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University of California Publications. 



[Geology 



connecting the anterior sides of the bases of the horns the frontals 

 slope backward and downward from the frontal plane anterior 

 to the horns at an angle of about sixty degrees. On those speci- 

 mens showing the portion of the frontal above the orbits the 

 supraorbital foramina (fig. 3) are situated a little behind the 

 middle of the superior side of the orbit, and just in front of the 

 middle of the base of the horn core. They vary from round to 

 long-elliptical in form. 



Fig. 8. — Ilingoeeros, sp. Frontal region with bases of horn cores. No. 

 11882. X%. 



The horn arises immediately above the upper posterior region 

 of the orbit (fig. 4), and the middle of its basal portion is situ- 

 ated almost immediately over the postorbital process of the 

 frontal. It slopes backward and slightly outward with a suffi- 

 cient upward tilt to make an angle of approximately twenty-five 

 degrees with the plane of the frontal above the orbits. In the 

 type specimen a low, rounded ridge which arises from the portion 

 of the horn core base nearest the orbit swings backward over the 

 outer side of the horn, twisting around it at the rate of one com- 

 plete turn in about three and one-half inches. This ridge grows 

 much stronger as it approaches the posterior side of the horn. 

 In the type specimen it is accompanied by a groove which arises 

 just above the postorbital process of the frontal. A second ridge 

 rises behind this grove so that two distinct spiral ridges are 

 present (fig. 1) . 



Excepting the notch formed by the groove between the two 

 principal ridges, the cross-section of the horn core in the type 

 specimen tends to be approximately circular, as it is also in a 

 fragment of a horn (no. 11886) quite certainly referable to this 

 species. Judging from the nearly uniform width at the two ends 



