428 Memoirs of the Indian Museum. [Voi,. V, 



large rivers to breed, the Persian Gulf ascending the Tigris, and the coast of Siam 

 entering lakes. 



Suborder 0STABI0PHYS1. 



Family SILURIDAE. 



Subfamily CLARIINAE. 



Genus PLOTOSUS, Lacépède. 



Plotosus canius, Hamilton Buchanan. 



1803. Platystacus anguillaris, Rüssel, Vizag. Fish., II, p. 51. 



1822. Plotosus canius, Hamilton Buchanan, Fish. Gang., pp. 142, 374, pi. xv, fig. 44. 



1878. Plotosus canius, Day, Fish. Ind., p. 482, pi. cxii, fig. 3. 



1889. Plotosus canius, Day, Faun. Brit. Ind., Fish., I, p. 113, fig. 47. 



Russel mentions two specimens, one of which was caught in a river, measuring 

 two feet and seven inches in length, and the other, which was obviously caught in the 

 open sea and was the original for Russel's plate no. clxvi, measuring seven inches 

 in length. The latter was undoubtedly a specimen of Plotosus anguillaris (Bloch) 

 which is a marine species, but the former from its size as well as from its estuarine 

 character must have been a specimen of Plotosus canius, H.B., which Russel described 

 under the name P. anguillaris, Bloch. 



There are altogether twenty-eight specimens in the collection from different 

 parts of the lake, obtained throughout the year. Young specimens were mainly 

 obtained after the rains in the outer channel. The following list indicates roughly the 

 distribution of the species in the lake. 



2 specimens Channel north of Arupâtnâ (south side of Satpara) 

 2 ,, Barkul Point 



1 specimen Off Mahosa 

 4' specimens Between Samal Island and Mainland 



2 ,, Satpara 

 2 ,, Off Satpara 



13 ,, Serua Nadi (depth 5ft. to gft.) 



2 ,, South-eastern corner of the lake 



In every specimen there is an anal papilla, which is tubular and elongated, 

 immediately behind the vent. It is enclosed from behind by a large spongy and 

 arborescent (dendritic) organ. In very young specimens this arborescent organ ap- 

 pears to look like a gill-book-form of respiratory organ. The whole of it is covered 

 over by the ventral fins, which extend beyond it over-lapping a portion of the anal fin. 

 The ventral fins thus probably protect the organ from mud, on which the fish usually 

 rests, being a bottom fish. The arborescent organ would be soon choked with mud if 

 not thus protected. The function of the organ is evidently respiratory and not sexual 

 as it is found fully formed even in very young specimens. 



IO-ix-14, 



measurin 



g 60 mm. and 

 28 mm. 



2i-ix-i4, 



» î 



256 mm. and 

 250 mm. 



12-IX-13, 



? » 



27 mm. 



io-ix-14, 



î > 



76 mm. to 

 80 mm. 



March 1914, 



?» 



283 mm. to 

 316 mm. 



, 17-IX-13, 



? » 



42 mm. and 

 120 mm. 



i8-ix-i4, 



5 > 



33 mm. to 

 68 mm. 



? 



•■ 



485 mm. and 

 496 mm. 



