8 



University of California Publications. 



[Geology 



All the premolars excepting the first are represented in both 

 jaws. The presence of the anterior one is indicated in both cases 

 by a large alveolus. P 2 , P.., and P 4 have no anterior cusps or 

 tubercles, but all exhibit both a posterior cusp and posterior basal 

 tubercle. P 2 differs from all of the other premolars, excepting 

 the carnassial, in possessing a minute anterior cusp. P 3 shows 

 both a posterior cusp and a posterior basal tubercle. On the up- 

 per carnassial, a distinct notch on the anterior side of the proto- 

 cone separates a small cusp corresponding to the protostyle. The 

 deuterocone is small. 



The first upper molar is unusually broad on the lingual side, 

 though the posterior inner cusp or hypocone is not relatively 

 large. A well-developed metaconule is present, but there is ap- 

 parently no protoconule. The external cingulum is distinctly 

 marked. On M 2 the protocone is large and the metacone some- 

 what reduced. 



M x is not far from the stage of evolution seen in Canis, though 

 the metaconid is perhaps a little larger in Tephrocyon. On the 

 heel the low hypoconid and entoconid are distinctly separated. 

 The trigonid of M 2 is less reduced than in Canis, and possesses a 

 small paraconid. The heel of this tooth is not markedly different 

 from that of Can is. The hypoconid is a distinct but low tubercle. 



On M 3 there is a faint external ridge with three smaller ridges 

 running toward the inner margin. These elevations seem to rep- 

 resent the hypoconid and the three elements of the trigonid. 



Affinities. — This form seems to be generically separable from 

 the canids thus far described from the Miocene of America, but 

 it shows affinities with Canis, and to a certain extent with Aelu- 

 rodon. 



In the Canidae, the development of a protostyle on P 4 is a. 

 characteristic of the Aelurodons and Simocyon, though occurring 

 occasionally in other forms. In its incipient form it is present 

 rarely in modern species of Canis, particularly in the milk car- 

 nassial. In order to determine the degree of variability existing 

 in wild canid species, Dr. C. Hart Merriam and Mr. Vernon 

 Bailey have recently examined a large series of skulls in the col- 

 lections of the Biological Survey. The following results I quote 

 from a statement by Dr. Merriam. 



