ENDOCRANIAL ANATOMY OF FOSSIL MAMMALS 345 
endocranial cast of Nothosaurus only suggests the form of the 
brain. Similar results have been obtained by other writers on 
ancient reptilian endocranial casts. 
A review of the literature on ancient mammalian endocranial 
casts will not be made here. All additional literature which has 
appeared since my annotated bibliography (’15) was printed has 
been given by Black (15, ’20). 
MATERIALS 
The nineteen endocranial casts are all from the White River 
Beds of South Dakota, ranging from Lower to Middle Oligocene. 
The casts represent the following forms: 
1 cast representing a primitive rodent, genus and species 
uncertain, possible a sciuromorph (figs. 1 and 2). 3 casts repre- 
senting primitive insectivores, Ictops acutidens (figs. 5 to 8). 
1 cast representing a primitive saber-toothed cat, Dinictis 
felina Leidy (figs. 3 and 4). 
1 cast representing an undetermined felid, possibly Hop- 
lophoneus (figs. 9 to 11). 
1 cast representing a primitive bear-dog, Daphaenus felinus 
Leidy (fig. 12). 
8 casts representing the common oreodont, Oreodon (Mery- 
coidodon) culbertsoni Leidy (figs. 22 to 28). 
1 cast representing a species of Merycochoerus, a large semi- 
aquatic oreodont, associated with casts of the paranasal sinuses 
Gage 17); 
1 cast of Oreodon gracilis Leidy associated with paranasal 
sinus casts (fig. 21). 
1 cast doubtfully representing Oreodon gracilis Leidy (figs. 18 
to 20). 
1 partial cerebral cast representing the three-toed horse, 
Mesohippus (fig. 24). 
I am obliged to Mr. Paul C. Miller, of the University of Chicago, 
Mr. E. S. Riggs, of Field Museum, and Mr. H. T. Martin, of 
the University of Kansas, for the loan of material. For aid in 
confirming the identification of the casts I am endebted to 
Mr. E. S. Riggs, Dr. W. D. Matthew, and Dr. E. L. Troxell. 
