720 ON THE FRESHWATER 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 

 SiluridEe, 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) A/eysis ; found 

 in India, Burmah, and the Malay archipelago, (J) Macrones, (8) 

 Callichrous, (9) Wallayo, (10) Arius, (11) Osteoyeniosus, (12) 

 Batrachocephalus, (13) Pangasius, and (14) Plotosus. As, how- 

 ever, (10), (11), (12), and (14) are, strictly speaking, marine, only 

 entering rivers for predaceous purposes, I shall omit them, thus re- 

 ducing the total to ten. 



2. Air-vessel more or less enclosed in Bone. 



Genera restricted to India, (1) Ailia, (2) Ailiichthys, (3) Sisor, 

 (4) Bayarius, and (5) Amblyceps ; extending also into Burmah, (6) 

 Saccobranchus, (7) Silundia, (8) Eutropiichthys, and (9) Gayata; 

 found in an intermediate hilly district, (10) Pseudecheneis ; also ex- 

 tending into Burmah, (11) Exostoma ; restricted to Burmah or pe- 

 culiar to it and the Malay archipelago, none ; found in India, Burmah, 

 and the archipelago, (12) Clarias, (13) Hemipimelodus, and (14) 

 Glyptosternum, which last, however, only appears to have one re- 

 presentative 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 won- 

 dered 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 freshivater, 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 



* This intermediate billy district appears to commence from about Darjeeling 

 in the Subhmialayas to a line including the Khasia hills on the other side of 

 Bramahputra, and extends to the hilly regions towards or in Burmah. It has 

 yet to be fully explored zoologically. 



t I do not enter more fully into the distinction between the Siluroids of 

 India and Burmah, as my collections of the fishes of this last district have not 

 yet been thoroughly worked out and are in Europe. 



