U. S. GEOLOGICAL StrKVET 



MONOGRAPH 55 PLATE XVII 



THE REGION OF THE HORN SWELLING IN MANTEOCERAS, MESATIRHINUS, AND DOLICHORHINUS 

 Manteoceras manteoceras (Am. Mus. 23S3), lateral view, left side (right side reversed). B, DoUchorhinus hyognathus (Am. 

 Mus. 1851), lateral view, left side (right side reversed). C, Mesatirhinus petersoni (Am. Mus. 1556), lateral view, left side. 

 D, DoUchorhinus hyognathus (Am. Mus. 1851), superior view. c. i. o. /., c. i. o., Infraorbital foramen; /r, frontal; h, rudi- 

 mentary horn; la, lacrimal; mo, molar; mx, maxillary; na, nasal; or, orbit; s. nar., external narial aperture 



