110 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 105 



was at least twice that of the orbit. Superiorly, the temporal fossa 

 is bounded by the thin platelike lateral extension of the frontal that 

 underlies the platelike ascending process of the maxillary; and pre- 

 sumably posteriorly the temporal fossa is bounded by the lambdoid 

 crest that follows the lateral margin of the supraoccipital. In this 

 fossa, the parietal is united anteriorly and superiorly with the frontal, 

 posteriorly with the supraoccipital, and inferiorly with the squamosal. 

 There is no evidence that the parietal participated in the formation 

 of the vertex. 



As compared with that of Inia geoffrensis, the laterally flattened 

 zygomatic process is shorter and less robust; it is thickened dorso- 

 ventrally and its anterior extremity is obliquely truncated. The 

 ventral margin is regularly curved and the postglenoid process is 

 relatively short. The greatest length of the left zygomatic process on 

 its articular face is 81 mm. and the greatest depth at its anterior ex- 

 tremity is 28 mm. 



Ventral view: The ventral surface of the rostrum (pi. 3) is formed 

 mainly by the maxillae, which meet mesially at the level of the 

 anterior margins of the palatines and continue forward in contact for 

 a distance of 60 mm. and then for an interval of 75 mm. are separated 

 by the axial ridge of the vomer. Behind the level of the 10th alveolae 

 counting backward from the first, the maxillae increase in width 

 markedly toward the antorbital notches, the palatal surface becoming 

 increasingly convex. The ventral orifice of the infraorbital canal is 

 located in the maxilla internal to the inner end of the lachrymal. 

 There were 24 teeth in the right maxilla, 23 in the left maxilla, and 3 

 in each premaxilla. 



On each side of the palate the presence of a thin groove, com- 

 mencing at the level of the anterior end of the ventral axial ridge of 

 the vomer and extending forward to the fourth alveola counting back- 

 ward from the first, suggests that a narrow strip of each premaxilla, 

 6 mm. in width anteriorly and 4 mm, posteriorly, may have separated 

 the maxillae on the distal portion of the rostrum. 



The dorsoventrally flattened lachrymal is wedged in against the 

 maxilla and the supraorbital process of the frontal and is partially 

 overspread ventrally by a thin plate of the latter. Ventrally, the 

 lachrymal externally and the jugal internally contribute to the 

 formation of the antorbital notch. 



The basal portion of the jugal on the left side is preserved, and it 

 is so intimately ankylosed to the large lachrymal bone that the 

 exact limits of these two bones cannot be determined. The slender 

 styliform process of the left jugal, however, was not found. 



