PLATE CLVIII 



Jaws of Megaceeops eiggsi and Menodus torvus 

 Plate prepared under the direction of Professor Cope. One-third natural size. (See pp. 527, 550) 



A, Megacerops riggsi, type (Am. Mus. 6364), Horsetail Creek, northeastern Colorado, Chadron formation. This jaw was referred 



by Cope to "Symborodon acer" but seems far too small to pertain to that species. It is in fact extremely small for an OUgocene 

 titanothere. (See measurements, p. 242.) Reasons for referring it to Megacerops are the extremely short, thick horizontal 

 ramus, low ascending ramus and coronoid, very short symphysis and premolars, molars with obsolete external cingula — 

 characters which one would expect to find in the jaw of Megacerops. 



B, Undetermined jaw fragment referred by Cope to "S. bucco." (See PI. CLIII.) 



C, Menodus {"Symborodon") tonus, type (Am. Mus. 6365), Horsetail Creek, northeastern Colorado, Chadron formation. This 



jaw is the genotype of Symborodon (see p. 210), Cope's original description of the genus having been based upon this jaw, 

 although in his subsequent descriptions he erroneously included other material (jaws and skuUs) belonging to other genera. 

 The jaw seems to belong in the genus Menodus, as indicated by its general contour, measurements, absence of lower incisors, 

 and robust external cingula on molars. The skulls which Cope referred to "Symborodon" appear not to be congeneric with 

 this jaw but to pertain to Leidy's Megacerops. 



