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Show 1900.] FROM THE FALKLAND ISLANDS. 553 Guerin-Meneville makes of them two separate species. But the fact is, I think, that we cannot now with any certainty determine what species Pallas had before him, and must therefore accept serratum as the type of the genus. The question now arises whether the genus ought to retain all those species which have been hitherto grouped within it on the ground of their very close external resemblance. My reply to this is that, at least in some instances, the grouping can scarcely outlast a careful comparison of the appendages in the different species. It is only fair to Bate and Westwood to say that, in their discussion of Sphceroma prideauxianum Leach, they state that " The foot-jaws differ from those of tbe typical species, in having each of the three intermediate joints dilated into an internal flattened lobe, a character which, in conjunction with that of the short plates of the lateral appendages of the terminal segment of the body, seems to indicate a more than specific distinction." They show in their figures the remarkable difference between the maxillipeds of serratum and prideauxianum; the latter being almost undoubtedly a synonym of Leach's Sphceroma curtum, which at any rate has maxillipeds and second maxillae of tbe same pattern. In very near agreement with this pattern is that of the maxillipeds of Sphceroma gigas Leach, which I propose to place in a new genus, though without attempting here the arduous task of re-arranging the other species. Among them Sphceroma rugicauda Leach may be mentioned as having maxillipeds certainly very distinct from those of serratum, yet not in very perfect agreement with those of Sphceroma curtum. Dana says that his Sphceroma calcarea has the maxillipeds nearly as in S. lanceolata, but in the figure to which he refers they agree better with those of S. curtum, and with those which Kossmann represents for a seemingly immature specimen which he doubtfully names Sphceroma obtusum Dana. EXOSPH^EROMA, gen. n. In general appearance agreeing with Sphceroma, but having the penultimate and two preceding joints of the maxillipeds lobed ou the inner side, whereas in the type species of Sphceroma those joints are not lobed. EXOSPHJEROMA OIGAS (Leach). (Plate XXXIX.) 1818. Sphceroma gigas, Leach, Diet. Sci. Nat. vol. xii. p. 346. 1823-5. Sphceroma gigas, Desmarest, Consid. gen. Crust, p. 301. 1840. Sphceroma gigas, Milne-Edwards, Hist. Nat. Crust, vol. iii. p. 205. 1841. Sphceroma gigas, Guerin-Meneville, Iconographie du Begne Animal, Crust, p. 31. 1843. Sphceroma gigas (var. lanceolata), White, Ann. Mag. Nat. Hist. ser. 1, vol. xii. p. 345. 1847. Sphceroma gigas, White, List Crust. Brit. Mus. p. 102. |
