233 DISCOVERY REPORTS 



of its pointed branches stronger and longer than the outer, its distal end turned out- 

 wards. A tooth-like process runs forward above the third segment from near the middle 

 of the distal margin of the second. The dorsal keel of the third segment is low (Fig. 

 23 b). 



The terga of the first and second abdominal segments are produced into very small 

 rounded projections mid-dorsally. There are strong spines from the third, fourth and 

 fifth segments; all three are compressed, but the third is more strongly compressed and 

 is stronger than the fourth and fifth. The hind-margins of the terga of the posterior 

 abdominal segments are not deeply incised as they are in E. longirostris and E. spimfera 

 (Fig. 23 c). 



The terminal process of the male copulatory organ has a wide foot-like base with a 

 high exaggerated heel, the end of it turned forwards towards the toe (Fig. 28 d). The 

 whole process from the heel to the distal end is gently curved inwards and it tapers to a 

 point. About half-way along it, measuring from the bottom of the heel, there is on the 

 inner side a short finger-like structure not projecting so as to break the line of that edge 

 of the process as seen from behind, but embedded or partly embedded in a sheath in its 

 wall (Fig. 28^2). Before it the inner edge is thick- walled, but beyond it is very thin- 

 walled, while the outer edge is thick-walled from the heel to the tip ; so that the distal 

 end of the process has a blade-like appearance, the cutting edge on the inner side. 



The proximal process curves inwards a little less than half-way along it and outwards 

 again near the end. Its proximal portion is only moderately thick. The hinder inner 

 margin of the distal end is thick-walled but the process is faintly expanded and thin- 

 walled on the outer front side, and the margin of the expansion is very finely denticulate. 

 The lateral process is hook-shaped and has no secondary spines or projections on it. 

 There is a small additional spine on the median lobe. 



Over 1080 specimens were measured apart from larval stages. The largest male was 

 41 mm. long, the largest female 40 mm., but on the whole the females were slightly 

 larger than the males. The smallest ripe male, with fully formed petasma and carrying 

 spermatophores, was 26 mm. long, though not all were examined. The smallest female 

 carrying spermatophores was 24 mm. long. 



A description of the larval stages from the second Calyptopis upwards is given on 

 pp. 277-285. 



Distribution. The stations at which E. triacantha was taken are shown in Figs. 20 

 and 22. It occurs throughout the ice-free water of the Antarctic Zone and in a narrow 

 belt of the sub-Antarctic. 



It may occur at the edge of the pack-ice but it is more frequently absent from it ; it is 

 probably very unusual to find it some way inside the pack-ice as we did at two stations 

 to the east of the South Sandwich Islands in January. Only one was found at each 

 (E.frigida was found at them too, see p. 216). At both stations the surface and deeper 

 waters were warmer than at those near them ; they were not so directly in the path of the 

 Weddell Sea Current but were in eddies of warmer water. E. triacantha is not on the 

 whole found so far south as E.frigida. The lowest surface temperature at which it was 



