ADDENDUM A. 
THE CRANIAL AND DENTAL CHARACTERS OF GEOMYHXaS. 
[Reprinted, with some modification, from the Bulletin of the United States 
Geological and Geographical Survey of the Territories, 2d series, No. 2, 
pp. 81-90, published May 11, 1875.] 
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In its massiveness and angularity, the skull of the Geomyidce differs alto 
gether from that of the Saccomyidce, in which the cranium is singularly papery 
and bullous, with few angles; and it quite closely resembles an' arvicoline 
type. The jaws are remarkably strong ; the incisors immense ; the zygomata 
flaring ; the occipital region is extensive ; the palate proper is contracted and 
at the same time prolonged downward ; there is a long arched interval between 
molars and incisors. On a plane surface, the skull without the lower jaw rests 
level upon the molars and incisors^ no other points touching the support. 
The molars are all rootless and perennial. The inferior incisors traverse the 
whole jaw. The superior incisors are semicircular. No anteorbital foramen 
occupies a usual site. The complex temporal bone is inordinately enlarged 
in all its elements, but especially the squamosal, which represents most of 
the cerebral roofing at expense of the reduced parietals. The malar is merely 
a short splint; there is an osseous tubular meatus auditorius. There are no 
orbital processes ; the interorbital constriction is narrower than the rostrum ; 
the latter is more than a third of the length of the whole skull. Such are 
some of the general features, from which we may proceed to details first 
of configuration of the whole, afterward of characters of individual bones. 
Viewed from above, rather less than the posterior two-thirds of the skull 
presents a subquadrilateral figure, from which the rostrum protrudes in front. 
The greatest width is opposite the fore part of the zygomata in most cases ; 
