8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8/ 



ity is formed. Internal to the glenoid fossa and on the ventral sur- 

 face of the squamosal there is a longitudinal depression, deeper 

 posteriorly than anteriorly. This depression commences at the base 

 of the inner face of the postglenoid process and extends forward to 

 the anterior or temporal margin of the squamosal. The ventral por- 

 tion of the squamosal, internal to this last-mentioned fossa, is pro- 

 longed downward and inward to form a thin plate which, when com- 

 plete, is suturally united with the external reduplication of the 

 pterygoid. 



The paroccipital process is relatively thick, its ventral aspect is 

 roughened, and internally in conjunction with the descending plate 

 of the basioccipital an incisure is formed for the passage of the so- 

 called jugular leash and associated nerves. 



REMARKS 



Porpoises with long slender rostra predominated in the pelagic 

 faunas of the Lower Miocene, as is evidenced by the occurrence of 

 Argyrocctus in Patagonia, and ZipliiodclpJiis, Schizodelphis Y = Cyrto- 

 dclpJiis], Eoplafanista, and Acrodelphis in Italy. The two last- 

 mentioned genera are sufficiently distinct from the California skull 

 to eliminate them from further consideration. 



Although the proportions of this skull (PI. i) and the relations 

 of the bones constituting the dorsal surface are strongly suggestive, 

 at first glance, of Eurhinodelphis longirostris^ from the Upper Mio- 

 cene Anversian stage of the Antwerp Basin, Belgium, there are some 

 well-marked differences. The skull from California has a smaller 

 orbit, a longer and more slender zygomatic process, a relatively 

 greater transverse diameter at the level of the preorbital angles of 

 the supraorbital processes, the zygomatic width is somewhat less, the 

 hinder extremities of the premaxillaries are greatly thickened and 

 are applied to the lateral surfaces of the elongate nasals, the supra- 

 occipital shield is strongly concave, and the occipital condyles are less 

 protuberant. The nasals are missing on the type skull of E. lon- 

 girostris (No. 3249, Mus. Roy. Hist. Nat. Belgique, Bruxelles) and 

 the elements marked A^ on Abel's plate (1902, PI. 11) are actually 

 the frontals, into which the nasals were mortised. It is certain, how- 

 ever, that E. longirostris has much wider nasals than the California 

 porpoise. The braincase of Argyrocetns joaquinensis is somewhat 



^ Abel, O., Les dauphins longirostres du Bolderien (Miocene superieur) des 

 environs d'Anvers. Pt. II. Mem. Mus. Roy. Hist. Nat. Belgique, Bruxelles, 

 vol. 2, pi. II, 1902. 



