370 
U. S. P. R. R. EXP. AND SURVEYS-ZOOLOGY-GENERAL REPORT. 
distinct from the squamous. They are of considerable extent, entering into the occipital sur¬ 
face, and very largely into the under part of the cranium. The meatus externus is broad and 
tubular, with thin walls, its axis projecting forwards, outwards, and upwards ; and it is 
embraced posteriorly by a thickened process of the squamous bone. 
The malar hone is very short; its posterior half is concealed from view from above by the 
process of the temporal ; anteriorly it is more or less enlarged, and fits into a notch of the 
zygomatic plate of the maxillary, which forms the whole anterior portion of the zygoma, and 
sends a thin plate backwards under the malar. Thus, in consequence of the forward projection 
of the temporal on the upper surface of the zygoma, and the backward projection of the maxil¬ 
lary on the under, the two points leave but a slight interval between them when the malar bone 
is removed. 
The bony palate of Geomys is much restricted, being really confined to a narrow space between 
the molars. This is convergent anteriorly, where it is not wider than the molars ; it is traversed 
by two deep grooves, leaving a central and two lateral ridges of nearly equal height; the central 
one is prolonged anteriorly to the incisive foramina. A plane tangent to the surface just described 
would show a considerable interval between it and the cranium or petrous bones behind, and a 
still greater one in front, the outline of the under surface of the bone rising rapidly from the 
molars to near the incisors, and then curving a little down again. The palatine surface here is 
narrow, the cross section being truncate wedge-shaped, the outline widening above. The inter¬ 
maxillary suture is seen on the side of the muzzle, about its middle ; just within it is seen a deep 
depression, at the bottom of which is the anterior termination of the ante-orbital foramen ; this, 
however, does not open through the bone into the nasal cavit) r , as in Dipodomys. The incisive 
foramina are entirely in the intermaxillaries. The zygomatic plate of the maxillary is broad and 
oblique, standing out in a plane perpendicular to the axis of the skull (the two of opposite sides 
being nearly in the same plane); it is nearly plane anteriorly; its lower margin rises rapidly from 
the alveoli of the molars to a point opposite the centre of the skull, and then curves somewhat 
downward again ; it is thickened superiorly with a flattened surface, which expands behind to 
receive in its notch the end of the malar. 
It has already been stated that the lower jaw is very massive ; much more so than in any 
other American rodents. There is scarcely any postero-inferior angle, this being represented by 
a compressed ridge posteriorly, commencing below the root of the last molar. The upper por¬ 
tion of this ridge turns off horizontally, however, and is continuous with a horizontal thickened 
process standing out perpendicularly to the side of the jaw ; this represents the upper corner 
of the postero-inferior angle. The lower outline of the jaw is a nearly equable and convex 
curve throughout, mostly parallel to the inferior surface of the incisor. The condyloid has 
scarcely any neck, although rather a deep notch separates it from the coronoid process, which 
rises considerably above the level of the condyle. There is a very deep pit below the base 
of the coronoid process, and exterior to the last molar. The covering of the posterior extremity 
of the lower incisor is seen as a very prominent tubercle (larger than the condyle) which is 
situated on the outside of the jaw, and at a height about midway between the condyle and the 
horizontal process already described. There is also an excavation or pit running along the out¬ 
side of the jaw, internal and anterior to this tubercle. 
The incisors, as already remarked, are of extraordinary strength and size; more or less plane 
anteriorly; the upper grooved, the lower perfectly smooth. A section of the teeth is wedge- 
shaped ; the base anterior. The groove in the upper incisor is either central, or central and a 
