U. S. GEOLOGICAL SURVEY 



MONOGRAPH 55 PLATE CLXXXIV 



(See pp. 

 n gigas? 

 Occiput 



SKULLS OF BRONTOTHERIUM GIGAS AND B. CURTUM 



Plate prepared under the diredlion of Professor Marsh. One-sixth natural size 

 568, 575, also Pis. CLXXV and CXXXIX.) A, Skull referred to Brontotheri 

 (Yale Mus. 12061?), South Dakota, Chadron fonnation, probably upper levels 

 of type skull of Titanops elatus Marsh? As compared with B. curtum, the occiput 

 narrow and the depression for the ligamentum nuchae is less extensive. B, BrontO' 

 therium curtum, type (Yale Mus. 12013), Colorado, Chadron forxaation, upper beds 

 (Hatcher). Occiput of type skull of Titanops curtus Marsh. The occiput is vi'ider, with 

 a deep insertion area for the ligamentum nuchae and widely flaring creels for the re<5tus 

 capitis lateralis muscles 



