DECAPOD CRUSTACEA FROM MADAGASCAR. 927 



Pal^mon (Eupal^mon^) RiTSEMiE de Man. 



Pcdcemoni^Eupalcemon) ritsemce de Man, Zool. Jahrb., Abth. Syst. 

 ix. 1897, p. 774: op. cit. x. 1898, pi. xxxvii. fig. 70. 



Pcdcemon ritsemce Coutiere, Ann. Sci. Nat. Zool. (8) xii. 1900, 

 p. 314, pi. xiii. figs. 32-33 «. 



Localities. Manambato, streams running into Lake Rasoabe, 

 3 males, 8 females {Methuen) ; Ivondro, 6 males (^Methuen) ; 

 Ambilo, 2 males (Methuen) ; Tamatave, 1 male, B.M. 82.6. 



The specimens collected by Mr. Methuen belong, without 

 doubt, to the same species as a specimen in the Museum Collec- 

 tion from Tamatave, determined by Mr. Miers as P. idee Heller. 

 They differ conspicuously from typical specimens of that species, 

 however, in the fact that the surface of the carapace and of the 

 tail-fan is completely smooth or presents only very minute and 

 iuconspicuoQS traces of spinules, while the chelipeds of the second 

 pair are very finely scabrous. Since ISTobili has described a 

 smooth or nearly smooth variety of P. idee from New Guinea, 

 and Coutiere records a similar example from Madagascar, this 

 character may not be of specific value. The chelipeds of the 

 second pair are shorter, in relation to the body-length, than in 

 Couti^re's specimens of P. idee, the longest being only a.bout 

 14- of that length, and most of them being actually shorter. 

 Although the carpus is, except in three instances, longer than 

 the chela, the diflerence is very much less than is shown by 

 Ooutiere's measurements in specimens of P. idee of similar size, 

 and the fingers are always much more than half the length of the 

 palm. On the other hand, the rostral formula in nearly all cases 

 falls within the somewhat narrow limits assigned to the variations 

 of this character in P. idee, and the armatui'e of the fingers agrees 

 precisely with Coutiere's description. 



In all the points mentioned in which these specimens difier 

 from the descriptions of P. idee., they approach Coutiere's account 

 of the form which he identifies with P. ritsemce de Man. Our 

 smaller specimens, however, which alone are directly comparable 

 with Coutiere's largest, have the second chelipeds more asym- 

 metrical and apparently a good deal stouter, the chela itself, and 

 especially the palm, being relatively a little shorter. The larger 

 specimens have many of the proportions rather different, the 

 greater relative length of the palm in most of them being 

 noteworthy. Finally, in the specimens now examined, the pos- 

 terior perseopods are, on the whole, stouter than in those 

 previously described in this species, the ratio of length to breadth 

 in the propodus of the fifth pair varying from 25 to 21, while 

 de Man gives the ratio as from 35 to 25 and Oouti6re as 25. 



On the whole, the balance of characters seems to be in favour 

 of regarding our specimens as older individuals of the species to 

 which Coutiere's specimens belonged, which he has recorded under 

 the name of P. ritsemce ; whether they really belong to de Man's 

 species is, perhaps, a little more doubtful ; and I am not at all 



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