4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



and on the ventral face of the skull extends inward beyond the infra- 

 orbital foramen. From a dorsal view^ it is triangular in outline and 

 is of approximately the same thickness as the frontal plate of the 

 maxilla. There is no preorbital process or apophysis. The distal 

 end of the jugal is present on both sides of this skull. This portion of 

 the jugal is subtriangular in outline and occupies a median position 

 in the maxillary notch. It is merely a small wedge which has forced 

 its way in between the maxilla and the lachrymal from both of which 

 it is separated by sutures. 



The nasal bones are about equal in length to the maximum breadth 

 between the premaxillae of the exposed portions of the frontals on 

 the vertex of the skull. In position, the nasals are considerably pos- 

 terior to those of Archaeo del phis ^ and probably are farther back than 

 those of Agorophhis, both nasals of which are missing. The anterior 

 margins of the nasal bones in the Xenorophus skull do not extend 

 beyond the middle of the supraorbital process. The nasals do not 

 completely roof over the nasal passages, and hence the anterior nares 

 open in almost the same direction as in Squalodon calvertensis. On 

 each side the nasals are bounded by the broad premaxilla. 



The frontals are much reduced in extent on the vertex, being over- 

 spread by the premaxillae laterally and by the nasals anteriorly. The 

 supraorbital process slopes forward ; its postero-external extremity 

 appears to be imperfect and probably curved downward. A close 

 examination of the posterior ends of the frontals does not reveal any 

 evidence for sutural union with the parietals at this level and the 

 surfaces correspond to similar fractures elsewhere on this skull. The 

 curvature of the sides of the skull in the temporal fossae, and the 

 narrowness of the frontals on the vertex is evidence that this skull 

 was characterized by a better marked intertemporal constriction than 

 in either Archaeodelphis or Agorophius. In both of these forms, 

 each parietal sends forward a median process which fits into a cor- 

 responding depression in the combined frontals. 



Lateral view. — The dorsal outline of the rostrum is almost straight 

 in front of the maxillary notches, but slopes downward toward the 

 extremity. As a whole the skull appears to have been rather slender, 

 and the height at the vertex is proportionately low in comparison with 

 that of the base of the rostrum. The crest-like ridge of the premaxilla 

 is the highest point of the dorsal profile anterior to the intertemporal 

 constriction. The alveolus for the last two-rooted tooth terminates 



^ Allen, G. M.. A new fossil cetacean. Bull. Mus. Comp. Zool. at Harvard 

 College, vol. 45, No. i, pi. i, fig. i, 1921. 



