1902.] Mattheiv, A Horned Rodent from Colorado Miocene. 307 



external one on m^, and a posterior one on m^. The median 

 crescent is somewhat less persistent than the internal inflec- 

 tion. Enamel is lacking on the external side of the teeth 

 except in very young animals. 



The internal inflection is that which has become deeper and 

 more persistent in Lepus; the crescent has disappeared in 

 modern species of Lepus, and in the John Day L. eiinisiaiius 

 apparently does not persist as long as in PalcBolagus. The 

 enamel fails on the external side of the upper teeth of Lepus 

 except for a little while after they are protruded. 



Dr. Forsyth-Major has suggested that the second upper in- 

 cisor of the Lagomorpha has originated from the posterior cusp 

 of such a tooth as that of Plesiadapis ; the bifanged tooth 

 splitting in two and the large anterior cusp giving rise to the 

 large incisor of the modern lagomorph. Palceolagiis, he thinks, 

 might help to verify this theory. But the incisors of PalcBolagns 

 are quite of modern type. It is to the lower Eocene Rodentia, 

 including the Mixodectidae, or to the as yet little-known fauna 

 of the Cretaceous, that we must look for light on the method 

 of evolution of their teeth. But Eocene Lagomorpha have 

 not yet been discovered. 



Palceolagiis approaches most nearly to Forsyth-Major's 

 Caprolagns group among modern Leporidae. These species 

 are less specialized for speed, and in consequence the head is 

 carried lower and more forward, and the basicranial and basi- 

 facial axes are at a smaller angle. 



Angle between basifacial and basicranial axes in different 

 species of Palceolagus and Lepus. 



P. agapetilliis 7° 



P. intermedius 20° 



P. haydeni 22° 



L. ennisianus 7,7,° 



L. campestris 47° 



Palaeolagus ? agapetillus Cope. 



Professor Cope held this species as distinct in 1874, but in 

 1884 united it with P. haydeni. A skull found by our party 



