ART. 19 A MIOCENE PORPOISE FEOM MARYLAND KELLOGG 



11 



Comparison of skiUls of Kentriodon permx and Delphinodon dividum Cope — 



Continued 



VENTRAL ASPECT — Continued 



Delphinodon dividum True 



Jugal small, ankylosed to lachrymal 

 posteriorly, and mortised into ven- 

 tral surface of maxilla internal to 

 antorbital notch; styliform process 

 noticeably enlarged as it approaches 

 body of jugal. 



Internal surface of each falcate process 

 of the basioccipital characterized by 

 an oblique ridge which extends from 

 near anterior margin to postero- 

 inferior angle. 



Zygomatic process and glenoid articu- 

 lar facet narrow, but the internal 

 margin is undercut and is set off 

 posteriorly by an excavation on ven- 

 tral surface of squamosal. 



Not more than 27 teeth on each side; 

 the largest teeth 29 mm. in length 

 and 5 mm. in diameter; the smallest 

 teeth 20 mm. in length and 4 mm. in 

 diameter. 



Crowns of teeth recurved, with rugose 

 enamel, and a distinct carina on 

 anterior and posterior cutting edges; 

 posterior teeth with one or more 

 accessory cusps; roots slender, gib- 

 bous below crown, and have a large 

 dentinal canal. 



Kentriodon pernix 



Jugal small, ankylosed to lachrymal 

 posteriorly, and mortised into ven- 

 tral surface of maxilla internal to 

 antorbital notch; styliform process 

 exceedingly slender, not enlarged as 

 it approaches body of jugal. 



Internal surface of each falcate process 

 of the basioccipital rather evenly eon- 

 vex, no ridge. 



Zygomatic process and glenoid articular 

 facet wider, and the internal margin 

 is strongly undercut and set off pos- 

 teriorly by an excavation on ventral 

 surface of squamosal. 



At least 40 teeth on each side, the ante- 

 rior one noticeably larger than others 

 and projects forward and downward 

 from extremity of premaxilla; the 

 largest teeth 38.3 mm. in length and 

 3.9 in diameter; the smallest teeth 13 

 mm. in length and 2.8 mm. in 

 diameter. 



Crowns of teeth recurved, with relatively 

 smooth enamel, but with neither 

 carinae nor accessory cusps; roots 

 slender, slightly enlarged below crown, 

 and have a small dentinal canal. 



Dorsal view. — As seen from the dorsal side the skull (pi. 2) of 

 this porpoise differs markedly from that of Delphinodon dividum; 

 the mo.st noticeable peculiarities are its long and attenuated instead 

 of rapidly tapering rostrum, less expanded premaxillae in the region 

 of the respiratory pas.sages, deeper antorbital notches, and narrower 

 cranium, although the horizontally expanded posterior extremities 

 of the maxillse are relatively wider. The form of the base of the 

 rostrum appears to be quite characteristic, since both skulls exhibit 

 the same peculiarities. In accordance with the usual method of 

 description the rostrum is considered to commence at the antorbital 

 notches which are bounded externally by the broad apophyses of the 

 maxillae. In front of the antorbital notches the exposed portions of 

 the maxillae are somewhat narrower than the premaxillae. The 

 premaxillae are more or less horizontal on the base of the rostrum, 



