244 Records of the Indian Museum. (Von. XVIII, 
toad (Bufo viridis), all in a more or less torpid condition; but no 
Hydrometrid. Indeed, it seemed to us that this family was toa 
large extent replaced by Diptera, such as Halmopota viridescen:, 
Brunetti, which skated on the surface of the water in almost the 
same way as these Rhynchota do. 
The absence of molluscs of the family Melaniidae from the 
Hamun-i-Helmand and the waters connected with it is another 
point worthy of note. In the extreme south of Seistan we found 
one form (Melanoides pyramis var. flavida) in a desert spring, but 
neither living molluscs nor empty shells were found at any place in 
the irrigated part of the country. The absence of species of this 
genus, one of which is not uncommon in adjacent districts, may 
perhaps be due to lack of nutriment or the presence of mineral 
salts in the mud of which they invariably feed. 
In other respects the limitations of the fauna seem to be due 
rather to geographical factors than to any peculiarities of the 
environment. 
GEOGRAPHICAL RELATIONS OF THE FAUNA. 
In considering the geographical relations of the aquatic fauna 
of Seistan five facts must be borne in mind :—firstly, that the 
country lies well within the limits of the Palaearctic Region and 
is separated from India not only by several hundreds of miles 
of desert but also by the great mass of mountains that occupies the 
more important part of Afghanistan and Baluchistan and juts down 
southwards almost to the Mekran coast west of the Indus; secondly, 
that the only waterways that reach it, and probably ever have 
reached it, com@from the east and the north; thirdly, that even 
these waterways are of recent origin in their present course ; fourth- 
ly, that it is much depressed below the surrounding districts, and 
fifthly, that the aquatic fauna, as follows from the third and fourth 
facts, is composed of immigrants from high mountainous tracts. 
These facts account for many of its deficiencies, for example 
for the absence of aquatic Chelonia and Caridea, both of which are 
unknown from the higher regions of Central Asia. To the same ~ 
facts we may trace the paucity of genera in the fish and molluscs, 
contrasted with the relative wealth of sponges and Polyzoa. It 
will be interesting to apply these deductions to the different groups 
of animals that are represented in turn. 
Of the three Batrachia known to inhabit Seistan two are per- 
haps the most widely distributed of all the Palaearctic frogs and 
toads, namely Rana esculenta and Bufo viridis. One of these has 
evidently been stayed in its eastward range by the mass of moun- 
tains to which I have already referred. It does not seem to have pene- 
trated beyond the eastern limits of the Baluch desert, or, from the 
north into the valleys of the western Himalayas, in which the toad 
has madeitself athome. The fact that Rana esculenta is represented 
in Seistan and western Baluchistan by the race dibunda hardly 
affects the situation, as this race itself has an immense range in 
