172 



University of California Publications. 



[Geology 



stage of evolution of this species and of the associated Hyaenog- 

 nathus seems to show that they are probably not older than 

 Pliocene. 



The portion of the mandible present represents a large ani- 

 mal, and the species must have been one of the more formidable 

 members of the sabre-tooth group. The jaw is noticeably heavy, 

 while the inferior flange is wider and deeper than in the typ- 

 ical species of Smilodon and Machaerodus but hardly as prom- 

 inent as in Hoplophoneus, In the symphysial region the infer- 

 ior portion of the anterior face is concave on either side of 



Fig. 1. Machaerodus ( f ) ischyrus, n. sp. X%. 



the median line, but the whole upper part of this face is strongly 

 convex, and the portion of the alveolar margin occupied by 

 the incisors is bowed far forward. In the region of the cheek 

 teeth the alveolar margins are flared outward rather more than 

 is common in the cats, owing probably to shortness of the jaw. 



The dentition is o-. 



I 3 is absent from both rami, but 



its alveolus indicates the existence of a tooth approaching the 

 canine in size. I 2 is considerably larger than l v P 3 is very 

 small and is single-rooted. P 4 possesses a single large accessory 

 cusp on either side of the protocone, but shows no trace of a 

 posterior basal cusp. The protoconid stands almost erect. In 

 M. 1 the protoconid and paraconid are well developed and of 

 nearly equal size. The posterior portion of is somewhat 



