MURIDAIX—SIGMODONTES—NEOTOMA. 9 
appearances are obscure or lost. Upper molars mostly 3-rooted; under with 
only two roots apiece. 
In amplification of the characters of this genus, we continue: 
Neotoma shows us the largest murine skull of North America, and many 
strong generic characters. The zygomatic width is relatively greater than in 
other forms, amounting to half the length of the skull, mainly in consequence 
of the outward obliquity of the zygomata, which diverge from each other as 
they pass backward, instead of lying nearly parallel. The same length 
of skull, with parallel zygomata, would much exceed twice the zygomatic 
width. They also do not dip so low down as in most other genera, not descend- 
ing to the level of the palate; and the union of the jugals with the squamosal 
spurs is abrupt, almost angular. In general contour, there is an observable 
difference in the two sections of the genus—that with scant-haired tail and 
the bushy-tailed species; the latter having the rostral portion of the skull 
more lengthened and the interorbital constriction greater. In NW. floridana 
the interorbital width is about one-seventh of the total length, and rather 
exceeds the rostral diameter, though this is swollen. The nasals are much 
widened anteriorly, where they end with crescentic outline; behind, they 
stop opposite the anterior roots of the zygomata, and always (we believe) in 
advance of the nasal branches of the intermaxillaries, which reach into the 
interorbital constriction. In most other genera, there is no special difference 
between the length of the nasals and the intermaxillary behind, or else the 
difference is fluctuating. At the extreme antero-superior corner of the 
orbit, the maxillary, just where it unites with the frontal, throws up a tubercle 
for muscular attachment stronger than we have noticed in other genera. The 
thin plate of the superior maxillary that forms the outer wall of the anteor- 
bital foramen has a gently-rounded anterior border, with its convexity looking 
forward, instead of running into a sharp point as in S¢gmodon, where the 
same edge is deeply concave by reason of this pointed process; and likewise, 
when looked down upon from above, the foramen-appears as merely an emar- 
gination instead of a nearly-closed oval. The edge of the orbit is sharp 
above, but not beaded. The interparietal is moderate and subquadrate, with 
a spur; the paroccipital processes are strong;. the tympanic bullse medium ; 
the pterygoids large, hamulate, and fenestrate. The foramen magnum is 
remarkable for its depressed elliptical shape, being usually much wider than 
high; the condyles are far apart at the ends of the major axis. The palate 
ends behind as a simple shelf with concave border opposite the last molars 
