4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 87 



mally, the floor of the mesorostral gutter is contributed by the pre- 

 maxillaries and the vomer. 



The apex of the mesethmoid rises to the level of the dorsal sur- 

 faces of the premaxillaries. The mesethmoid sheathes the dorsal and 

 lateral faces of the presphenoid and thus forms a partition between 

 the narial passages superiorly, fills in the frontal fontanelle, and pro- 

 vides support for the nasals, and also for the vertex of the skull. The 

 anterior narrowing of the narial passages is correlated with the 

 distal enlargement of the presphenoid. Notwithstanding the hori- 

 zontal expansion of the premaxillaries, most of the anterior end of 

 the presphenoid is exposed. The presphenoid is the porous bone that 

 forms a plug across the proximal end of the mesorostral gutter, but 

 does not rise to the level of the premaxillaries above. 



The frontals are largely hidden from a dorsal view, being over- 

 spread by the premaxillaries and maxillaries laterally and by the 

 nasals medially. Posteriorly the frontals abut against the supra- 

 occipital on the vertex and it is barely possible that a very narrow 

 strip of these bones may have been exposed between the hinder ends 

 of the nasals and the missing dorsal crest of the supraoccipital. 



The elongated nasals are relatively large (35 x 16.5 mm.) and are 

 placed on the vertex between the posterior extremities of the pre- 

 maxillaries, but do not overhang the narial passages. The anterior 

 border of each nasal is bevelled off oblicjuely. The hinder ends of the 

 nasal bones are unusually thick (pi. 3). Behind the right nasal and 

 nearly in the midline, there is a small wedge-shaped bone which may 

 be either an exposed portion of the right frontal or a fortuitous divi- 

 sion of the right nasal. 



Lateral viczv- — Aside from the relatively large size of the brain- 

 case, the skull (pi. 2) is characterized by a rather high temporal fossa 

 which is partially roofed over by the maxillary and the underlying 

 lateral extension of the frontal, a fairly wide orbit, and a long zygo- 

 matic process. The rostrum is somewhat depressed proximally and 

 compressed from side to side anteriorly. 



The orbit is strongly convex, the outer margin of the supraorbital 

 process of the frontal being thickened, while the superimposed plate 

 of the maxillary is thin and shelving. The preorbital portion of the 

 supraorbital process of the frontal is rounded, while the postorbital 

 angle is almost trihedral. The small lacrimal is closely appressed to 

 the preorbital angle of the supraorbital process and its inner end is 

 mortised into the under surface of the maxillary. The jugal is a very 

 slender bone whose anterior end is ankylosed with the lacrimal below 



