62 CETACEANS. 



union between the two branches of the lower jaw, which exceeds one-quarter the 

 total length of the jaw. The teeth vary in number from twenty to twenty-five on 

 each side of the jaws ; and are of rather large size, with the crowns often marked 

 by vertical groovings. The colour is variable. 



The rough-toothed dolphin attains a length of 8J feet; and takes its name 

 from its coarsely-fluted teeth. The colour of the upper-parts is purplish black, the 

 sides being marked with rather large star-shaped spots, and the snout and under- 

 parts white, tinged with purple and rose-colour, and ornamented with purple spots. 

 The plumbeous dolphin (S. plumbeus) of the Indian Ocean, has an extremely long 



THE ROUGH-TOOTHED DOLl'lilN. 



(From True. Bulletin of the U.S. National Museum, 1889.) 



beak, and is of a uniform leaden-grey colour, with the exception of the extremity 

 and under surface of the lower jaw, which are white. A third species from the 

 Indian seas is the speckled dolphin (S. lentiginosus), which above is of a leaden- 

 grey colour, with numerous long, drop-shaped spots, most of which are pure white, 

 but others slaty or black ; while below it is white, more or less mottled with grey. 



LONG-BEAKED RIVER-DOLPHINS. 

 Genus Sotalia. 



Under the above title may be included several species of dolphins closely allied 

 to those of the preceding genus, but distinguished by their fluviatile or estuarine 

 habits, and the smaller number of joints in the backbone. Their teeth are always 

 smooth ; and the flippers very broad at the base. They must not be confounded 

 with the fresh- water dolphins of the family Platanistidce. 



Amazonian Dolphins of this group are abundant in the upper portions of the 



Dolphins. Amazon, but there is still great uncertainty as to whether these 

 belong to one or to three species, or whether all or any of these are distinct from 

 the Brazilian dolphin (Sotalia brasiliensis) of the bay of Rio de Janeiro. There 

 is also a closely allied form (S. guianensis) from Cayenne. Of the Amazonian 

 dolphins one is commonly known as the tucuxi ($. tucuxi), a second as the pale 

 river-dolphin (S. pallida), and a third as (S. fluviatilis), which differ chiefly in 

 coloration, the relative length of the fins, and the number of teeth. The pale 

 dolphin, which is figured in the accompanying illustration, has the upper-parts and 

 flukes yellowish white, and the under-parts and flippers white. A notice of some of 

 the habits of the tucuxi has been given above on p. 39. 



