PLATE CLX 



Jaws of Brontops sp. and of Megacerops riggsi 



Plate prepared under the direction of Professor Cope. One-third natural size. (See p. 550) 



A', A^, Jaw referred to Brontops? sp. (Am. Mus. 6345b), Horsetail Creek, northeastern Colorado, Chadron formation. Incomplete 



lower jaw, seen from below and from the inner side; placed b}' Cope with the skull of "Symborodon bucco" (see PI. CLIII) 



but probably pertaining to a different genus and species. 

 B, Megacerops riggsi, type (Am. Mus. 63G4), Horsetail Creek, northeastern Colorado, Chadron formation. (See also Pis. CLVIII 



and CLIX.) This type lower jaw, seen from above, shows a short, thick symphysis, a short premolar series, and molars with 



external cingula obsolete — characters we should expect to find in Megacerops. 



