8 PEOCEEDINGS OF THE NATIONAL MUSEUM vol.60 



position and extent of the glenoid articular surface on the zygomatic 

 l^rocess, the relative lengths of the upper and lower jaws, and the 

 differences in the shape and proportions of the teeth. As a rule the 

 progressive types of porpoises possess more simplified teeth and have 

 a shorter and more compact cervical series than the generalized 

 types. The cervical series is relatively short in both Delphinodon 

 dividum and Kentriodon pernix, and the centra are short and flat. 

 In case of Delphinodon dividum, the teeth are relatively large, with 

 rugose enamel on the crown, and accessory cusps on the posterior 

 ones; Kentriodon pernix^ on the other hand, has slender teeth, with 

 smooth enamel on the crown, but no accessory cusps were noted on 

 any of the teeth. 



Aside from a narrower brain case and a more slender rostrum, the 

 skull of Kentriodon pernix differs from that of Delphinodon 

 dividum'^ in having approximately 40 teeth in the upper jaw and 38 

 in the lower whereas in D. dividum there are not more than 27 teeth 

 in the upper jaw and 26 in the lower. With regard to the propor- 

 tions and relations of the bones on the top of the brain case, the skull 

 of Kentriodon peimix appears to agree more closely with the skull of 

 Acrodelphis (Phocaenopsis) scheynensis (Du Bus) figured by Abel ^ 

 than with any other Upper Miocene porpoise known to the writer. 

 The skulls of Kentriodon and Acrodelphis resemble each other in 

 the shape and proportions of the vertex, the form of the nasal bones, 

 the relative size of the posterointernal angle of the frontal exposed 

 on the vertex, the interval which separates the posterointernal angles 

 of the cranial plates of the maxillae, the relations between the pos- 

 terior extremities of the premaxillae and the nasal bones, and the 

 curvature of the transverse crest of the supraoccipital. There are 

 features, however, which indicate that these two fossil porpoises 

 represent different tjq^es and of these the peculiarities of the pre- 

 maxilla, particularly the greater width of this bone at the level of 

 the antorbital notch in A. scheynensis^ are the most obvious. If 

 Phocaenopsis scheyiiensis actually belongs in the genus Acrodelphis, 

 then Kentriodon also differs from that porpoise in the shape of the 

 mandibles and the length of the symphysis. 



The skull of Kentriodon pernix is of approximately the same size 

 and the dental formula is similar to Delphinavus neiDhalli^ but Pro- 



' True, F. W., Description of a new fossil porpoise of the genus Delphinodon from the 

 Miocene formation of Maryland. Journ. Acad. Nat. Sci. Philadelphia, ser. 2, vol. 15, pp. 

 165-194, pis. 17-26. December 9, 1912. 



* Abel, O., Les odontoc^tes du Bold^rien (Miocene supSrieur) d'Anvers. M6m. Mas. 

 Roy. d'Hist. Nat. de Belgique, Bruxelles, vol. 8, p. 135, text fig. 20 and p. 137, text flg. 

 21. 1905. 



» Lull, R. S., Fossil dolphin from California. Amer. Journ. Sci., New Haven, vol. 37, 

 pp. 209-220, text figs. 1-7, pi. 8. March, 1914. 



