As to the forms here described as varieties, I should of course, as a 

 believer in the origin of species mainly by the accumulated selection of small 

 adaptive variations, Hke to think that they were geographical racps, or incipient 

 species. But I do not know enough about them to say that they are so, or 

 even to think that they are so. In fact, I do not always know what they are : 

 there may be cases of individual abnormality among them. 



In most cases where forms that seem to me to be varieties have been 

 specifically named by other authors, I have used those names, as I do not like 

 interfering with other people's finger-posts. 



Geographical Distribution. — In the present confused state of the 

 system, I do not think it safe to discuss the geographical distribution of the 

 Potamonidce : I shall restrict myself to a consideration of the manner of disposal 

 of the family within the limits of the Indian Empire, beginning with certain 

 bare statements regarding the composition and disposition of the three Indian 

 genera. 



1. The genus Potamon. The Indian species of this genus are arranged in 

 four subgenera : Potamon, Potamiscus, Geotelphusa, Acanthotelphusa. 



a. The subgenus Potamon includes twenty-eight or twenty-nine Indian 

 species and varieties : the type is the palsearctic Potamon fliimatile Latr., which 

 is found in South Europe and North Africa. The Indian species are found 

 in Baluchistan, the Afghan border, all along the Himalayas from west to east, 

 and thence still further eastwards to China and southwards to the Malay 

 Peninsula and Islands. 



No species of the subgenus Potamon has yet been found in the Indian 

 Peninsula. 



No species of the subgenus Potamon has yet been found in the Indo- 

 Gangetic Plain, though one species {P. JiuviatUe, var. ibericum) has been found 

 in the valley of the Jhelum at 2000 feet. The species said to come from 

 Ceylon depends upon a dealer's locality of more than fifty years ago, and I do 

 not accept it. 



b. The subgenus Potamiscus includes two or three Indian species : all three 

 belong to the Eastern Himalayan region, but one of them (P. sikkimense) has 

 also been found at Ajmere in Rajputana — extra-peninsular. 



c. The subgenus Geotelphusa includes three Indian species : the type is 



Potamon {^Geotelphusa) obtusipes, Stimpson, from the Japanese Islands. Two of ' • . S'l) 

 the Indian species occur in the Eastern sub-Himalayan region, one of them 

 being also found in Burma. 



One species {P. enode, Kingsley) ^ is said to occur in the Indian Peninsula. 



1 I have seen only one specimen of Geotelphusa enodis (Kingsley), and its mouth-parts were so 

 much stuck together that I could not make out the form of the mandibular ]ialp, so that I am not 

 perfectly satisfied that it really belongs to the Potamon clan. 



