940 EOCENE AND OLIGOCENE TIT.VNOTHERES OF MONGOLIA 



sents a nearer resemblance to the American Man- ' , , , ,. , ^„^ ■'^'i'^tT^ 



, ,, , T ,• i r M2, ap. b}' tr. (index 50) 60X30 



teoceras, it probably represents a distmct genus of m,, ap. by tr. (index 40) 83X33 



titanotheres or of chalicotheres characterized by Transverse measurement of two inferior canine alveoli, 



procumbent lower canine teeth. outer sides 58 



Length of inferior symphysis, estimated 88 



Manteoceras? irdinensis Osborn, 1925 , Depth of symph3'sis from median point 36 



Original reference. — Osborn, H. F., Upper Eocene Specific characters. — (1) Symphysis of mandibular 



and lower Oligocene titanotheres of Mongolia: Am. ramus broad, shallow, flattened inferiorly, containing 



Mus. Novitates No. 202, 1925. alveoli for two enlarged semiprocumbent canines; 



Type locality and geologic level. — The type jaw (2) space occupied by premolars relatively reduced 



(Am. Mus. 20111) of Manteoceras? irdinensis is from (80 mm.), as in all titanotheres, pi apparently absent 



the Irdin Manha formation, 2 miles north of the or vestigial; (3) true grinders, mi-3, rapidly increasing 



Kalgan-Urga telegraph line. It includes the greater in anteroposterior diameter (190 mm.), a characteristic 



part of the right ramus, containing the three true titanotheroid feature; (4) faint sculpturing of the 



grinding teeth, mi-3. The premolar alveolar border , external cingula in the outer valleys only, extending 



Figure 794. — Type jaw (fragment) of Metarhinusf mongoliensis (Am. Mus. 20167), compared with 



Protitanotherium grangeri (Am. Mus. 20168) 

 Natural size. (Compare fig. 774, G). A, Superior and lateral aspects of fourth inferior premolar and of first inferior molar of MetarJiinusT 



mongoliensis (Am. Mus. 20167) from the Irdin Manha formation; B, lower jaw fragment, pi, mj, of Proiitanotherium grangeri (Am. 



Mus. 20168) from the Irdin Manha formation. 



is partly fractured, and it is difficult to determine the 

 number or form of the premolar teeth. A highly 

 distinctive character is the broad, flattened symphysis, 

 containing two very large alveoli, apparently for a 

 pair of approximated, procumbent canine teeth; the 

 enlarged canines leave only a narrow space for the in- 

 cisive border. The imperfect condition of the speci- 

 men prevents oirr determining the formula of the 

 cutting teeth. The principal characters in profile, 

 superior, and inferior views are clearly shown in the 

 type (fig. 793), in which the supposed outlines of the 

 premolar teeth are properly restored. 



Principal measurements of Manteoceras? irdinensis 



Millimeters 



Grinding series, ?P2-in3 270 



Premolar series 80 



Molar series 190 



Ml, ap. by tr. (index 64) 42X27 



over the outer lobes; (5) ramus deepening to 119 

 millimeters behind ma. The ramus, as preserved, is 400 

 millimeters long, being greatly inferior in proportions 

 and length to the ramus of ProtitanotTierium grangeri. 



SUBFAMILY DOLICHORHININAE 

 Metarhinus Osborn, 1908 



The fragmentary type jaw here described as 

 Metarhinus? mongoliensis (Am. Mus. 20167) certainly 

 represents a species of titanothere distinct from 

 any previously described from Mongolia in this 

 monograph, as it is separated from all others both 

 by its diminutive size and by the peculiar form of the 

 two lower grinding teeth preserved (p4?, mj). Com- 

 parison with all the known specimens of chalicotheres 

 and titanotheres of corresponding age shows that it 

 most nearly resembles the small titanothere known as 



