NO. 5 TELESCOPING OF THE CETACEAN SKULL 47 



Iniidcc. — There has been much difference of opinion as to the sys- 

 tematic position of Inia and its alhes, though they have, perhaps, 

 been most frequently united with Platanista and Stenodelphis to form 

 a special family. The unnaturalness of this grouping has been recog- 

 nized by Abel, True and Rovereto. The genus Platanista is widely 

 separated from the others by the physeteroid character of its tele- 

 scoping (compare pi. 6, fig. 2, with pi. 7, fig. 2) and by the exces- 

 sively specialized structure of its palatine and pterygoid. The South 

 American Stenodelphis^ though less distinct from the iniids than 

 from Platanista, is definitely separated from both Inia and Lipotes 

 by the structure of its palate (it agrees with them in type of tele- 

 scoping). This leaves these two existing genera and their extinct 

 allies tO' stand alone. Considered as a group they resemble the Del- 

 phinidce in the type of telescoping and in some other characters of the 

 skull. The braincase, however, has not attained its extreme size, and 

 has not encroached on the temporal fossa so much as in the typical 

 modern dolphins, peculiarities which suggest the squalodonts. A 

 character which might be interpreted as vaguely squalodont is also 

 indicated by the tendency of the posterior teeth to differ in form from 

 those at the anterior end of the series ; but the broadened teeth of 

 Inia obviously resemble the tuberculate teeth of Delphinodon rather 

 than the narrow trenchant posterior teeth of Squalodon. The struc- 

 ture of the palate is less specialized than in any of the known toothed 

 cetacea except the physeteroids and agorophiids. (The more im- 

 portant characters of the palate in the squalodonts, it must be remem- 

 bered, are not known.) The narial passage has become perpendicular, 

 and the palatine bone has lost its primitive position on the roof of the 

 palate ; the orbits are situated in front of the level of the nares ; narial 

 process of palatine well developed and forming an important part 

 of the anterior wall of the narial passage. Pterygoid simple, not 

 spreading laterally over alisphenoid, and not reduplicated along either 

 margin. Posterior orifice of infraorbital canal apparently formed by 

 maxillary alone. A peculiar specialization is seen in the presence 

 of a narrow, freely projecting plate given off by the posterior ex- 

 tremity of the maxillary and extending back nearly to the squamosal 

 in somewhat the same position as that which is occupied by the outer 

 reduplication of the pterygoid in such delphinids as Delphinap tents 

 and Stenodelphis. In addition to the living genera Inia and Lipotes, 

 I would regard as probably members of this group the fossils which 

 have formed the bases of the following names : Anisodelphis, Argyro- 

 cetu^ (perhaps better referred to the Stenodelphinince) , Ischyrorhyn- 



