CRUSTACEA. 
[X. [ISO PODA. 
By T. V. Hopeson, F.LS. 
(10 Plates.) 
TE collection of Isopoda 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. 
I 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, Hights. 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 less 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 Arcturide 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 Hights, which was taken close to the Antarctic Circle, just as we 
were leaving those regions, that can be considered large is Glyptonotus acutus 
VOL, V. H 
