Vol. 5] 



M err tarn . — John Day Carnivora. 



9 



"In the big Wolf, out of 107 skulls, a faint trace of a cusp 

 may be seen in 1 adult. 



"In Coyotes, out of 450 skulls, a faint trace exists in 3 adults, 

 and a distinct cusp is present in the milk tooth of 15 young. 



"In Canis (or Cerdoeyon) magellanicus, out of 22 skulls, no 

 trace of a cusp in the adult; a faint cusp is present in the milk 

 tooth of 2 out of 6 young. 



"In Red Foxes, out of 244 skulls, no trace in adult: slight 

 trace in milk tooth of 5 out of 10 young. 



"In Kit and Desert Foxes, out of 70 skulls, 2 adults show 

 trace of a cusp ; 9 young have a small cusp on the milk tooth in 

 each case. 



"In the Arctic Fox, out of 24 skulls, 1 adult shows a faint 

 trace, and 5 young in milk teeth show a faint trace. 



"In TJrocyon, out of 241 skulls, 2 adults and 3 young in milk 

 teeth show trace of a cusp ; other young show no trace. 



"It is probably an exaggeration to state that any of the adults 

 show a trace of the real protostyle." 



The cusp as it appeal's in T. rurestris is stronger than in any 

 variation of the recent Canis which I have seen, but it is much 

 weaker than in Aelurodon, and should hardly be termed a true 

 protostyle. This species also shows some resemblance to the 

 Aelurodons in M 1 and M 2 . It is distinguished from Aelurodon, 

 among other characters, by the very imperfect development of 

 the protostyle of P*, the less reduced metaconid of M A , the larger 

 M 2 , and the large inner lobe of M 1 . In most of the characters in 

 which it differs from Aelurodon, it approaches Canis. 



Tephrocyon differs from Canis in the structure of P 4 , M 2 , and 

 M.j, as indicated in the discussion of the dentition above. There 

 are also differences in the skvdl. The premaxillaries pass the an- 

 terior ends of the frontals, the sagittal crest is very prominent, 

 the otic bullae are extraordinarily large, and the mandible is 

 strongly convex below the posterior molars. 



The genus is more primitive than the typical Aelurodons in 

 the imperfect development of the protostyle of P 4 , and in the 

 larger metaconid of M,. It is more primitive than Canis in the 

 characters of M 2 and M... The anterior molars in both jaws are 

 near the stage of evolution seen in Canis. As the animal was a 



