CEEATOPSIAN DINOSAURS FROM MONTANA — GILMORE b 



presence of a nasal horn. The internal surface is smooth, with well- 

 defined longitudinal grooves that mark the course of nares superiorly. 

 On the underside at the posterior end the left nasal displays part of 

 the strongly grooved sutural surface for union with the frontal. This 

 end is slightly incomplete. 



An incomplete right maxillary containing five posterior teeth is 

 illustrated in figure 3. Most of the borders are incomplete except 

 for the concave posterior border, which has a vertically striated 

 sutural surface for the articulation of tlie ectopterygoid, and a short 

 median portion of the upper border, which probably articulated with 

 the premaxillary. In Protoceratops tlie pterygoid is said to articu- 

 late with this posterior border, no mention being made of the 



FiGUEB 3.- 



-Right maxillary of Lcptoceratops sp. (U.S.N. M. No. 13863) : Lateral view. 

 Qj Anterior end ; p, posterior end. Nine-tenths natural size. 



ectopterygoid. In Triceratops, however, as shown by Hatcher,* it is 

 the ectopterygoid that unites with this border. It is quite possible 

 that the ectopterygoid is fused with the pterygoid in Protoceratops 

 and was not recognized as a separate element. 



A fragmentary bone containing the simple roots of two teeth is 

 identified as the dentigerous border of the premaxillary. Measured 

 from center to center these roots are 8 mm. apart, showing the pre- 

 maxillary teeth to be more widely spaced than in Protoceratops. 



No recognizable parts of the frill portion of the skull were found. 



Teeth. — The few teeth present except for being slightly smaller are 

 in accord with those of Lcptoceratops gracilis. The roots are simple, 

 not bifid as in the Ceratopsidae. The fully adult teeth that have not 



« U. S. Geol. Surv. Monoar. 49. d. 26. fl£t. 21. 1007 



