314 University of California Publications in Geology [Vol. 13 



situated beneath the anterior root of M T in the preserved portion of 

 the lower jaw. 



Tig. 3. Peratherium merriami, n. sp. Left ramus, no. 24240, Mus. Palae. 

 Coll., lateral view, X 2. John Day beds, Logan Butte, Oregon. 



The dentition present in specimen 24240 includes the two posterior 

 premolars and the four molars of the upper jaw and comparable 

 teeth of the lower jaw. The two posterior premolars of the upper 

 jaw are laterally compressed, but relatively not so much as the 

 posterior premolars of Peratherium fugax. Each premolar possesses 

 a single prominent cusp. In both of the teeth a small ledge is situated 

 anterior to the principal cusp and a more extensive ledge is present 

 behind. A furrow or concavity is plainly visible along the inner 

 posterior side of the principal cusp in the last premolar. This furrow 

 is not so distinct in the preceding tooth. 



In superior molars 1 to 3 inclusive, M 1 possesses the shortest trans- 

 verse diameter. M 1 and ]\P have broad crowns while the crown of 

 M- is relatively narrow anteroposteriorly. 



Fig. 4. Peratherium merriami, n. sp. Superior cheek-tooth series, no. 24240, 

 Mus. Palae. Coll., lateral and occlusal views, X 4. John Day beds, Logan Butte, 

 Oregon. 



In M> the metacone is larger than the paracone. At least four 

 distinct elevations or stylar cusps are situated on the outer cingulum 

 of the tooth. The most anterior cuspule of the four is located at the 

 antero-external angle of the tooth. A ledge extends from the cuspule 

 along the anterior base of the paracone. The second stylar cusp is 

 more prominent than the first and is situated near the middle of the 

 outer base of the paracone. These two elevations or cuspules are 

 comparable to the a and b stylar cusps noted by Bensley 3 for the genus 



s Bensley, B. A., The homologies of the stylar cusps in the upper molars of 

 the Didelphyidae, Univ. Toronto Studies, Biol. Ser., no. 5, pp. 149-159, 1906. 



