80 



THE CERATOPSIA 



one on the part of the latter. The form of the squamosals has high diagnostic value in other 

 ceratopsians. But perhaps the most striking contrast lies in the very large parietal fenestrae in 

 Protoceratops, so large that there is merely a narrow band of bone between them and the rear of 



Fig. 34. — Lateral view of anterior cervicals of 

 Protoceratofs anirewsi, No. 6417 A.M.N.H., J4 

 natural size.- az, anterior zygapophysis of fourth 

 cervical; h, capitular facet; if, intervertebral fora- 

 men; fz, posterior zygapophysis of fourth cervical; 

 s, neural spine of axis; /, neural spine of third cervi- 

 cal; s", neural spine of fourth cervical; t, tubercular 

 facet. 



AMNH 5464 



Fig. 3 5. — Lateral view of anterior cervicals of 

 Leftoceratofs, J4 natural size, h, capitular facet; 

 if, intervertebral foramen; fz, posterior zygapophysis 

 of fourth cervical; r, rib; s, neural spine of axis; 

 /, neural spine of third cervical; s" , neural spine of 

 fourth cervical. 



the crest. The rather large portion of the Leftoceratofs parietal preserved shows no trace of fenestrae 

 at all, so that if fenestrae shall ultimately be found in Leptoceratops, they will be much smaller and 

 farther forward, for the area where they occur in Protoceratops is here solid bone. This one element 

 is so distinctive that, however closely allied these forms may prove to be on other counts, their dis- 



Fig. 36. — Right pubis of Protoceratofs andrewsi, 

 No. 6417 A.M.N.H., internal view, y 2 natural size. 

 f, pubis; ff, postpubis. 



Fig. 37. — Right pubis of Leftoceratofs, internal 

 view, J4 natural size, f, pubis; ff, postpubis. 



tinction is surely generic. The general form of the skulls was probably quite different, as the much 

 longer nasals in Leptoceratops give further evidence. 



Of the anterior cervicals, all are thoroughly coossified in Leptoceratops (Fig. 35), while in 

 the unmounted skeleton of Protoceratops (Fig. 34), No. 641 7 A.M.N.H., the atlas and axis are fully 

 fused, the axis and third cervical are coossified at the base of the centrum, but the zygapophyses are 

 distinct. The spine of the axis is erect in both genera and not bent backward as in all other cera- 

 topsians. The caudal vertebrae are similar in the two genera, but otherwise unique among horned 



