Vol. 5] 



Merriam 



. — John Day Carnivora. 



43 



Specifically the individuals described above are not readily 

 fitted into any of the known groups. The largest specimen, No. 

 1679, exceeding both A. debilis and N. gomphodus in size, be- 

 longed to an individual slightly larger than that represented by 

 the skull No. 1681 described above (p. 39). These two specimens 

 probably represent the same species, which is possibly a variety 

 of A. debilis, or as suggested by the size and by the reduction of 

 the exostosis, it is perhaps a variant from the N. gomphodus type. 

 Until more is known of the variation in the group this form may 

 be tentatively known as Archaelurus debilis major. 



The slightly smaller mandible, No. 1680, corresponds closely 

 to N. gomphodus in size, and possesses only a rudimentary ex- 

 ostosis. As P 2 was present and P 3 has an anterior basal tubercle, 

 this specimen may be tentatively referred to A. debilis major. 



The third specimen, No. 1683, has nearly the same dimensions 

 as the type of A. debilis, and is referred to that species, though 

 as in N. gomphodus the inferior portion of the symphyseal re- 

 gion is prominent and the exostosis much reduced. 



The great variation in size and form of the exostosis among 

 these and other known specimens indicates that, as suspected by 

 Cope, this structure cannot be used in generic separation and 

 only doubtfully in distinction of the species. The value of the 

 anterior basal tubercle on P 3 in separating the genera must also 

 be doubtful, as the difference between the small anterior tubercle 

 in Archaelurus and the rather prominent anterior basal angle in 

 Nimravus is slight. The presence of P 2 in A. debilis is of doubt- 

 ful value as a distinguishing character. It is a very small and 

 practically functionless tooth, and its occurrence would naturally 

 be variable. "While it is usually present in specimens with the 

 A. debilis type of massateric fossa and showing an anterior basal 

 tubercle on P 3 , it is also associated with a posteriorly serrated 

 inferior canine and a greatly reduced exostosis. It is absent 

 from Professor Condon's specimen in which the superior pre- 

 molar dentition is that of Archaelurus. Practically the only 

 character which seems distinctive is found in the form and size 

 of the massateric fossa. In N. gomphodus its inferior margin is 

 separated from the lower border of the horizontal ramus by a 

 wide bar. In A. debilis the fossa extends farther forward and 



