930 DR. W. T. CALMAN ON 



the carpus " ragt nur ein wenig unter die Antennenscbuppe nacli 

 vorn," while in our specimen the dactylus beais only two teeth 

 and the cai-pus may extend beyond the tip of the antennal scale. 

 In all other respects, however, Hilgendorf's description applies so 

 well to our specimens that their specific identity can hardly be in 

 doubt. 



The existence of an aifinity between this species and the 

 Bithynis gaudichavdii of Chile and Peru, asserted only in a 

 hesitating manner by Hilgendorf, is fully accepted by Couti^re, 

 but denied by Ortmann, who considers that the resemblance does 

 not extend beyond a single character (the lack of a hepatic spine) 

 which may easily be supposed to have arisen by convergence. 

 Ortmann's view is strongly supported by the variability of this 

 character in the present series of specimens. I have examined 

 the appendages of both species for other evidence of affinity 

 between them, and have failed to find it. The branchial system 

 and the mouth-parts of both are very similar to those of several 

 species of Palcemon with which I have compared them. Only in 

 one point do the mouth-parts of B. hildehrandti present anything 

 unusual, and that is the reduced size of the epipodite of the 

 first maxillipeds, but this constitutes no resemblance to B. gaudi- 

 chaudii, in which the epipodite is quite as large as in the species 

 of Palremon examined. On the other hand, the differences in 

 general aspect between the two species are considerable ; B. hilde- 

 hrandti has the chelipeds hardly differing in the two sexes, 

 slender, symmetrical, smooth, with the carpus equal to the merus, 

 and the fingers ai'med with only a few small teeth near the 

 base ; B. gaudichcmdii is a very much larger species, with the 

 chelipeds very stout, much more strongly developed in the male 

 than in the female, very unequal on the two sides of the bod}^, 

 beset with spiny tubercles, with the carpus shorter than the 

 merus, and the fingers of the larger chela toothed for half their 

 length or more. If it be advisable to maintain the genus Bithynis 

 (which seems to me doubtful) it must be for the South American 

 species alone, and B. hildehrandti must be transferred to the genus 

 Palcemon. 



The varia,biHty of the hepatic spine in this species recalls the 

 cases of " mutation " recently described by Bouvier in ceitain 

 Atyidfe. It resembles these cases in its discontinuity, only one 

 individual ovit of those examined being in any way intermediate 

 between the two forms ; and it further resembles some of them 

 at least in the fact that it is geographically limited, for the 

 specimens of the two forms come from difierent localities. Both 

 of these points, however, require to be tested by further collecting. 

 It differs from Bouvier's cases in that it concerns only a single 

 chai'acter, and one which, were it not for its constancy in other 

 Palfemonidee, might be regarded as of trivial importance. 



The large size of the eggs may be taken to indicate an abbre- 

 viation or suppression of the larval development, and this is 

 likely to be associated, as it is in some other Palsemonidse, with 



