LONG-BEAKED RIVER DOLPHINS 1235 



skull is very narrow and compressed; and also by the length of the bony union be- 

 tween the two branches of the lower jaw, which exceeds one-fourth 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 ver- 

 tical groovings. The color is variable. 



The rough-toothed dolphin attains a length of eight and one-half feet, and takes 

 its name from its coarsely -fluted teeth. The color 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 color, and ornamented with pur- 

 ple spots. The plumbeous dolphin (S. plumbeus) of the Indian Ocean, has an 

 extremely long beak, and is of a uniform leaden -gray color, with the exception of 

 the extremity and under surface of the lower jaw, which are white. A third spe- 

 cies from the Indian seas is the speckled dolphin (S. lentiginosus), which above is 



THE ROUGH-TOOTHED DOI.PHIN. 



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



of a leaden-gray color, 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 gray. 



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 Platani slides. 



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

 Amazonian . . ... 



Dolphins Amazon > but tliere ls stl11 g reat 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 dol- 

 phins one is commonly known as the tucuxi (S. tucuxi}, a second as the pale, river 

 dolphin (S. pallida), and a third as (S. flumatilis), which differ chiefly in 

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



