332 WHALES AND DOLPHINS 



plus difficile a observer et dont les descriptions soient plus 

 incompletes et la synonymie plus vacilante que celle des 

 Cetacees." 



Very nearly allied to the genus Steno is Prodelphinus, which 

 is distinguished from that form, however, by the teeth being 

 smooth and the union of the two branches of the lower jaw 

 a short one. Again, Prodelphinus is distinguished from the 

 Common Dolphin by an osteological character. The palate in 

 the Common Dolphin is deeply grooved on the inner side of 

 the tooth row, but no such grooving is found in Prodelphinus. 

 It is seen, then, that it is necessary to use internal features to 

 distinguish this genus from those which it so closely resembles 

 in external appearance. 



In all members of the genus the beak is elongated and 

 narrow ; the dorsal fin and flippers are as in the Common 

 Dolphin, and in none of the species is coloration sufficiently 

 distinctive to make identification an easy matter. Teeth are 

 small, pointed and numerous, 37 to 52 pairs in each jaw. 



A host of species has been described, about none of which is 

 there very much information concerning habits. Many of 

 the forms are known only from skulls, but here we shall confine 

 description to the more noteworthy species of which there is 

 at least some account of external appearance. 



The Slender Dolphin, Prodelphinus attenuatus, is black 

 dorsally and blackish grey on the sides ; an oblique band of the 

 latter colour invades the dorsal blackness in the region of the 

 tail. The sides are speckled with little white spots. Teeth 

 number 35 to 44 in each side of upper and lower jaws and the 

 animal attains a length of 6 feet. It is found in the tropical 

 and sub-tropical parts of the Atlantic Ocean. 



Prodelphinus piagiodon occurs on the Atlantic coast of 

 North America from Cape Hatteras and the Gulf of Mexico. 

 It is described as " dark coloured upper half of the body and 

 the fins spotted with white or light grey ; light coloured lower 

 half of the body with oblong spots of dark grey ". Its length 

 is 7 feet and teeth number 34 to 37 in each series. 



The Bridled Dolphin, Prodelphinus froenatus, resembles the 

 last described, but is smaller in size, reaching a length of about 

 6 feet. It is found in the Atlantic and Indian Oceans. Teeth 

 number 37 or 38 in each jaw. 



