6. 



$. 



2- 



26 



29 



28 



34 



37 



35 



8 



8-5 



9 



18 



18 



19 



60 



63 



72 



63 





68 



962 ox A NEW RIVER-CRAB FROM NEW GUINEA. [DeC. 15, 



Measurements in inillimetves : — 



6 . 



Length of carapace 29 



Breadth of carapace 39 



do. front 9 



do. fronto-orbital margin ... 18'5 



Length of larger cheliped 76 



do. second walking-leg 79 



do. third walking-leg 75 



For comparison I give the corresponding measurements of thi-ee^ 

 specimens of G. jacquemoniii * in the Natural History Museum : — 



c? . 6. 2- 



Length of carapace 33 30 31 



Breadth of carapace 48 44 45 



do. front 8-5 8 8 



do. fronto-orbital margin .. . 21 19 21 



Length of larger cheliped 74 68 68 



do. second walking-leg 68 63 67 



do. third walking-leg 64 58 61 



Meniarhs. — G. ingrami agrees with G. jacqitemontil in the 

 strongly inflated branchial regions and in the form of the efferent 

 branchial orifices. The latter are bounded above by a prominent 

 lip formed by the everted edge of the epistome and below by the 

 enlarged terminal lobe of the first maxillipeds, wiiicli is left largely 

 exposed when the third maxillipeds are closed. Whether these 

 characters are adequate to justify the alliance in one genus of 

 two species so widely sepaiated geographically may perhaps be 

 disputed when the systematic arrangement of the Potamonidse 

 comes to be more closely examined than it has hitherto been. For 

 the present, the genus appears to be as well defined as are most 

 of those forming the family. It seems to me doubtful, however, 

 whether the subfamily Gecarcinucina:', formed for its recej)tion by 

 Miss Bathbun, can be sustained. The propoi'tionate width of the 

 front, selected by that author as the most important distinction 

 in her key to the subfamilies and genera (Nouv. Arch. Mais. 

 Paris, (4) vi. p. 247), does not hold good, as the measiu-ements. 

 given alcove show, even for G. jacqitemontii, and it is still less 

 distinctive in the new species. On the other hand, it seems 

 probable that there are still to be discovered among the Pota- 

 monidfe characters more trustworthy as indications of afiinity 

 than those hitherto employed. For example, the remarkable 

 form of the mandibular palp, as figured by Milne-Edwards for 

 G. jacqueinontii, recurs not only in the species here described 



* These specimens, presented bj' Mr. R. C. Wroughton, are from Kaman Eiver, 

 Bombay. As the measurements show, they are smaHer than the t\'pe-specimens of 

 Mihie-Edwards redescribed bj- Miss Rathbun, and have the carapace relatively 

 narrower, but in other respects they agree so closely with Milne-Edwards's figures as. 

 to leave no doubt that they belong to the same species. 



