NO. 8 INTERRELATIONSHIPS OF THE CETACEA VVINGE 2'] 



and become massive, with wrinkled enamel. In compensation, how- 

 ever, they have become less numerous and the most posterior in the 

 jaws have acquired a form which is anything but primitive : the base 

 of the crown is more or less tubercularly widened out inward. The 

 narrow palate is retained. The lateral margin of the facial depression 

 is considerably more upturned than in Pontoporia, and the posterior 

 border, especially in the median region formed by the frontal, is far 

 more elevated. 



Lipotes as compared with In'ia is surely the more primitive in the 

 greater slenderness of the teeth ; on the contrary it is the less primi- 

 tive in having the facial depression relatively strongly widened behind. 



Saurodelphis {Sanrocctus, Pontoplanodes), Tertiary, Argentinian, 

 known from most of the skull, appears to have also originated from 

 Pontoporia-like animals, but it has gone in another direction than 

 Inia. It has retained the slender face with the narrow palate, but the 

 number of teeth is reduced to about 20 in each jaw. At the same time 

 the teeth are enlarged ; in any event they have acquired roots that are 

 more widened antero-posteriorly ; this is especially true of a number 

 of the anterior teeth in each jaw. In these teeth the root appears to 

 be in process of dividing in two, so that in cross-section it is almost 

 8-shaped, a form which, especially as regards the anterior teeth, is 

 quite the opposite to primitive. The lateral margin of the facial de- 

 pression is trenchant and highly upraised, even more than in Inia. 

 The hinder margin of the depression is not only elevated in the middle 

 as in Inia, but is also pushed further back. 



Plafanisfa also probably traces its origin back to Pontoporia-Mke 

 creatures. It has gone further than any other member of the family 

 in the direction of making over the jaws into delicate forceps. The 

 face is so slender and the palate so narrowed that the right and left 

 toothrows in the upper jaw lie closely side by side; they may even, 

 especially at the extreme rear, where the teeth are undergoing 

 atrophy, be pushed into each other. Somewhat similar conditions 

 obtain in the lower jaw. The number of teeth is about 30 in each 

 jaw. Several teeth at the front of each jaw have acquired high, 

 pointed crown and compressed, enlarged root. The outer margin of 

 the facial depression has grown upward, higher than in any other 

 genus, especially that part of it which runs along the outer margin of 

 the maxillary over the orbit and front of the temporal fossa. This 

 part has shaped itself quite fantastically as a huge plate which rises 

 high upward and bends in over the posterior part of the face, which it 

 covers like a mask, since each plate nearly meets its fellow from the 



