470 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
only a notch and not a foramen results, the correspondence of the whole 
opening with the pyriform slit of the Muride@ is very evident, and the relation 
of the parts is fully established, though the shape is quite different. 
The contour of the parts surrounding the foramen is such that the zygo- 
matic process of the maxillary stands out at a right angle at a point scarcely 
above the level of the alveoli. The anterior root of the zygoma is hence 
notably depressed in position; there being no forward-upward reach of the 
lower border of this arch, so evident in Muride. The zygoma, in fact, is 
nearly horizontal in all of its length along the under side; but anteriorly the 
upper edge rises prominently, in consequence of the unusual extension of the 
malar up the maxillary, already mentioned. The malar runs all the way up 
to the lachrymal bone, affording a circumstance which I believe to be rare, 
namely, a lachrymo-malar suture like that which is found in Dipodide and 
Pedetide. This ascending spur of the malar is, moreover, expanded into a 
rather broad lamina, partly defending the orbit, thus supplying a wall that, in 
most cases, is afforded by expansion of the zygomatic process of the maxil- 
lary; the latter being in this case of styloid character. In its continuity, 
the malar is a slender rod; behind, it underlaps a short spur of the squamosal 
with simple squamous suture. d 
The general shape of the orbit is much the same as in Mus. In both, 
the squamosal forms much of the posterior orbital wall; the orbito-sphenoid 
being correspondingly reduced. The antero-exterior corner of the parietal 
reaches to the brim of the orbit. 
The rostral portion of the skull bears to the rest about the same propor- 
tion as in Mus, and is equally attenuate anteriorly, though thicker at the base, 
and consequently more tapering. The ends of the nasals project conspicu- 
ously beyond the plane of the incisors; behind, these bones terminate oppo- 
site the ends of the intermaxillaries; the suture of the frontal with each of 
them, as well as with the maxillaries, being nearly in one transverse jagged 
line. The intermaxillaries develope a strong alveolar plate, separating the 
superior incisors for nearly half their length; this, with the projection of the 
nasals and backward set of the much-curved teeth, results in a snout strikingly 
like that of the Saccomyide. The feeble, retreating under jaw, densely hairy 
upper lip, and small nasal pads bear out this resemblance in the external 
physiognomy. 
As in Mus, the interorbital constriction is moderate, being about as wide 
