16 PROCEEDINGS OF THE NATIONAL MUSEUM yol. 69 



extremity of the premaxilla. In Sotalia tucuxi, not more than 2 of 

 the anterior teeth are lodged in the premaxilla. Judging from these 

 two skulls some variation in the relative lengths of the rostra may be 

 expected inasmuch as the measurements show that in case of the first 

 skull (pi. 5, fig. 1) it is equivalent to about three-fifths of the total 

 length while in the second skull (pi. 5, fig. 2) it is almost three- 

 fourths of the total length. As regards relative depth the rostrum 

 agrees with that of Sotalia fucuxi. At the base the rostrum is about 

 two-thirds as deep as wide. For approximately 50 mm. in front 

 of the antorbital notch the outer border of each maxilla is rounded 

 off and the upper surface is flat and almost horizontal. Beyond this 

 basal section the slope of the upper surface of the maxilla is from 

 the premaxillary suture to the alveolar margin, becoming steeper 

 as the maxilla decreases in depth and near the extremity is almost 

 vertical. Near the middle of the rostrum the dorsolateral face of the 

 maxilla is deeper than the premaxilla, but from this point forward 

 it gradually diminishes in height while the premaxilla increases. 

 The extremity of the rostrum is formed entirely by the premaxillae. 

 From a lateral view the alveolar gutter is barely visible throughout 

 its length and on the right side terminates 16 to 18 mm. in advance 

 of the antorbital notch. The axis of the rostrum is approximately 

 horizontal and the basicranial axis is bent downward from that of 

 the rostrum. 



The anterior margins of the nasal bones are the highest points on 

 the dorsal profile; from these bones to and slightly beyond the 

 antorbital notches, the premaxillae slope strongly downward. The 

 maxillae, on the other hand, slope more gradually from the trans- 

 verse crest of the supraoccipital to the base of the rostrum. 



On its external border the supraorbital process of the frontal is 

 rather thin. The anterior angle or preorbital process is a slight en- 

 largement, about 14 mm. in depth, but the posterior angle or post- 

 orbital projection is prolonged downward, forming a slender pro- 

 jection which did not come in contact with the zygomatic process. 

 As a result of crushing in a dorsoventral direction, the postorbital 

 projection on the second slmll (pi. 5, fig. 2) was appressed to the 

 anterior face of the right zygomatic process, while the first skull 

 (pi. 5, fig. 1) was crushed in a more oblique direction and an in- 

 terval of 20 mm. separates the above-mentioned processes on the 

 right side. The maximum length of the right supraorbital process 

 of the first skull (Cat. No. 8060) is 59 mm. and that for the second 

 skull (Cat. No. 10670) is 60 mm. 



The large lachrymal bone is closely appressed to the anterior face 

 of the supraorbital process and is overspread above by the apophysis 

 of the maxilla. Below the antorbital notch the small wedgelike jugal 



