154 Records of the Indian Museum. [VoL. XVIII, 
¢ gj 
described from the Nazzar or that surrounds 
the Hamun. 
Of the seven species! represented in the collection of the 
Arbitration Commission only three (Discognathus phryne, Adiposia 
macmahont and Schizothorax zarudnyt) are common to it and the 
one of five species recently obtained. This is probably to be ex- 
plained by the fact that the former collection was mainly if not 
exclusively of fluviatile origin, while the other was paludine or 
lacustrine, or at any rate not from rapid-flowing water. 
We may now consider the question of structural modification 
in the Seistan fish, distinguishing carefully between those peculi- 
arities they brought with them from their mountain home and 
those that may have been evolved in the basin of the Helmand. 
A striking feature of the fish-fauna of Seistan is the de- 
generate nature of the scales. The degeneracy is not of the 
same kind, however, in all the species. In the Schizothorax, the 
Schizopygopsis and the Schizocypris—as, indeed, in all Schizo- 
thoracinae—the scales are small, partly buried in the skin and (if 
not completely degenerate) non-imbricate or almost so in the 
living fish, except in the anal and scapular regions. In Discogna- 
thus phryne they have almost completely disappeared on the 
ventral and dorsal regions, remaining normal in shape and size, 
but somewhat deciduous, on the sides; in Scaphiodon macmahont, 
while normal on the sides and back, they are absent or degenerate 
on the ventral surface. In the three Cobitidae scales are al- 
together absent or merely vestigial. Oniy in Discognathus adiscus 
does the lepidosis appear quite normal, and in this species the 
scales are so deciduous that carelessly preserved specimens are 
almost naked. 
The Schizothoracinae are the dominant fish of the streams 
and marshes of the high plateau of Central Asia, the waters of 
which they share with the Cobitidae, most of which are practically 
scaleless. Smallsize or absence of scales is, therefore, a conspicuous 
feature of the fish-fauna of that region, and the plates of Herzen- 
stein’s * great monograph offer in this respect a striking contrast to 
those illustrating the Cyprinidae in Day’s Fishes of India. Ui, 
therefore, it had been only the Schizothoracinae and the Cobitidae 
which had manifested in Seistan signs of degeneracy in the scales, 
all that could have been said would have been that they were 
descended from species that possessed this feature, and provided 
no evidence that life in a low-lying country was affecting ancestral 
characters in this respect. The case would have been to some 
extent parallel to that of Salmonidae confined in land-locked 
waters, for the small size of the scales in both the Schizothoracinae 
and the Salmonidae is probably due to the importance of a supple 
‘ reed-country ’ 
1 Discognathus variabilis, Scaphiodon macmahoni, Schigothorax sarudnyt, 
Schizopygopsis stoliczkae, Nemachilus stoliczkae, Adiposia rhadinaea, Ad:posia 
macmahont. 
2 Herzenstein, Fische, in Wiss. Res. Przewalski Central-As. Reis. Zool., IKI, 
2), (1888). 
