20 Records of the Indian Museum. Vor. XVILE 
Limnaea hordeum (otherwise known only from lower Mesopo- 
tamia) the only true western form. 
The Helmand, which, so far as the aquatic fauna is concerned, 
is the connecting link and the only highway for aquatic animals 
between the mountains of Baluchistan and eastern Afghanistan 
and the Seistan basin (or, indeed, between Seistan and all other 
countries), has naturally a molluscan fauna identical with that of 
the basin into which it flows. In the small springs of the desert, 
the water of most of which is more or less saline, only a few very 
tolerant species (e.g. Gyraulus euphraticus and Corbicula fluminalis, 
both of great geographical range) can live, and we found but one 
form (Melanoides pyramis var. flavida) probably peculiar to situa- 
tions of the kind. It occurs in Persian Baluchistan as well as the 
Afghan-Baluch desert. Limnaea persica has only been found as 
yet in the southern part of the Persian plateau and in the basin 
of the Lora river in the eastern part of the desert. 
The molluscan fauna of Persian Baluchistan is still imperfectly 
known, but the inclusion of a species of Melanopsis indicates the 
presence of a true western Asiatic element absent from other parts 
of the area under consideration. 
The general absence of this western Asiatic element is per- 
haps the most striking feature of the fauna considered as a whole. 
Another point to be noted is the absence of certain large and con- 
spicuous Palaearctic forms (e.g. Limnaea stagnalis) common in 
Kashmir at altitudes no higher than those of the Quetta district. 
This, however, does not imply that the fauna is essentially Ori- 
ental in the strict zoogeographical sense, for conditions of life are 
clearly inimical to large forms. The fauna is a starved one in 
which only species of great adaptability can survive. Such mol- 
luscs as Vivipara hilmandensis and Lamellidens marginalis, though 
evidently of Oriental origin, have spread into Palaearctic districts 
on the limits of their range, while the species of Limnaea, though 
here described as distinct, have a clear Palaearctic facies and most 
of them are probably descended from Palaearctic rather than true 
Indian forms, from which they differ considerably in all but one 
instance. The species of Gyraulus and Segmentina, though they 
occur in Oriental districts, are closely related to and probably de- 
rived from European forms. 
The molluscan fauna of Seistan and Baluchistan, therefore, 
has little true geographical significance. 
BIONOMICS. 
The bionomics of the molluscan fauna of the inland waters of 
Baluchistan and Seistan are perhaps more interesting than its 
geographical distribution, but here again characters are negative. 
The fauna is one that lives habitually in water of abnormal 
chemical composition, for even potable water in these countries 
contains far more than its usual allowance of mineral salts (see 
p. 15, antea). ‘The molluscs have not, however, responded to the 
