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University of California Publications in Geology [Vol. 11 



posterior end of M 1} whereas in the Ricardo specimen this fossa does 

 not reach farther forward than the posterior end of the alveolus of 

 M 3 . In the Ricardo mandible the last premolar and the carnassial 

 are larger than in the type of C.f ursinus, whereas M 2 is smaller, 

 and M 3 was presumably smaller judging from the alveolus. 



The Ricardo form represented in no. 22470 was evidently a type 

 with dentition specialized in a direction which gave relatively more 

 emphasis to function of P 4 and the carnassial, although the crushing 

 area of the molar series was large ; while in C. ? ursinus the use of the 

 crushing area of the tubercular molars was relatively more important. 



In the importance of P 4 with M 4 in the lower cheek-tooth series, 

 in the tendency to especial massiveness of P 4 , and to some extent in 

 the form of the posterior half of the mandible, the Ricardo jaw, 

 no. 22470, suggests the late Pliocene Hyaenognathus. The Ricardo 

 jaw is considerably longer than that of Hyaenognathus, but the most 

 marked difference is found in the more specialized form of P 4 of 

 Hyaenognathus. In the Ricardo specimen P 4 is apparently not 

 radically different from a heavy Canis or Aelurodon tooth of this 

 position. In Hyaenognathus P 4 is greatly broadened posteriorly, and 

 the principal cusp is extraordinarily enlarged. It is possible that 

 Hyaenognathus is derived from the group to which the Ricardo species 

 belonged. It may be noted that the upper dentition of A.f aphobus, 

 to which it has been suggested that the Ricardo mandible, no. 22470, 

 may be referred, is quite different from that of Hyaenognathus 

 {Porthocyon) dubius with which the mandible of the type of 

 Hyaenognathus has been compared. 



Comparative Measurements 



C ?. ursinus 



No. 22470 type 



Height of mandible below posterior end of Mj 44 mm. 45 



Length of dentition from anterior side of P 4 to pos- 

 terior side of M 2 73 a64.5 



P 4 , anteroposterior diameter 22.2 al7 



M„ anteroposterior diameter 36.5 31 



M,, anteroposterior diameter of heel o9 



M„ greatest transverse diameter of heel 13.7 



M s , anteroposterior diameter 15.8 20 



a, approximate. 



AELUEODON ?, n. sp. A 



A portion of a lower jaw, no. 21225 (figs. 146a, 1465), represents 

 a heavy-jawed canid of a type similar to Aelurodon wheelerianus of 

 the Barstow fauna but heavier, with much heavier and larger car- 



