1010 



MB. L. A. BOREADAILE ON CRXJSXACEANS [DeC. 13 



females belonged to S. gibherosus, and that the true females of 

 S. marmoratws will be found to possess the characteristic third 

 maxillipeds of: the male, at least in form if not in length. I'or 

 this conclusion, however, there is no evidence whatever. The 

 other authors make no reference to the sexual characters. In 

 Mr. Grardiner's collection there are seventeen females and thirty 

 males from Eotuma, all taken in the same localities and in the 

 same position, namely, on the " reef-flat " and "rough-zone" of 

 the outer reef. The males can be sharply divided into two groups, 

 having the marmoratus- and gihherosus-ohav&ctanstics respectively. 

 The females, however, are all of the gibherosus type. 



Taking into consideration the statements of Ortmann and de 

 Man, these facts point, I think, to the conclusion that Saron 

 marmoratus is a species with a dimorphic male, one form resembling 

 the female, and the other differing from it in the length of the 

 third maxilliped * and first pair of legs and in the form of the last 

 joint of the third maxilliped. This appendage is well described 

 and figured by de Man (Zool. Jahrb. loc. cit.). 



Should the above surmise prove to be correct, the question will 

 arise whether the dimorphism of the male be permanent or occur 

 only at the breeding-season, as has been shown by Faxon [Am. 

 Journ. Sci. xxvii. (1894)] to be the case for the males of Oambarus. 

 On this point there is no direct evidence. The presence, in Mr. 

 Gardiner's and other collections, of both forms of the male, taken 

 at the same time, might seem rather to negative the latter sug- 

 gestion ; but in view of the fact that tropical marine forms tend to 

 breed all the year round, the question must still remain open. 



Some interesting remarks on dimorphism in male Crustacea 

 are contained in the Report on the Isopoda of the ' Lightning ' 



' According to Ortmann this difference in the length of the third maxilliped 

 is not so marked in individuals from East Africa (fSeuion's Forschungsreisen, 

 loc. cit.). His note, however, on this point is somewhat obscure, and it is 

 quite possible that his speci mens' were ^i6if;-06«s-males without a spine on the 

 fifth merus. 



