272 University of California Publications in Geology [Vol. 12 



ing feature of each of the specimens is the preservation of the pre- 

 fossette, thus presenting a very close similarity to C. occidentalis as 

 figured by Osborn. They are more like the corresponding teeth of the 

 latter species in their enamel pattern than they are like those of the 

 species of rhinoceroses from the Agate Spring quarry of- Nebraska. 



Regarding the evolution of premolar teeth in aceratheres, Professor 

 Osborn* has remarked: "The stages in the assumption of the molar 

 pattern by the premolars furnish the key to the Oligocene species of 

 Aceratheres, and are thus of great importance." In the changes of 

 crown shown by P- and P- the principal modification which takes place, 

 according to Osborn, is the opening inward of the prefossette to form 

 the valley between protoloph and metaloph. The teeth of the rhinoc- 

 eros from Teeuja Canon, when viewed in the light of the interpre- 

 tation of premolar evolution in Oligocene members of the group, exhibit 

 a stage of development possessed ratlier by Oligocene than by later 

 forms. 



Leidy"' lias described the species Rhinoceros hesperius from materials 

 collected in Tertiary deposits of Calaveras County, California, and 

 referred to him by J. D. Whitney. Teeth of tliis form, according to 

 Leidy, also approach closely in size the corresponding teeth of Caenopus 

 occidentalis. The fragmentary materials at present available do not 

 permit, however, a satisfactory comparison between the Tecuja and 

 Calaveras species. 



Measurements of No. 23614 



pi, greatest transverse diameter measured along posterior side 22 mm. 



pi, anteroposterior diameter a22.5 



P-?, greatest transverse diameter at base of crown a40 



P5, greatest anteroposterior diameter o31 



P-, height of crown measured over middle of outer side 25.5 



a, approximate. 



SCIURTD, sp. indet. 



This squirrel-like form is represented by specimen 23611 (fig. 6), a 

 fragmentary ramus of the mandible with only Mj and IMj preserved. 

 The material indicates a form somewhat larger and heavier than the 

 living CitcUus hcecheiji fishcri from the adjacent region of Fort Tejon. 

 In the fragment of fossil jaw the anterior border of the attachment 



■* Osborn, H. F., op. cit., p. 112, 1898. 



'< Leidv, J., The extinct mammalian fauna of Dakota and Nebraska, etc., 

 Jour. Acad. Nat. Sci. Phila., ser. 2, vol. 7, pp. 230-232, pi. 23, figs. 11-12, 1869. 



