286 



University of California Publications. 



[Geology 



ward, and tilted upward at an angle between twenty-five and thirty degrees 

 from the plane of the frontals above the orbits. Horn-cores flattened in 

 a plane extending backward and inward from the orbits. A short distance 

 above the base the horn-cores flare or widen slightly in the direction of 

 greatest diameter in cross-section. Outer anterior edge of the horn-core 

 arising over the upper posterior region of the orbit, and swinging back- 

 ward with a suggestion of a twist. Surface of the horn-core comparatively 

 smooth, with a few pits or irregularities. Texture of the outer portion of 

 the horn-core solid. Supraorbital formamina present in front of the 

 middle of the antero-medial side of the base of the horn-cores.'' 



Horn-core. — In the collections which have been examined 

 since the original description of this species a number of frag- 

 mentary specimens 

 have been obtained 

 which represent this 

 form. One of these, 

 no. 12537, represents 

 the base of a horn- 

 core (figs. 67a and 

 676), which is wider 

 anteroposteriorly, but 

 much thinner trans- 

 versely than the type 

 specimen. It also dif- 

 fers somewhat from 

 the type in the nature 

 of the region on the posterior side of the base' of the horn-core. * 

 In the type-specimen, this region is very broadly rounded or 

 nearly flat transversely. In no. 12537 the posterior basal region 

 is relatively much narrower, and a low longitudinal keel is de- 

 veloped on the middle of the posterior surface. 



In this specimen the tendency of the horn-core to flare 

 anteroposteriorly a short distance above the base is more dis- 

 tinctly shown than in the type material. This is possibly due in 

 part to the slightly better preservation of the anterior margin 

 in this specimen. Though the differences between this specimen 

 and the type of S. ncvadanus are considerable, it quite certainly 

 represents the same general group and may be referred to this 

 species. 



In the thinness of the horn and in the tendency to develop a 



67a 



Figs. 67a and 67b. Sphenophalos nevadanus 

 Merriam. Basal region of horn. No. 12537, 

 X V->. Thousand Creek Beds, Thousand Creek, 

 Nevada. Fig. 67«, medial side of horn; fig. 

 67b, cross-section of horn. 



