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Show .871.] FRESHWATER SILUROIDS OF INDIA. 719 larger snow-fed rivers; and it is in these places that all the hill-breed (if we except the Loaches). The rivers of the plains are of course merely the continuations of those descending from the hills ; but the daily rise from melted snows becomes less and less apparent the further we go from their snowy sources. They may be divided into two classes : in the first, as the Indus, Irrawaddy, & c , a fair supply of water is always present ; the second class, as the Soane or the Cauvery, become nearly dry during the hot weather-this result of course being mainly due to their being replenished or not by melting snows. The Siluroids are very extensively distributed in India and Burmah, where they appear to delight in muddy water, avoiding that which is clear, especially if it has a stony or gravelly bed. Some which are marine are only temporary visitors to the fresh waters, whilst others live entirely in fresh water; a few appear to live in estuaries, sometimes ascending the rivers, at others extending their range along the sea-coast, as necessitated by the abundance or absence of food. A few small species always reside in the streams of mountains or in those flowing near their bases, whilst the larger forms prefer the rivers of the plains. Some inhabit tanks only ; others prefer running water; whilst a few are common to both. Some of these fishes aestivate during the hot months of the year. Cold does not appear to suit Siluroids, the number of genera and the species rapidly decreasing as cold climates are approached. Attempting to introduce some on to the Neilgherries a few years since, they perished on the journey and apparently from cold. All of these belonged to the division having the air-vessel not enclosed in bone. But this cannot be assumed as the reason ; for I received two species belonging to this group from the Pegu hills (Akysis and Olyra), whilst I have also obtained Silurus punctatus from an elevation of 2500 feet in the Wynaad; in none of these situations, however, were the rivers snow-fed. The Siluroid forms which I have collected from the snow-fed Himalaya rivers or those streams in the Subhimalayan range all belong to the division with the air-vessel small and enclosed in a bony capsule, as Pseudecheneis, Glyptosternum, Amblyceps, and Exostoma. There are, however, many other genera of this group which are not found on the hills. Countries possessing large and muddy rivers in their plains, such as Burmah, are more suited for Siluroids than such localities as Madras, where the rivers are smaller, the waters clearer, and the beds more stony. When investigating the fish-fauna of large tracts of country this becomes very evident: thus at Hurdwar, near where the river Ganges debouches into the plains, the large Ganges canal commences; both the bed of the river and that of the canal are stony, the waters pretty clear, and Siluroids are rare. Near Dheeri and in the Soane river, which has a pebbly bed, it is exceedingly clear water when floods are absent; but few Siluroids are found there, and these mostly the little Macrones carcio, H. B. A few miles PROC. ZOOL. Soc-1871, No. XLVI. |