1900.] FROM THE FALKLAND ISLANDS. 653 



Guerin-Meneville makes oE 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 

 serratam 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 the 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 prideati.vianum ; the latter 

 being almost undoubtedly a synonym of Leach's Sphceroma 

 curtum, which at any rate has maxillipeds and second maxillae of 

 the 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 maxil- 

 lipeds 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^BOMA, geu. n. 



In general appearance agreeing with Sphceroma, but having the 

 penultimate and two preceding joints of the maxillipeds lobed on 

 the inner side, whereas in the type species of Sphceroma those 

 joints are not lobed. 



ExosPH^ROMA GIGAS (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 

 Eegne Animal, Crust, p. 31. 



1843. Sphcerovia gigas (var. lanceolata). White, Ann. Mag. Nat. 

 Hist. ser. 1, vol. xii. p. 345. 



1847. Sphceroma gigas, White, List Crust. Brit. Mus. p. 102. 



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