352 University of California Publications in Geology [Vol. 12 



Comparative Tooth Measurements 





Eden, 

 No. 23369 

 Prosthennops 

 edensis, n. sp. 



Thousand 



Creek, 

 No. 2744 



Rattlesnake, 

 No. 3060 



F-, greatest anteroposterior diameter 



9.5' mm. 



10.9 mm. 



12 mm. 



P-, greatest transverse diameter 



9 



11.2 



9.6 



greatest anteroposterior diameter 



13 



12.4 



12.7 



Pi, greatest transverse diameter 



10.5 



12.6 



11 



Ml, greatest anteroposterior diameter 



13 





14 



M.-, greatest transverse diameter 



11.5 





11.7 



M2, greatest anteroposterior diameter 



16.6 







M-, greatest transverse diameter 



15 







Comparisons. — The teeth are larger and more bunodont than those 

 of a Prosthe7inops-like form from the Rattlesnake^^ that furthermore 

 shows certain Platygonus characters in the height of the crown, 

 tendency to more marked separation of the anterior and posterior 

 crests, and triangularity of the P- (Univ. Calif. Coll. Vert. Pal. no. 

 3060). 



The generally greater length of the cheek-tooth row and the more 

 progressive stage evidenced in the complete molariform character of 

 the la.st premolar, both in size and shape, are in contrast to the more 

 primitive Prosthennops crassigenis of the South Dakota Upper Mio- 

 cene, as illustrated and described by Dr. W. D. Matthews,^" "Premolars 

 much smaller than the molars ; . . . P- and P- four-rooted, but not 

 completely molariform . . " 



Prosihennops-\\^Q specimens of P- and P- from Thousand Creek 

 differ from the Eden forms in the presence of posterior and lateral 

 cingula in P- and a posterior accessory tubercle in both P- and P-; 

 also in the absence of the anterior shelf-like cingula seen in the Eden 

 species. The Thousand Creek specimen (Univ. Calif. Coll. Vert. Pal. 

 no. 2744'). furthermore, shows a certain advance over the Eden form 

 in the even greater development of the molariform P-. 



Upper jaw referred material. — Upper cheek tooth, Univ. Calif. 

 Coll. Verl. Pal. no. 23777 (fig. 61) is of premolar form. The pattern 

 is too worn to permit a specific determination, the four tubercles being 

 replaced by an irregular confluent depression, embraced by higher 

 and more resistant enamel of the unworn reentrant valleys and tooth 

 margin. There is evidence of a cingulum anteriorly and at the middle 

 of the inner side of the tooth. The specimen measures 11 x 6.5 mm. 



38 From unpublished manuscript, by courtesy of Professor John C. Merriam. 



39 Matthew, W. D., and Gidley, J. W. New and Little Known Mammals from 

 the Miocene of South Dakota. Amer. Museum Expedition of 1903. Bull. Am. 

 Mus. Nat. Hist., vol. 20, p. 265, 1904. 



