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XLI. In the order PLECTOGNATHI, several of the 

 family Gymnodontes are found ascend- 

 ing rivers for some distance, espe- 

 cially species of the genus Tetrodon, but they do not appear 

 to be considered fit for food anywhere (except some sea 

 species amongst the Andamanese). Still in Burma, a closely 

 allied fish, Xenopterusnaritus, is extensively taken in the lower 

 provinces, and esteemed as food by the people of the country. 

 XLIL In the SUB-CLASS CHONDROPTERYGII, order 

 PLAGIOSTOMATA, there are some 

 Cartilaginous fishes. species which ascend rivers for preda- 



ceous purposes, but are not esteemed 



as food. Amongst the family of sharks, the Carcharias Gange- 

 ticus ascends rivers, but not very often far beyond tidal influ- 

 ence; however, I have seen it at Cuttack, and in the Pegu river : 

 whilst a species of saw-fish, Pristis, is likewise found to pro- 

 ceed as high; neither breed in the rivers. Amongst the Try go- 

 nidce, the T. uarnak is also frequently found above tidal 

 influence. 



R/ESPIKATION OP INDIAN PISHES. 



XLIIL Before commencing the subject of the sudden 

 appearance of fishes in Indian tanks 

 ***** ^lls of rain, and how they mi- 

 grate during periods of floods, a lew 

 observations are necessary upon how they respire, as some 

 remarkable variations from the usual manner are observable, 

 evidently to enable certain tropical forms to resist causes 

 which are not in existence in most extra-tropical regions. 

 Three modes of respiration are perceptible : first, the usual 

 one of oxygen obtained, except under peculiar circumstances, 

 from air in solution in the water, and which is separated 

 at the gills ; these may be termed for description, not defini- 

 tion, " water-breathers," as the carps, Cyprinince, or some of the 

 siluroids, as Macrones, and they can live, as a rule, without 

 rising to the surface. If any of these fishes are placed in a 

 globe of water at a moderate temperature, with a diaphragm 

 of net precluding their reaching the surface, their breathing 

 remains unaffected. If, on the contrary, a bandage is 

 stitched around the gill-opening, precluding their employing 

 their gills, they rapidly become suffocated. This result in 

 another form is perceived to occur in India, either artificially 

 or naturally. Thus, when the water in which they reside 

 becomes suddenly changed from clear to very muddy, their 

 gills become choked, respiration is impeded, and death results. 



