278 DISCOVERY REPORTS 



The smallest post-larval stages, Group A above, having lost the tergal collar of the 

 Furcilia stages and not yet having begun to develop the third abdominal spine of the 

 adult, might be very difficult to distinguish with certainty from early post-larval stages 

 of E. frigida if they w^ere taken from on or near the Antarctic convergence at a point 

 where there had been some mixing of the surface waters of the Antarctic and sub- 

 Antarctic Zones (see p. 204). 



Development of Euphausia triacantha 



The euphausian larvae described by Tattersall (1908, p. 21) as having a short blunt 

 posterior spine on the carapace and a smooth anterior margin are undoubtedly of E. 

 triaca?itha. Rustad (1930, pp. 54-7, figs. 35-7) described the first larval form of E. 

 triacantha as such, a Furcilia with four pairs of setose and one pair of non-setose pleo- 

 pods, from one specimen. In a later paper (1934, pp. 19 25, figs. 3-7) he described the 

 first, second and third Calyptopis stages from five, eighteen and six specimens re- 

 spectively, and a "Cyrtopia" with seven terminal spines on the telson (my Furcilia 

 stage IV) from one specimen. 



The stages and the numbers of each that I found are as follows : 



Calyptopis: Second ... ... ... ••• ••• ••• ••• ■•■ ••• •■■ 25 



Third 95 



Furcilia: 



Stage I. With 4 pairs of non-setose pleopods 310 



With 5 pairs of non-setose pleopods ... ... ... ... ... ... 5 



With 3 pairs of setose, 2 pairs of non-setose pleopods ... ... i 



Stage II. With 4 pairs of setose, I pair of non-setose pleopods 343 



Stage III. With 5 pairs of setose pleopods, antennal endopod unsegmented 247 



With antennal endopod segmented, 8 terminal spines on telson ... ... 2 



Stage IV. With antennal endopod segmented, 7 terminal spines on telson 136 



With antennal endopod segmented, 6 terminal spines on telson ... ... 11 



Stage V. With antennal endopod segmented, 5 terminal spines on telson 71 



With antennal endopod segmented, 4 terminal spines on telson ... ... 1 



Stage VI. With antennal endopod segmented, 3 terminal spines on telson 11 



With antennal endopod segmented, 2 terminal spines on telson ... ... 3 



Stage VII. With antennal endopod segmented, i terminal spine on telson 16 



The vast majority came from either side of the Antarctic convergence between the 

 longitudes of the South Sandwich Islands and Cape Horn. 



The larvae of E. triacantha can easily be distinguished from all other euphausian 

 larvae occurring in the same waters. 



Second Calyptopis (Fig. 38 a) 



Description based on the examination of seven specimens. Fourteen were measured and were 

 I •9-2-3 mm. long. 



The carapace is high and domed, the dome surmounted by a dorsal organ; the 

 anterior margin is gently rounded ; the lateral margins broaden out strongly behind the 



