PLATE CXVII 



Skulls of Allops serotinus 

 One-seventh natural size. (See pp. 515, 516, 517, also Pis. CXIX and CXX) 



A, Nat. Mus. 4251, skuU H, type. Big Badlands, S. Dak., Titanolherium zone, level C (J. B. Hatcher).' The horns are widely 



divergent, trihedral in basal section; the connecting crest lies in the posterior plane of the horns; the nasals are abbreviated 

 by the forward growth of the horns; the parietal region is narrow, the zygomatic expansion moderate, the skull top long, the 

 occiput produced backward. 



B, Am. Mus. 520, Cheyenne River, S. Dak., Chadron formation. A skull referred to A. serotinus in which the above-mentioned 



features are emphasized. 



C, Nat. Mus. 4938, skull j, Big Badlands, probably Indian Draw, S. Dak., Titanolherium zone, level middle C (J. B. Hatcher). A 



skull referred to A. serotinus. The horns and nasals are more massive than in the preceding specimen, and the parietal crest 

 is broader. 



D, Nat. Mus. 2151, skuU I, collection of 1886, Big Badlands, S. Dak., Chadron formation, level upper C, 80 feet above Pierre 



shale (J. B. Hatcher). Skull of a supposed female with small horns and slender zygomata, referred to A. serotinus. 



1 Hatcher says, "77 feet above Fort Pierre shale; 34 feet below base of Oreodon beds, allowing liberally for summit of Jitanolherium beds." Darton (in letter) gives 40.7 

 feet above Pierre shale for the same skull H. 



