1871.] SURGEON F. DAY ON INDIAN SILUROID FISHES. 287 



commented upon the air-vessel of the Gagata typus, Bleeker ; and 

 it then occurred to me how few inquiries appeared to have been 

 instituted respecting this matter amongst the Siluroid fishes of India, 

 and that what had been made referred chiefly to the genera Clarias, 

 Plotosus, Saccobranchus, Wallago, Callichrous, and Arius. 



Genus Eutropiichthys. 



In the E. vacha, Ham. Buch., the air-vessel is in the form of a 

 tube rather enlarged at either extremity, its diameter being equal to 

 about one-half of that of the vertebral column posterior to it. It 

 closely embraces the body of the third vertebra, lying across it and 

 the large vessels. It then curves backwards and upwards, in the 

 first portion of which course it is slightly protected by a projection 

 on the body of the second vertebra. In the last portion of its extent 

 it is protected by a wide concave expansion of the lateral processes 

 of the first and second vertebrae. This expanded portion of the 

 vertebrae, in which the air-vessel lies, is about equal in width to that 

 of the body of a vertebra. 



Genus Ailia. 



Iu the A. bengaliensis, Gray & Hard., the air-vessel is of the 

 same description as in the E. vacha, with the exception that it is 

 rather more dilated at either extremity. 



I would here remark upon a curious specimen of this species, 

 6| inches long, which I procured at Delhi. It has more or less 

 distinct spines along the whole course of its back, most prominent 

 midway between the eye and the base of the caudal fin. 



Genus Pseudeutropius. 



In the P. garua, Ham. Buch., the air-vessel is contained in the 

 abdominal cavity, but is small, somewhat heart-shaped, with a short 

 prolongation on either side anteriorly. It is firmly attached to the 

 anterior vertebrae, embracing their bodies, and being a little extended 

 laterally on either side. 



Genus Pangasius. 



In the P. buchanani, Cuv. & Val., the air-vessel is contained in 

 the abdominal cavity ; it extends from opposite the base of the pec- 

 toral fin to as far as the end of the anal. A slight contraction exists 

 between its anterior third and the remainder of the organ. 



Genus Silundia. 



In the S. gangetica, Cuv. & Val., the air-vessel is also contained 

 in the abdominal cavity. It is large, and with very thin walls. 



Genus Macrones. 



In the M. cavasius, Ham. Buch., the air-vessel is contained in the 

 abdominal cavity, but not loosely as in the Pangasius. It is of a 



