PORPOISES AND DOLPHINS 331 



Genus Steno. 



THE ROUGH-TOOTHED DOLPHIN {Steno rostratus). 

 Fig. 91. 



The species Steno rostratus may be taken as typical of a 

 group of long-beaked dolphins whose most obvious claim to 

 generic distinction is that the teeth, instead of being smooth 

 on the crown, are roughened or furrowed. 



The beak is long and, unlike that of the Common Dolphin, 

 passes without break into the 'forehead ', and it is distinguished 

 from the latter by the smaller number and greater size of the 

 teeth. From the Bottle-nosed Dolphin it is distinguished by 

 having the beak compressed rather than depressed, and by 

 having a much longer bony union of the two branches of the 

 lower jaw. 



The general body form is slender, very like that of the 

 Common Dolphin, which it resembles also in shape and size 

 of dorsal fin and flippers. 



Teeth number 20 to 27 on each side o f upper and lower 

 jaws and, being about § inch in diameter, compare in size 

 with those of the Bottle-nosed Dolphin. 



The upper surface of the body is slate coloured or purplish 

 black, with irregularly scattered star-shaped marks. Flippers, 

 flukes and dorsal fin are dark. The ventral surface of the 

 body is mainly pinkish white or rose colour, but speckled with 

 slate-coloured spots. The beak is white. 



The adult length is about 8 feet. 



This species is found in the warmer parts of the Atlantic 

 and in the Indian Ocean. In 1930 a specimen stranded on the 

 Biscay coast of France. 



Nothing is known concerning the habits of this animal. 



Several forms which may be distinct have been given specific 

 names, but they are of rare occurrence and need not concern 

 us here. 



Genus Prodelphinus. Fig. 92. 



What Cuvier said about the cetacea in general applies with 

 particular aptness to the two remaining imperfectly-known 

 genera of the Delphinidae to be described. In ' Le Regne 

 Animal ' he states : " II n'est point de famille de Mammiferes 



