10 



(4) A Burma-Malay Territory, includiug all that part of the Indian 

 Empire that lies south of the new political province of Assam and east of the 

 Bay of Bengal. Here we find representatives of three of the four subgenera 

 of Potamon and of three of the six subgenera of Paratel-phusa, six of the 

 Potamons, but none of the Paratelphusas, being exoteric. 



(5) A Peninsular Territory, including the Indian Peninsula south of the 

 Indo-Gangetic Plain. How far Ceylon is included I cannot say : my reasons 

 for excluding Ceylon from consideration are stated elsewhere. In this centre 

 no species of the subgenus Potamon is found, nor any Potamon at all, except 

 Potamon [Geotelphusa) enode, which, according to Henderson, has been met 

 with in South India. With this exception, all the fresh-water crabs of the 

 Peninsula are Paratelphusas and Gecarcinucus. Of the fifteen species of 

 Paratelphusa proper to this territory, eight belong to the subgenus Barytelphusa, 

 which is the predominant Paratelphusa subgenus of the Eastern Frontier 

 territory, and three belong to the subgenus Globitelphusa, which is not found 

 elsewhere out of the Eastern Frontier territory. 



(6) The Indo-Gangetic Plain, including all the territory south of the 

 Himalayan foothills and north of the Central Indian plateaux, from the Indus 

 to the Brahmaputra. In this territory two species of the Potamon subgenus 

 Acanthotelphusa are found, and no other species of the genus Potamon. Its 

 other species belong to the Paratelphusa subgenera : Paratelphusa (one), 

 Barytelphusa (three), Oziotelphtisa (one), and Phricotelphusa (one). Only 

 two of its species are peculiar to it, and one of these is perhaps only a race 

 of an Eastern Frontier species. It looks as if this territory had been recently 

 colonized from the East and from the South. 



Although the distribution of the Indian fresh-water crabs does not at all 

 points fit the schemes either of Blanford or of Wallace, there is nothing about 

 it that is actually discordant with either of those schemes. The chief point of 

 difference is that in the case of the Potamonidce — ^(1) the Indo-Gangetic Plain 

 is quite sharply separated from the Peninsula, and (2) the North-eastern 

 Frontier territory is much more independent of Wallace's Indo-Chinese sub- 

 division, and of Blanford's Transgangetic subdivision, of the Oriental region. 



Blanford's zoological subregions are based entirely, and Wallace's very 

 largely, on vertebrates ; and it has therefore seemed to me more profitable to 

 compare the distribution of the Indian Potamonidoi, not with Blanford's 

 zoological subregions, but with the physiographical divisions upon which his 

 zoological divisions are built. 



Blanford divides the area of the Indian Empire into five primary 

 physiographical regions, namely — {a) the Indo-Gangetic Plain, {b) the Indian 

 Peninsula, (c) Ceylon, {d) the Himalayas, and {e) Assam, Burma, and the 

 parts east of the Bay of Bengal. 



