376 



M. R. Thorpe — Arceocyon. 



such as Hycenognathus Merriam, Borophagus Cope, Chas- 

 maporthetes Hay, and so on. It is hardly probable that 

 any true hysenids will be found in North America and it 

 seems that these hyamid forms may be due to convergence. 

 Let us, however, compare one of these genera, for 



Major Characters. 



Hycenognathus pachyodon. 1 



2. 



6. 



' ' Mandible short and mas- 

 sive. ' ' 



" Alveolar margins great- 

 ly flared below P 3 and 



Dentition I 3 , C lf P 3 , M 3 . 

 "P 2 and P 3 small." 

 "P 4 very large, conical, 

 without accessory tu- 

 bercles. ' ' 



Mi massive 



protoconid 

 and paraconid forming 

 a heavy shear, meta- 

 conid absent; heel 

 short, with reduced hy- 

 poconid and e n t o c o- 

 nid." (Heel b as in- 

 shaped.) 



7. "M 2 and M 3 small." 



8. P x lost. 



9. Premolars crowded. 



10. Incisors spaced and none 



in front of canine. 



11. Symphysis long. 



12. M 2 and M 3 set in ascend- 



ing ramus. 



13. Muzzle much wider. 



14- Quaternary, probably. 

 Asphalto, Kern Co., 

 Calif. 



Arceocyon marshi. 



1. Mandible moderately long 



and slender. 



2. Alveolar margins but very 



slightly flared below P 4 . 



3. Dentition I 2 , C^ P 2 , M 2 . 



4. P 2 and P 3 absent. 



5. P 4 relatively smaller, com- 



pressed, with prominent 

 posterior tubercle and 

 heel. 



6. Mj, very large; protoconid 



robust ; paraconid large 

 and high ; metaconid 

 prominent ; heel large 

 with low hypoconid me- 

 dially situated on talonid. 

 (Heel trenchant.) 



7. M 2 long and stout. No M 3 . 



8. P x present. 



9. Long diastema between Pj 



and P 4 . 



10. Incisors crowded and outer- 



most one in front of ca- 

 nine. 



11. Symphysis short. 



12. M 2 placed nearly level with 



respect to tooth-row. 



13. Muzzle much narrower. 



14. Middle Pliocene. Near Cot- 



tonwood, East Fork of 

 John Day River, Ore. 



1 Merriam, J. C, The Pliocene and Quaternary Canidse of the Great Valley 

 of California. Univ. Calif. Pub., Bull. Dept. Geology, 3, 278 ff. with plates 

 and figures, 1903. 



