28 Field Museum of Natural History — Geology, Vol. IV. 



faced molars usually little worn in the adult and with no trace of a 

 hypocone in M 3 . The earlier forms of both phyla have high sagittal 

 crests. The expanding cranial areas in the more advanced forms 

 develop differences which become more and more evident. 



Metarhinus fluviatilis, Osborn.* Type of genus. 



Type specimen, No. 1500 Amer. Mus. 



Type locality, base of Metarhinus Beds, White River Canyon. f 

 This is much the smaller and more primitive species of the genus. 

 It may be readily distinguished by the small size (355x200 mm.), the 

 short basi-cranial region, the long sagittal crest and the prominent 

 hypocone on M 3 . No specimen referable to this species was secured by 

 the Field Museum. 



Metarhinus riparius, sp. nov. 



Type specimen, No. 12 186 Field Museum. (PI. VII, Fig. 1). 



Range: Entire Upper Metarhinus Beds, White River Canyon and 

 divide. 



Specific characters: Skull long and narrow (405x210 mm.). An- 

 terior cranial region expanded, sagittal crest short. Inter- 

 orbital region relatively narrow and rounded, rudimentary 

 horn-cores above orbits, canines large, molar series short (88-93 

 mm.), hypocone usually present on M 3 , mandible straight in the 

 ramus, lower canine long and recurved. 



This is the most common species in the Metarhinus Beds. Four 

 skulls, two associated lower jaws and one isolated, in the Field Museum 

 collections are referred to it. (Nos. 12174, 12183, 12191, 12195, 12196.) 



Metarhinus cristatus, sp. nov. 



Type specimen, No. 12194 Field Museum. (PI. IX, Fig. 3). 



Type locality: Upper Metarhinus Beds (Horizon A), White River 

 Canyon. 



Specific characters: Skull, length approximately 380 mm., molar 

 series 94 mm. Frontal region broad, sagittal crest long and 

 high, molars short-crowned, no hypocone on M 3 , arches rela- 

 tively heavy. Represented by a single skull lacking the nasals 

 and the premaxillaries. 



* Bull. Am. Mus., Vol. XXIV, p. 609, 1908. 

 f Fide Peterson. 



