38o THE SUSU CHAP. 



Tursiops. It has no dorsal fin, the teetli are small and numerous 

 (forty-four), and the pterygoids are separate. There are two 

 species, T. horealis and T. 2^eronii, the former being northern and 

 the latter more widely spread. 



The genus Ccphalorhynclius has for its chief characters tlie 

 following: — Teeth twenty-five to thirty-one, small and sharp. 

 Pterygoids widely separated. Dorsal tin not falcate, but tri- 

 angular or ovate in form. Beak not well marked off from the 

 head. The species of tliis genus are all soutliern in range ; four 

 are perhaps to l)e allowed. 



Fam. 3. Platanistidae, — This family of Odontocetes may be 

 distinguished from tlie Dolphins by tlie following assemblage of 

 structural features : — Cervical vertebrae all free, and eacli one of 

 some length (for a Cetacean). Jaws long and narrow, with a 

 considerable length of sympliysis. Teeth very numerous. 



This very meagre series of differential characters is largely due 

 to Pontopoi^ia on the Platanistid side, and to Monodon and 

 Belphinapterus upon the Delpliinid side. Otherwise tlie family 

 Platanistidae would Ije extremely distinct. The two last-named 

 genera have separate cervical vertebrae, and in tlie Beluga at any 

 rate this is expressed externally by a quite distinct neck. 

 Moreover, as Mr. True has pointed out, the pterygoid bones have 

 not the involuted cavity below whiclr cliaracterises other 

 Dolphins ; and tliey have, what other Dolphins have not, an 

 articulation outwards witli the roofing bones of the skull. Sir 

 W. Flower described tlie fact tliat in Liia (and tlie same occurs 

 in Fontoporia) the palatines are separated from each otlier by the 

 intervention of the vomer. In this feature they resemble certain 

 Ziphioids, BeranUus, Oulodon ( = Mcsoplodon) grayi, and Hypcro- 

 odon. The true Dolphins also appear to show the same inter- 

 vention of the vomer in a few cases. There is nothing, therefore, 

 distinctive from the Delphinidae in this feature. 



The existence of cartilaginous sternal ribs in Inia and 

 riatanlsta shows affinity lietween these two genera and tlie 

 Physeteridae. Pontoporla is Dolphin-like in this particular, as 

 it is also in the mode of articulation of the ribs with the verte- 

 bral column. But this last matter has already been dealt with. 

 The principal reason for placing Pontopjoria with the other two 

 genera is the close resemblance wliich its skull bears to that of Inid. 



The first genus of this family which will be noticed is Platanista. 



