104 PROCEEDINGS OF THE NATIONAL MUSEUM vol. i05 



(Case, 1904, pp. 26-27, pi. 16) chiefly in the shghtly larger dimen- 

 sions. The St. Marys porpoise has slightly longer and more elevated 

 nasal bones, a narrower vertex, and a more deeply depressed maxil- 

 lary on each side of the vertex. 



Dorsal view: The skull (pi. 1) of this porpoise differs markedly 

 from those of all porpoises previously described from the Calvert 

 formation. Some resemblance to Diochotichus vanbenedeni (Moreno, 

 1892, pi. 11; True, 1910, pi. 1) and Squalodelphis fabianii (Dal Piaz, 

 1916) is exhibited by this skull, but it can be distinguished readily 

 from the former by the absence of a pair of foramina for the olfactory 

 nerves on the posterior wall of the nasal passages, by the elongated 

 vertex composed of the nasal bones and the exposed posterointernal 

 angles of the frontals, by the absence of any pronounced thickening 

 of the supraorbital processes and the overlying maxillary plates, by 

 the shape of the relatively slender zygomatic processes, and by the 

 greater number of teeth. 



The form of the rostrum is somewhat similar to that of Sgualodon 

 (Kellogg, 1923, pi. 1), the widest portion being at the level of the 

 antorbital notches. The lateral swelling at the base of the rostrum 

 extends forward for a distance of about 70 mm. beyond the antorbital 

 notches. In an interval of 130 mm. the rostrum diminishes in width 

 from 105 mm. to 48 mm.; the attenuation of the slightly longer 

 terminal portion of the rostrum is more gradual. The narrow antor- 

 bital notches are bounded externally by the lachrymal and by the 

 preorbital apophysis of the overlying maxillary. 



The premaxillaries are more or less flattened on the basal portion of 

 the rostrum, but become more convex anterior to the level of the 

 hinder end of the tooth row. Near the distal end of the rostrum, the 

 outer surface of each premaxillary slopes steeply from the inner to 

 the outer margin. The inner margins of the opposite premaxillaries 

 seem to have been in contact for a distance of about 20 mm. in front 

 of the nasal passages, and after spreading slightly apart gradually con- 

 verge at a point 150 mm. distant and then, closely approximated, 

 parallel one anotjicr to the extremity of the rostrum. The convex 

 portion of each premaxillary commences to widen transversely at 

 about the level of the antorbital notches and attains its maximum 

 width on the rostrum at about the level of the penultimate alveola. 

 Behind the level of the antorbital notches, the premaxillaries exhibit 

 the maximum transverse expansion in front of the nasal passages. 

 Opposite the nasal passages each premaxOlary is noticeably elevated 

 above the corresponding maxillary, the convex outer portion sloping 

 to the line of sutural contact with the latter. The posterior end of 

 each premaxillary is upturned, forming an oblique crest, and is 



