THE PORPOISES AND DOLPHINS 1213 



the skeleton the breastbone is long and composed of two distinct pieces. This 

 species does not attain a greater length than five feet, and in some respects serves to 

 connect the other members of the family with those of the one following. 



The remains of a number of extinct dolphins have been discovered 



in the Tertiary deposits of various parts of the world, which appear 

 Dolphins . 



more or less closely related to the existing members of this family. 



Among these, two species from Argentine, respectively named Pontistes and Sauro- 

 delphis, approach the living Stenodelphis; while a third {Argyrodelphis} from 

 Patagonia is noteworthy from having the nasal bones well developed and roofing 

 over the hinder part of the nasal cavity in the manner characteristic of whalebone 

 whales. More remarkable, however, is the occurrence of another nearly-allied form 

 (Iniopsis*) in the Tertiary of the Caucasus, which serves to confirm the view that the 

 Platanistidce were a very ancient and widely-distributed family. Numerous other 

 extinct dolphins, some of which approach those of the next family, have been de- 

 scribed from North America and Europe, and referred to the present group. 



THE PORPOISES AND DOLPHINS 

 Family 



The whole of the remaining members of the existing Cetacea, including those com- 

 monly known as narwhals, porpoises, grampuses, and dolphins, are referred to a single 



SKELETON OF DOLPHIN. 



family, which contains a far greater number of species than any of the others. All 

 the members of this family are of small or medium size, and with the exception of 

 the narwhal and Risso's dolphin, are furnished with a numerous series of teeth in 

 both the upper and lower jaws, the jaws themselves being either elongated or short. 

 They are distinguished from the preceding family by the union between the two 

 branches of the lower jaw being always considerably less than half the entire length 

 of the jaw itself, and likewise by the manner in which the ribs are articulated to the 

 backbone, as well as by certain features in the base of the skull. The vertebrae of 

 the neck are generally characterized by the first two, three, or four being united. 

 The blowhole is always in the form of a transversely-placed crescent, with its two 

 horns directed forward. 



The majority of the dolphins (as it is convenient to term collectively 



the whole of the members of the family) are of marine habits, but 



many of them frequent estuaries and ascend tidal rivers, while a few are more or 



