11 



(a) The Indo-Gangetic Plain is subdivided l)y Blanford into three 

 physiographical " tracts "—a Punjab tract, which also includes Baluchistan; a 

 North-west Provinces tract; and a Bengal tract, which also includes the 



Brahmaputra valley. 



The Punjab tract he places in the south-east corner of the Mediterranean 

 subregion of the Holarctic (Palsearctic) zoological region: the North-west 

 Provinces tract is included in his Cisgangetic zoological subregion: the 

 Bengal tract he includes in his Transgangetic zoological subregion. 



These dispositions, based on the distribution of vertebrata, the present 

 paper does not pretend to criticise : what I think it important to recognize is 

 that, so far as the fresh-water crabs are concerned, the great physical tract 

 known as the Indo-Gangetic Plain is a zoological division also. 



(b) The Indian Peninsula. This physical feature is divided by Blanford 

 into five tracts, namely : Kajputana, Central India, and Kathiawar ; the Deccan ; 

 Behar-Orissa, including also the eastern part of the Central Provinces, Chota 

 Nagpur, and the Northern Circars ; the Carnatic and Madras; and the 



Malabar coast. 



All these physiographical tracts are included in his Cisgangetic zoological 

 subregion. And here again I do not wish to dissent from his conclusion, but 

 only to draw attention to the facts that foi' the Potamonidce the Peninsula as a 

 whole is a zoological division as much as a physical one, and the Malabar 

 coast physical tract is also a distinct zoological subdivision of it. 



(c) Ceylon. Blanford recognizes two physical tracts in Ceylon, namely : a 

 northern tract, practically continuous with the Cisgangetic subregion ; and a hill 

 tract, forming an outlier of the Malabar tract, and also included with that tract 

 in the Cisgangetic zoological subregion. 



I regret that I have not sufficient first-hand knowledge of the fresh-water 

 crabs of Ceylon to include them in my analysis. Miss Eathbun, in her great 

 monograph, gives the following list for Ceylon :— " Potamon " snror (Zehntner), 

 "Potamou atkinsonianuin" (W.-M.), Potamon {Geotelplmsa) enode (Kingsley), 

 Paratelphusa {Oziotelphusa) hydrodromus (Herbst), Potamon {Barytelphusa)^ 

 bouvieri (Rathb.), Parate/phusa (Barytelphusa) guerini (Edw.), and ''Potamon" 

 niffosum (Kingsley). Potamon rugosum is a Paratelphusa. From Zehntner's 

 account, Potamon soror, which is said to resemble P. rugosum, except in the 

 shape of the front, is as likely to be a Paratelphusa as a Potamon. Potamon 

 enode I know from only one specimen, in which the form of the mandibular 

 palp cannot be distinguished. And Potamon atkinsonianum rests upon a 

 specimen of P. koolooense in the British Museum, which, I understand from 

 Dr Caiman, was purchased from a dealer more than fifty years ago, when 

 dealers' localities were, I think, not unimpeachable. 



{d) The Himalayas. This great primary geographical division is cut by 

 Blanford into three physical tracts, namely : Tibet ; the Western Himalayan 



