238 DISCOVERY REPORTS 



There are small but constant differences between the male copulatory organs of 

 E. similis and the variety armata (Fig. 25). The proximal part of the proximal process is 

 more nearly equal in length to the terminal process in the variety armata. The processes 

 were measured in the petasmas of ten specimens of each kind — the terminal process in 

 a straight line from heel to tip, the first part of the proximal process in a straight line 

 from the outer corner of the base to the outer corner of the " shoulder ". The average of 

 ten measurements showed the length of the first part of the proximal process to be 

 76-3 per cent of that of the terminal in E. similis, 91-1 per cent of it in the var. armata. 

 (The lower and upper limits were in E. similis, 68 and 82 per cent, in the variety armata 

 81 -8 and 102-4 P^^ cent.) 



The distal half of the terminal process is bent inwards in armata, not straight as in 

 E. similis ; the foot is heavier, the instep more arched ; the shaft is shorter but thicker, 

 the curved end heavier. There are distinct differences in the structure of the projection 

 near the end and in the angle at which it projects. The first part of the proximal process 

 shows differences too : the inner margin is curved ; the outer margin is more convex and 

 is without the definite angle near the base that it has in E. similis. 



Every one of these differences is shown in Hansen's two drawings (1913, pi. iv, fig. 

 3 c and 1911, fig. 7). 



The largest male of the variety armata was 26 mm. long, the largest female 28 mm. 

 Only one female, 27 mm. long, was noted as carrying spermatophores ; I have no doubt 

 that they can be mature at a much smaller length. Some males 23 mm. long were mature. 



Distribution. The variety armata was found together with E. similis at most of our 

 stations in the warmer part of the sub-Antarctic Zone and the colder part of the sub- 

 tropical. It was absent at many of the stations at which E. similis occurred in the 

 colder sub-Antarctic (Fig. 26). Hansen (1911) records it from localities that lie either 

 in the sub-Antarctic or subtropical Zone, and from 13° S, 103° E in the Indian Ocean; 

 Zimmer (1914) and Tattersall (1924, 1925) from the subtropical or sub-Antarctic 

 Zones ; Illig (1930) from the subtropical Zone off South Africa and — the most northerly 

 record — from near Ceylon. 



Euphausia similis var. crassirostris, Hansen. 



E. similis var. crassirostris, Hansen. 1910, p. 94, pi. xiv, figs. 2 a-c; Tattersall, 1925, p. 7; Illig, 

 1930, p. 498. 



Remarks. Hansen described the variety crassirostris from three immature specimens 

 in which the frontal plate and the gastric area of the carapace was vaulted, the frontal 

 plate a little longer, the rostral process shorter than in the parent species. Although I 

 have seen over 900 E. similis and nearly 900 var. armata I have not found any specimens 

 of this kind. 



But specimens with deformed or misshapen rostra are not uncommon. In them the 

 rostrum may be : shorter than is normal ; much shorter than normal and thick and blunt ; 

 or so entirely wanting that the margin of the carapace between the post-ocular projections 

 is concave. In the more abnormal specimens the gastric area of the carapace is often 



