FRESH-WATER DOLPHINS. 37 



the existing fresh- water dolphins may have been derived from a family which was 

 originally widely distributed and marine, and that they have managed to survive 

 solely by having taken to a fresh- water life. The isolated distribution of the three 

 living species is somewhat in favour of the latter view. 



Ths Gangetic The Gangetic dolphin, or susu (Platanista gangetica) is the 



Dolphin. typical representative of the family, and inhabits the Indus, Ganges, 

 and Bramaputra Kivers, with their larger tributaries, from the regions where they 

 leave the mountains to the sea. It is characterised by its long and compressed 

 beak, which is slightly enlarged at the extremity; by the back-fin being rudi- 

 mentary and replaced by a low ridge ; by the flippers being triangular and fan- 

 shaped; by the eye being very minute and rudimentary; and by the blowhole 

 forming a longitudinal slit. The conical and cylindrical teeth are rather large ; 

 and while they are sharply pointed in the young, in the adult they become much 

 worn down by use. Towards the extremities of the jaws they are so closely placed 

 as to bs almost in contact with one another. The skull is characterised by the 

 development of enormous crests at the root of the beak, which almost meet in the 

 middle line above the latter. In the males the beak is much shorter than in the 

 females ; and there are generally about thirty teeth on each side of the jaws. The 

 colour of the animal is blackish throughout. Females are larger than males ; the 

 usual length of adults varies from 7 to 8 feet, but a specimen from the Jumna is 

 said to measure upwards of 12 feet. 



The Gangetic dolphin is perfectly blind; and, indeed, as Mr. 

 Blanford observes, sight would be perfectly useless to it in the turbid 

 waters of the Indus at all seasons, and in the Ganges and Bramaputra at most 

 periods of the year. It is never seen out at sea ; but appears to be to a certain 

 extent migratory in the rivers, since none are observed in the Hughli at Calcutta 

 during the hot season from March to June, although they are commonly visible in 

 the cold months from October to March. That they also remain in the tidal waters 

 of the river during the rainy season from June to October is proved by the circum- 

 stance that they are then frequently caught in fishing-nets, although the animals 

 rarely show themselves above water. " This fact," writes Dr. Anderson, to whom 

 we are indebted for a full account of the habits of this interesting Cetacean, " may 

 be accounted for on the supposition that the strength of the current is so great when 

 the Hughli is full that the dolphin is prevented from rising to the surface in the 

 marked manner it does during the cold weather, when the current has slackened 

 and there are comparatively quiet reaches in which it can disport. The disturbed 

 state of the river when it is swollen doubtless renders the presence of the dolphin 

 very difficult of detection, for at such times it will simply expose its blowhole too 

 restricted a surface to be noticed on the troubled waters. In the cold weather its 

 presence can easily be detected, without its being seen, by the blowing sound it 

 makes when it rises to breathe ; but, during the rains, the rush of water effectually 

 drowns this means of becoming aware of its existence." This dolphin has been ob- 

 tained one thousand miles above Calcutta ; and its upward range appears to be only 

 checked by the presence of rocky barriers and the diminishing depth of the water 

 of the river, aided perhaps by the increasing lowness of the temperature of the latter. 

 Although this Cetacean does not collect in herds, several individuals may often 



