108 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 105 



strongly depressed behind the level of the nasal passages and there is 

 also a concave depression on each behind the level of the center of the 

 orbit. Although the outer border of the ascending plates of both 

 maxillaries are incomplete, there is no indication from the curvature of 

 the portions preserved that these plates were bent upward externally 

 as in the case of Inia. Two large and one small foramina, that 

 connect with the infraorbital system, are present in each maxillary at 

 about the level of the antorbital notches. 



From a dorsal view the frontals are largely concealed by the over- 

 spreading ascending plates of the maxUlaries, the slender posterior 

 ends of the premaxillaries, and the nasals. They are suturally united 

 posteriorly with the supraoccipital. Medially, the opposite frontals 

 meet edge to edge on the vertex, constituting a subscutiform area with 

 apex forward. The vertex is elevated, relatively small in area, 

 quadrangular in outline, and is constituted posteriorly by the postero- 

 internal angles of the frontals and anteriorly by the nasals. Laterally, 

 each frontal sends out a thin platelike extension which underlies at 

 least in part the horizontally expanded ascending plate of the maxU- 

 lary. Further forward, this portion of the frontal is considerably 

 thickened to form a complete osseous roof for the orbit. 



The nasals are rather large and irregular in shape; they constitute 

 the upper portion of the posterior wall of the nasal passages. Dorsally, 

 the nasals are deeply excavated internally, the surface of each sloping 

 obliquely dowmvard from the rounded outer border to the midline. 

 Anteriorly, the posteroexternal angle of each is prolonged forward. 

 The vertical diameter of the right nasal near the anterior end is 

 22.5 mm. 



Lateral view; Aside from the rather robust rostrum and the 

 relatively low vertex, the skull as viewed from the side (pi. 2, fig. 1) 

 is characterized by a relatively small braincase, by the small orbit, 

 by the laterally flattened and upwardly curved zygomatic process, 

 and by the presence of 26 to 27 robust teeth in each upper jaw, of 

 which 3 are lodged in the premaxillary. A tooth slightly larger than 

 the others projects forward and downward from the extremity of the 

 premaxillary. In Inia geqffrensis, the anteriormost tooth in the 

 premaxillary is almost vertical. At the base the depth of the rostrum 

 is approximately one half the corresponding width. For approxi- 

 mately 30 mm. in front of the antorbital notch, the ventral surface 

 of the maxillary slopes downward and backward from the outer 

 margin, and the upper surface slopes from the premaxillary-maxillary 

 suture to the outer edge. The basal swelling on the dorsal surface of 

 the maxillary that extends forward about 70 mm. in front of the 

 antorbital notch is rather strongly convex. Beyond this basal section, 



