EUPHAUSIACEA AND MYSIDACEA—TATTERSALL. 
7 
Genus Thysanoessa Brandt. 
Thysanoessa gregaria G. 0. Bars. ? 
T. gregaria Hansen, 1911. 
T. gregaria Hansen, 1913. 
Locality. 
Oft’ Macquarie Island, 18-I9th June, 1912, 26 m. tow-net, 8 p.nn-8 a.m., sixty- 
three specimens, 4-10 mm. 
These specimens are all immature and very fragmentary. Only two specimens 
retain their long legs. In one of these specimens, 6-5 mm. in length, the fifth joint of 
the long leg is twice as long as the sixth and seventh joints combined. In the other 
specimen, 10 mm. long, the fifth joint is one and three quarter times as long as the 
combined sixth and seventh joints. In both specimens the combined length of the 
fourth and fifth segments of the abdomen is one and a quarter times the length of the 
sixth segment. Small specimens of Thysanoessa are extremely difficult to determine, 
and Hansen, who has studied this genus exhaustively admits that small T. gregaria 
are difficult to separate from small T. macrura. In the present collection there is one 
specimen of T. macrura , 10 mm. long, that is, about the size of the largest specimen of 
those I refer to, T. gregaria. It still retains its long legs, and, in these limbs, the fifth 
joint is 2-6 times as long as the combined sixth and seventh. The fourth and fifth 
segments of the abdomen are together equal to the sixth. These proportions differ 
considerably from those in the specimens I have referred to T. gregaria. 
In the figures illustrating Sars’ account of this species in the “ Challenger ” 
Report, taken presumably from specimens 18 mm. long, the fifth joint of the first leg 
is 1 -77 times as long as the combined sixth and seventh joints, and the combined fourth 
and fifth segments of the abdomen are 1 -2 times as long as the sixth. These proportions 
are in close agreement with those given above. 
I do not think the present specimens can be T. vicina Hansen, for in all that 
still retain the upper flagellum of the antennules, it is shorter than the distal two joints 
of the peduncle, whereas in T. vicina it is longer. Moreover, in T. vicina the proportions 
of the abdominal segments is about the same as in T. macrura. 
I think these specimens are correctly referred to T. gregaria, but, owing to their 
poor state of preservation, the identification must remain doubtful. 
Thysanoessa macrura G. 0. Sars. 
T. macrura Tattersall, 1908. 
T. macrura Hansen, 1911. 
T. mac'ura Hansen, 1913. 
