348 ROY L. MOODIE 
So far as I can learn, the brain cast of no ancient rodent: has 
been previously described. 
Troxell (’21), in a recent study of material in the Yale Museum 
representing Paleolagus, with which this cast was compared, 
remarks that the brain of Paleolagus is relatively small and flat, 
differing from the present cast in length and breadth and in the 
small size of the foramen magnum. The small size of the brain 
is merely a substantiation of the law announced by Professor 
Marsh (’74), which he indicates in these words: ‘In other groups 
of mammals, likewise, so far as observed, the size of the brain 
shows a corresponding increase in the successive subdivisions 
of the Tertiary.” 
G. Elliot Smith (’02, p. 195) has called attention to an interpre- 
tation of the smoothness of the cortex of the brain of certain 
rodents which is pertinent here. Contrary to the usual assump- 
tion, he believes that the smoothness of the cortex, such as is 
exhibited by the endocranial cast of the ancient rodent, does not 
indicate a primitive condition of the cortex for the group. Some 
of the mammals, such as the hystricomorphine Rodentia, with 
cerebral hemispheres the same size as the beaver, possess numer- 
ous deep sulci. He states: ‘“This is one of the enigmas of cerebral 
morphology which we are utterly unable to satisfactorily explain 
at the present time.”’ 
Insectivora 
Ictops. The three cranial casts discussed under this heading 
are identified as Ictops by Doctor Matthew and Dr. E. L. 
Troxell and for the sake of convenience I have referred to them 
under the specific name Ictops acutidens, an insectivore of the 
White River, Oligocene, beds. There is no assurance that the 
casts represent this species, or even that the casts, found isolated 
as they were, belong to the same species. There is, however, a 
wide range of variability exhibited by the skeletal parts of Ictops. 
The family Leptictidae, representing the primitive hedgehogs, is 
an ancient group of this curious order of mammals, which Doctor 
Matthew regards as a group “defeated and disappearing in the 
struggle for existence.’’ In past time the Insectivora were of 
