1871.] FRESHWATER SILUROIDS OF INDIA. 709 



The genus Arius is found throughout the seas and estuaries of 

 India, Ceylon, Burmah, the Andaman and Nicobar Islands ; it 

 also extends to most of the tropical regions. In India it is strictly 

 marine, but enters rivers often to a long distance from their mouths. 

 Whether it breeds in the fresh waters is questionable. 



Osteogeniosus valenciennesii, Bleeker. 



In a specimen from Moulmein, taken in the river, the air-vessel 

 was large, heart-shaped, having an internal longitudinal septum, and 

 not enclosed in bone. 



Geographical distribution. — A marine genus, extending through 

 the seas of India to the Malay archipelago. Some enter the mouths 

 of rivers. 



Pangasius buchanani, Cuv. et Val. 

 Pimelodus pangasius, H. B. pi. 33. f. 52. 



Air-vessel large, extensive, and divided into three portions. The 

 anterior is somewhat heart-shaped, considerably the largest, and ex- 

 tends from the commencement of the vertebral column to nearly 

 opposite the posterior extremity of the pectoral fin. Its remaining 

 portions are narrow, compressed, and continued to opposite the 

 middle of the anal fin, amongst the muscles covering the haemal 

 spines. It then becomes narrow and reduplicated on itself for a 

 short distance. On removing the front wall of its first or largest 

 portion, its interior is seen to consist of two pear-shaped cavities, the 

 bases of which are inferior and lateral, whilst they coalesce anteriorly ; 

 the whole of the posterior half of this portion is cellular ; and so is 

 the small intermediate space between the two uncelled pyriform por- 

 tions. The two posterior divisions of the air-vessel have valvular- 

 shaped folds partially subdividing its interior. 



Geographical distribution. — The Indian species is found within 

 tidal influence, as well as inland in the larger rivers far beyond the 

 tides. The genus extends through Burmah to the Malay archi- 

 pelago. 



Genus Psetjdeutropius, Bleeker. 



Schilbichthys, sp., Bleeker. 



Air-vessel in P. garua, H. B., small and somewhat heart-shaped, 

 it is closely attached to the bodies of the anterior vertebras; its 

 external fibrous covering is of moderate strength. In P. atheri- 

 noides, Bloch, it is of a large size, as wide as the abdominal cavity, 

 and on removing its front wall a longitudinal septum is seen dividing 

 it into lateral portions, which, however, communicate anteriorly. In 

 some there is a further subdivision in its posterior portion. In some 

 of the larger species (as P. murius, H. B., and P. goongwaree, Sykes) 

 the air-vessel is larger than in P. garua, and comparatively consider- 

 ably smaller than in P. atherinoides, Bloch. P. garua, in which 

 the adipose dorsal is so small, and altogether absorbed in the adult, 



