AMPHIPODA OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 229 



two-thirds as long as the propod. The third uropods have the branches equal in length 

 and rather longer than the peduncle. In other respects the specimen agrees fairly well 

 with STEBBING'S description, and the lateral lobe of the head is acutely pointed as in 

 that species. 



The form that I consider the immature male differs from the female in the second 

 gnathopods (fig. 33), which are of the same general shape, with a moderately long carpus 

 but with the propod larger and stouter, its palm more oblique and bearing three short 

 conical acute teeth, one near the base of the finger, one beyond the point on which the 

 end of the finger impinges, and one midway between these two. The third and fifth 

 perseopoda are peculiar in having the merus widely dilated so as to be fully half as 

 broad as long (see fig. 34) ; in the fourth perreopod the merus is of the usual shape. 

 Whether this expansion of the merus is a sexual character, or an individual variation 

 in the particular specimen examined, I cannot say. 



Genus JASSA. 

 Jassa falcata (Montagu). 



Cancer (Gammarus) falcatus Montagu, 1808, Trans. Linn. Soc., vol. ix. p. 100, pi. v. fig. 2. 

 Podocerus falcatus and P. validus Stebbing, 1888, p. 1132, pi. cxix., and p. 1135, pi. cxxxviii.B. 

 ingens Pfeffer, 1888, p. 131. 

 australis Haswell, 1880, p. 338, pi. xxi. fig. 8. 

 Jassa pulchella Stebbing, 1906, p. 654. 

 Chilton, 1909A, p. 647. 



goniamera Walker, 1903A, p. 61, pi. si. figs. 9S-106A. 

 wandeli Chevreux, 1906B, p. 94, figs. 54-56. 

 falcata E. W. Sexton, 1911, p. 212. 



[I have given only the chief references relating to the occurrence of this species in 

 southern seas. The very numerous references to its occurrence in the northern 

 hemisphere can be readily traced from those here given.] 



South Orkneys, Scotia Bay, Station 325, and Macdougal Bay, Station 326B. 



Several specimens of both sexes and of various ages. 

 Station 414, lat. 71 50' S., long. 23 30' W. ; vertical net, from surface to 



1000 fathoms. 15th March 1904. One specimen. 



Mrs SEXTON, who has specially studied this species, believes that there are at least 

 two different forms of the adult male. 



When I came to examine the South Orkneys specimens it became quite clear that 

 some of them were almost, if not quite, the same as the northern species, and that the 

 males belonged to what Mrs SEXTON has described as the "second form." The males 

 aTee almost exactly in the characters given of the second antenna and of the 

 gnathopods for this form ; and females of this form were also present. As there are 

 two forms known of this species in European seas, it was to be expected that, if the 

 South Orkneys species was really the same species, the " first form " would also be 

 found there. This actually proved to be the case, for two specimens from Macdougal 



(HOY. SOC. EDIN. TRANS., VOL. XLVIII., 511.) 



