the additional process was within the tissues of the median lobe ; its apex 

 lay below or within the base of the lateral process. The appearance does not, how- 

 ever, seem to be a common one in the species of Euphausia described in this report. 

 I have noticed it often in Thysanoessa vidua, in which it is not uncommon to see the 

 rudiments of the three larger processes, the terminal, the proximal and the lateral, 



