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GKUSTACEA. 



IX. ISOPODA. 



By T. V. HODGSON, F.L.S. 

 (10 Plates.) 



THE collection of Isopocla brought from the Antarctic by the ' Discovery,' if not a large 

 one, possesses no small degree of interest. 



No less than twenty-five species were captured, and, with a few exceptions, these 

 are not very numerous in individuals, in fact the number of species represented by a 

 single specimen or by only two or three is unduly large. The labour involved in 

 collecting in an ice-covered area was the only serious difficulty to contend with ; of 

 course the ice sheet reduced very considerably the area of operations, open water and a 

 boat would have enormously increased the collections, and though the ' Discovery ' was 

 in Winter Quarters six weeks before the sea was effectively closed, that was a busy 

 period, and it was only at intervals that a boat's crew could be obtained. 



Another cause which operated against big collections was, in my opinion, the 

 immense numbers of the Amphipod Orchomenopsis rossi which swarmed into the traps, 

 devouring the bait, and sometimes the specimens captured, and which were themselves 

 captured ten to thirty thousand at a time. 



1 have, I think, satisfactorily proved that Serolis cornutus Studer, is merely the 

 immature form of S. trilobitoides Eights. The specimens captured by the ' Discovery ' 

 are not fully grown, but they are sufficiently so to show all the essential features 

 described by that keen observer, Eights. Dr. Studer's specimens, as well as those 

 described by Mr. Beddard, are much smaller and obviously far from mature. I do not 

 think there can be any further doubt on this question. 



No les than seven of the species described in the ' Southern Cross ' Report have 

 been found again, one in the same locality, the others with a much extended range, 

 passing, in some cases, to the opposite side of the southern hemisphere. 



The Arcturidse is another family in which specific characters become seriously 

 involved in sexual variation. The male and female of one species, Antarcturus franklini, 

 appear on PI. V. as two species, the male being there indicated under the name 

 A. australis.* It was only when all the specimens of both sexes, or as it was then 

 thought to be, both species, came to be overhauled that the error was noticed. I am 

 not aware of any such distinct case of sexual variation in other members of the genus, 

 but that it occurs to a less extent is perfectly well known. The only species other than 

 Serolis trilobitoides Eights, which was taken close to the Antarctic Circle, just as we 

 were leaving those regions, that can be considered large is Glyptonotus acutu* 



VOL. V. H 



