143 



spine of tlic lliiid fcrvical vertcljra is applied. Tlic diapopliysis of this ver- 

 tebra has a short vertical articulating surface, and is continued into a longi- 

 tudinal keel, which disai)pears before reaching the edge of the cup. The 

 same process of the axis has a longitudinal parallelogranimic articular sur- 

 face. 



The supraoccipital is very thick, and is roof-shaped, the keel rising 

 nearly perpendicularly from the foramen magnum. The suspensoria are 

 directed both upward and backward, at about an angle of 45° in each direc- 

 tion, and support, on their extremities, the squamosal bones. These are pro- 

 longed, each forming a part of its appropriate arch. Tlie occipital condyle is 

 transversely oval. The sphenoid bone embraces, as usual, the basi-occipital 

 protuberances ; it is not carinate on the median line below. It sends out, on 

 each side near the anterior extremity, a subhorizontal, laminar process. 



The quadrate hone is much like that o{ P. ictericus, but is relatively 

 smaller. While the teeth in that species are smaller, the quadrate is larger; 

 hence, the difference in the species is, in this point, quite striking. The 

 internal angle is prominent, but very obtuse, and is the summit of a very 

 thick, obtuse ridge, which extends to near the distal articular face. Tbe 

 posterior hook is much prolonged downward, and has no buttonlike process 

 or extension of the articular surface on its posterior face. This face presents 

 a strong rib along the meatus, ahd, disappearing above the pit, throws the 

 latter into a depression. This is increased by the swelling of the internal 

 angular rib. A prominent knob, very rugose at the extremity, rises beneatli 

 the end of the hook, and bounds a concavity between it and the internal rib. 

 The latter closes the concavity by curving round toward the knob above 

 mentioned. A keel rises interior to the rib, and below it, and continues into 

 the internal angle of the articular extremity. Another very prominent keel 

 extends from the knob beneath the hook to the base of the great ala. The 

 articular extremity is transverse, and in one plane. 



The maxillarij bone is marked with shallow longitudinal grooves. It 

 supports eleven teeth, and has a rather steeply-descending premaxillary 

 suture in front. The nareal expansion in front occurs opposite the fourtli 

 tooth. 



The teeth are rather long, slender, and incurved and recurved. There is 

 a distinct cutting-edge anteriorly, and on a greater or less part of the length 

 of the posterior face. Tlio crowns are four or five faceted on the outer face: 



