SYSTEMATIC DESCRIPTION OF GENERA AND SPECIES 



The classification of the Ceratopsia, as modified from Williston, 1 may be stated as follows: 



Class — Reptilia 



Sub-class — Diapsida 



Super-order — Archosauria 

 Order — Ornithischia 

 Sub-order — Ceratopsia 



Family 1 — Protoceratopsidae 



Genera — Protoceratops, Leptoceratops 

 Family 2 — Ceratopsidae 



Genera — Anchiceratops, Arrhinoceratops, Brachyceratops, 

 Chasmosaurus, Ceratops, Eoceratops, Monoclo- 

 nius (Centrosaurus), Pentaceratops, Styracosau- 

 rus, TriceratopSy Torosaurus. 



Family PROTOCERATOPSIDAE Granger and Gregory 3 



The family characters are as follows:" primitive, small ceratopsians, with a hornless skull; with- 

 out secondary skull roof above the frontals; no epoccipital bones; well developed crest with sagittal 

 ridge and persistent parietal fenestrae; premaxillaries with teeth; cheek teeth arranged in a vertical 

 series of not more than two developed at one time, roots simple not bifid; fore limb slender, manus 

 much smaller and shorter than pes, the latter elongate with compressed unguals; ilium with blade 

 but slightly inclined outward to the sagittal plane, not reflected or produced laterally above the 

 femur; prepubic process relatively small, not expanded vertically; femur with large fourth 

 trochanter, femur shorter than tibia; midcaudal vertebrae with very long spines. 



Genus PROTOCERATOPS Granger and Gregory 3 



Protoceratops andrewsi Granger and Gregory 3 



Pis. I, IV; Text Figs. 32-34, 36 



Holotype: No. 6251, A.M.N.H., a skull, lacking the occiput. Much other material has subsequently been found, 

 consisting of several skeletons and no fewer than seventy-three skulls, ranging in age from the newly hatched 

 young to the senescent. 



Horizon: Cretaceous; Shamo series, Dja-doch-ta formation. 



Locality: On the Kwei-wa-ting trail, east of Artsa Bogdo, Gobi Desert, Mongolia (Lat. 44°N., Long. 104°E.) 



Collector: Walter Granger and party, Sept. 2, 1922. 



The original description is as follows: "The skull (A.M.N.H. No. 6251) is hornless and far 

 smaller than that of any known ceratopsian or ankylosaur, being only about 160 mm. in length 

 from the anterior end of the premaxilla to the posterior border of the jugal. As seen from above, 

 it is broadly triangular, with a pointed apex and wide lateral crests, the latter composed chiefly of 

 the backward-and-downwardly expanded jugals. The greatest width of the skull across the posterior 

 borders of the jugals is about 190 mm., while the depth of the jugal below the middle of the orbit 



1 Williston, S. W., 1925. 



2 Revised from Gregory and Mook, 1925, p. 4-. 



3 Granger, W., and Gregory, W. K., 1923, pp. 1-9. 



