A. With a tubercle occupying the entrance of the valley
between the lobes of the last upper molar. _U. robustum._
B. No tubercle at the entrance of the valley.
(_a_) Nasals divided by a deep groove; slender zygomatic
arch; dorsal vertebræ compressed. _U. Leidianum._
(_b_) No nasal groove; stout zygomatic arch; dorsal
vertebræ sub-cylindrical _U. princeps._