SYSTEMATIC REPORT >4S 



The only objection to this suggestion is that Hansen's specimen measured 9 mm. and ' the marsupial 

 lamellae were scarcely half-developed '. In the Discovery collection an apparently adult female with 

 large, well-developed lamellae measured only 9-8 mm. and this increase in size is small to be associated 

 with such considerable changes in the armature of the tail fan. However, it is possible that Hansen's 

 specimen did have spines arming the inner margin of the endopod of the uropod. As the whole form 

 of these specimens, the shape and proportions of the anterior end of the body and appendages, and 

 of the tail fan agree closely with Hansen's description of M. crassa and, furthermore, they come from 

 the same locality, I feel justified in referring them to that species. 



The male genital organ in the largest male is not unusually long and extends forward only to the 

 region of the third thoracic somite. 



Distribution. The species is only known from the north and west of the Falkland Is. and, apart 

 from the Discovery material, has not been recorded since it was first discovered. Its occurrence 

 round the South Sandwich Islands, if my diagnosis is correct, considerably extends its range to the 



southward. 



Mysidetes brachylepis Tattersall, 1923 



1923 Mysidetes brachylepis Tattersall, p. 288, figs. 



Occurrence : 



St. 148. 9. i. 27 (day). Off South Georgia, 132-148 m. 1 <$, 17 mm., not fully adult. 

 St. 172. 26. ii. 27 (day). Off Deception I., South Shetlands, 525 m., 1 adult S, 20 mm. 

 St. WS 212. 30. v. 28 (day). North of Falkland Is., 242-249 m., 1 imm. ?, 13-8 mm. 



Remarks. This species was founded on a single adult female captured by 'Terra Nova' at the 

 mouth of McMurdo Sound in 457 m. The Discovery specimens conform closely to the type. The 

 genital organ differs considerably in the two male specimens at my disposal. In the larger specimen of 

 20 mm., the antennular brushes are very well developed and the genital organs are long, running 

 forward parallel to one another in the mid-ventral line as far as the level of the third thoracic somite, 

 then diverging and curving outward to beyond the level of the mouth. They are not swollen distally, 

 but bear the usual single seta at the apex. In the smaller male of 17 mm. the antennular brushes are 

 not so densely hirsute and the genital organs are much shorter, extending forward only as far as the 

 level of the fifth thoracic somite. There is no distal curve, but their distal ends are expanded and 

 spatulate. In all other respects this specimen agrees so closely with the others and with the type, 

 that I am sure that it belongs to the same species, but I am unable to say whether the differences 

 which I have mentioned are due to age or are traumatic. The armature of the telson and uropods 

 conforms exactly to the type except in one detail. The single large spine arming each apical lobe in 

 the Discovery specimens is flanked on its inner side by a smaller spine, about half as long as the large 

 spine, but this is not present in the type. These spines are fragile and the two are only present in two 

 apical lobes among my specimens, though the indentations marking their point of origin can be seen. 

 Tattersall mentioned that his specimen was much mutilated; possibly it had two spines at each apex, 

 but the inner one had been lost. 



Distribution. The type was taken in the Ross Sea area and the Discovery captures indicate a wide, 

 possibly circumpolar, range for this species. 



Mysidetes microps sp.n. 



Occurrence: ^ &• i 



St. 39. 25. iii. 26 (day). East Cumberland Bay, South Georgia, 179-235 m., 1 imm. $, 12-8 mm. 

 St. 45. 6. iv. 26 (day). Mouth of Cumberland Bay, 238-270 m., 5 SS, 9 ??• 



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