250 



University of California Publications. 



[Geology 



evident close relationship to these forms it may be classed with 

 them until more material is obtained. 



Occurrence: Thousand Creek Beds; locality 1103, Thousand 

 Creek, Humboldt County, Nevada. 



Measurements 



No. 12541 No. 12540 



Height of mandible below protoconid of M x 4.3 mm. 3.4 



Mj, anteroposterior diameter 5.8 5.1 



M,, transverse diameter 2.5 2. 



Mj, anteroposterior diameter of heel 2.1 1.6 



M,, anteroposterior diameter of alveolus 1.5 1.4 t 



MUSTELID( ?), indet. 



The posterior half of a lower jaw (no. 12555, figs. 23a and 

 236) lacking the teeth and the coronoid process possibly repre- 

 sents a large mustelid form. The inferior margin of the man- 

 dible is more strongly convex below the anterior region of the 

 masseteric fossa than in most of the existing mustelids, but ap- 

 proximates the form in Potamotherium lacota in this respect. 

 The angle is broad and much flattened inferiorly, and approaches 

 the condyle very closely. The masseteric fossa is short and deep. 

 The dental foramen is situated only a short distance below a line 

 connecting the posterior margin of the alveolus of the last molar 

 and the inferior border of the condyle. 



The alveoli of two molars are present. The posterior tooth 

 was two-rooted and situated slightly transverse to the antero- 

 posterior axis of the jaw. The posterior portion of this tooth 

 rested partly on a distinct inwardly projecting prominence of 

 the alveolar margin which extends well behind the anterior bor- 

 der of the coronoid process. On the second tooth from the pos- 

 terior end of the inferior series the posterior root was circular 

 in cross-section and considerably flared above. The anterior 

 root is narrowed anteroposteriorly, and stands transverse to the 

 long axis of the jaw. The form of the anterior root of this tooth 

 is not that below the ordinary cutting blade on the trigonid 

 region of Mj in most carnivores. Either this alveolus represents 

 the anterior root of a M 2 , in which case M 3 would also be two- 



