OCR Text |
Show 720 ON THE FRESHW'ATER SILUROIDS OF INDIA. [Dec. 5, distant is the narrower, sluggish, but deeper and muddy Poon river, where Siluroids abound. If we now examine the foregoing twenty-eight genera of Indian Siluridae, fourteen will be found to have the air-vessel free in the abdominal cavity, and the remaining fourteen to have it more or less enclosed in bone. For facility of description I will divide them thus:- 1. Air-vessel free in the Abdominal Cavity. Genera restricted to India, none; extending also into Burmah, (1) Rita, (2) Hara, (3) Pseudeutropius, and (4) Silurus; found in an intermediate hilly district*, (5) Olyra; restricted to Burmah, none ; common to it and the Malay archipelago, (6) Akysis ; found in India, Burmah, and the Malay archipelago, (7) Macrones, (8) Callichrous, (9) Wallago, (10) Arius, (11) Osteogeniosus, (12) Batrachocephalus, (13) Pangasius, and (14) Plotosus. As, however, (10), (11), (12), and (14) are, strictly speaking, marine, only entering rivers for predaceous purposes, I shall omit them, thus reducing the total to ten. 2. Air-vessel more or less enclosed in Bone. Genera restricted to India, (1) Ailia, (2) Ailiichthys, (3) Sisor, (4) Bagarius, and (5) Amblyceps; extending also into Burmah, (6) Saccobranchus, (7) Silundia, (8) Eutropiichthys, and (9) Gagata; found in an intermediate hilly district, (10) Pseudecheneis; also extending into Burmah, (11) Exostoma ; restricted to Burmah or peculiar to it and the Malay archipelago, none ; found in India, Burmah, and the archipelago, (12) Clarias, (13) Hemipimelodus, and (14) Glgptosternum, which last, however, only appears to have one representative in the Malay archipelago. Out of the foregoing twenty-four genera as restricted, seven only appear to extend from India throughout to the Malay archipelago, of which four have the air-vessel free and three have it enclosed in bone ; but, of these last three genera, Clarias is distributed through Africa and Asia so very widely that its presence is not to be wondered at, whilst only three species amongst the last two genera are recorded from the Malay archipelago. This brings one to the proposition that the necessity for this bony capsule to the air-vessel is greater in India and Burmah than in the Malay archipelago ; and, secondly, one is naturally led to the conclusion that this protection is for the freshwater, not for the marine, Siluroids. It will now be necessary to briefly consider whether amongst these freshwater groups any general law of distribution holds goodf *_iTb_S i?t.ennediate hillJ district appears to commence from about Darjeeling in the Subhimalayas to a line including the Khasia hills on the other side of J-ramahputra, and extends to the hilly regions towards or in Burmah. It has yet to be iully explored zoologically. T „-I d°_n^t e u tfr m o r e ful1^ int0 the distinction between the Siluroids of India and Burmah, as m y collections of the fishes of this last district have not yet been thoroughly worked out and are in Europe. |