42 



University of California Publications. [Geology 



larger specimen. As in Arcliaelurus, P 2 is double-rooted and P 3 

 has a weak anterior basal tubercle. 



A third and much smaller mandible (No. 1683) shows the 

 weak exostosis of N. gomphodus and the double-rooted P 2 of 

 Arcliaelurus. The inferior portion of the jaw is broken away, 

 but the massateric fossa extends far forward as in A. debilis. In 

 this specimen the diastema, to P 2 , is very short and the median 

 portion of the inferior side of the symphyseal region is rather 

 prominent. The well-preserved M, is laterally compressed and 

 has a divided root. It shows a sub-acute superior ridge which is 

 divided into a median tubercle and distinct anterior and poste- 

 rior basal ridges. 



The relative dimensions of these individuals compared with 

 those of the described species of Arcliaelurus and Nimravus are 

 brought out in the following table : — 



Length of mandible, anterior 

 side of symphysis to poste- 



Height of mandible below mid- 



o 



I 



1= 



£> 

 X 



ebilis 



ho 



ho 



|H 



mfertus 



o 



ft g 





6 





6 



8 a 

 . a 



. pi 



te >> 



6 







* 





158 



al75 





140 







27 



31 





20 



20 



20 



31.5 



37 

 16 





24 

 14.5 



10 





23 



25 





21 



18.5 





17 



17 



15 



14 





13.3 



20 



19.5 





15 





16 



25 



27 



26 







22.5 



Height of mandible at poste- 

 rior end of P 4 



Length, posterior side of ca- 

 nine to anterior side of P 2 ~ 



Length, posterior side of ca- 

 nine to anterior side of P 3 .. 



Antero-posterior diameter of 



P 



Antero-posterior diameter of 



i\ 



Antero-posterior diameter of 



M, 



a Approximate. 



The mandibles described above correspond generically to 

 Arcliaelurus and differ from the two species of Nimravus in the 

 presence of P 2 and in the characters of the massateric fossa. In 

 the two specimens in which P 3 is present it supports an anterior 

 basal tubercle as in Arcliaelurus. In each individual, however, 

 some considerable deviation from the type of Arcliaelurus is seen, 

 and in all cases this variation is toward the type of Nimravus. 



