ART. 19 A MIOCENE PORPOISE FROM MARYLAND KELLOGG 15 



The walls of the brain case were too thin to withstand crushing and 

 the supraoccipital bone fractured in many directions. It also 

 buckled backward above the foramen magnum, and the amount of 

 crushing or displacement above the center of the upper margin of 

 this foramen may equal 15 mm. The posterior face of this fossil 

 skull resembles that of Sotalia tucuxl more closely than that of 

 Delphinodon dividum^ but differs from both in that the transverse 

 crest of the supraoccipital is essentially three-sided, the median strip 

 (25 mm.) being coextensive with the vertex at the rear, and each of 

 the lateral strips (46 mm.), which form an obtuse angle with the 

 median strip, are nearly twice as long. In Sotalia tuciixi the trans- 

 verse crest of the supraoccipital is essentially two-sided, with the 

 apex behind the median suture between the frontals. 



The supraoccipital is wider than high, more or less hexagonal in 

 outline, but is without a median carina on the upper portion; each 

 lateral lambdoid crest, a continuation of the transverse crest, follows 

 the natural curvature of the posterior end of the temporal fossa. 

 Along the posteroinferior border of the temporal fossa the lambdoid 

 crest overhangs the exoccipital as in Sotalia tucuxi. 



On the second skull (pi. 3, fig. 1) the paroccipital processes are 

 prolonged downward at least 12 mm. below the level of the inferior 

 borders of the falcate processes. Reversed conditions are found on 

 the skull of Sotalia tucuxi where the falcate processes project below 

 the paroccipital processes. In Sotalia the external margin of the 

 exoccipital is almost vertical, the ventral angle is blunt and rounded 

 off, and the jugular incisure is broad. Although the outer margin 

 of the exoccipital is incomplete on both sides of this fossil skull, it is 

 evident that it is truncated obliquely, the ventral angle curves in- 

 ward, and the jugular incisure is deep and narrow. The exoccipitals 

 do not completely conceal the squamosals from the rear. 



The foramen magnum is slightly higher than wide. Each oc- 

 cipital condyle is considerably broader near the middle than near 

 the top and tapers rapidly to the lower extremity. The internal 

 margins of the condyles are concave and are sharply defined; the 

 external margins are set off from the surrounding bone by a con- 

 tinuous shallow depression. The articular surface of each condyle 

 curves moderately from end to end and slopes forward from internal 

 to external margin. 



Lateral view. — Aside from a slender rostrum and a small brain 

 case, the skull as viewed from the side (pi. 5, fig. 1) is characterized 

 by a more or less rectangular zygomatic process, a large orbit, and 

 the presence of at least 40 slender teeth in each jaw, of which 32 are 

 lodged in the maxilla and 8 in the premaxilla. A tooth much larger 

 than the others projects forward and slightly downward from the 



