146 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
The foregoing table is made up of measurements published by Baird in 
1857, with those of twelve additional specimens. The dry measurements are, 
of course, only approximately correct, and, as far as the total length of body 
is concerned, are a little over the truth, from over-stuffing, as is certainly the 
case with No. 1092. Probably no one of them was in life over 4.00 at the 
outside, and the real average cannot be over 3.50, instead of 3.60, as the fig- 
ures stand. No. 2872, which we have not seen, is most likely ungrown. 
These circumstances tend to bring the maxima and minima a little nearer 
together, say 4.00 and 2.75 for total length, &e. 
On comparing this table with that of A. rudi/us, it will be seen that the 
average size is greater; that the tail-vertebraee average about a third of an 
inch longer, and the tail with its hairs little if any longer, showing the great 
difference in the length of the terminal pencil; the foot is 0.72 instead of 
about 0.70 on an average. The tables also show that while gappert touches 
figures that swéidus rarely reaches, and that the average of the latter is near 
the minimum of the former, especially as regards tail, feet, and ears, that 
nevertheless the intergradation is complete. 
Description of the skull and teeth of A. Gappert.—Aside from the generic 
features given under head of Evotomys, the skull of gapperi does not differ very 
noticeably from that of Arvicola in general. It averages in length 0.95, by 0.52 
in zygomatic breadth, or about as 100 to 55. The interorbital constriction is 
about as broad as the rostral portion of the skull. The molar series is one-fifth 
or barely more of the total length. The upper incisors protrude a little less, and 
the under a little more, than the length of the molar series. In the lower jaw, 
the distance from the tip of the incisors to the end of the hamular process 
equals or is even less than the distance from the same point to the back of the 
condyle. This is as in Pitymys, and not as in the riparius section of Arvicola, 
where the former measurement exceeds the latter. The height of the skull, 
measured from the last molar inclusive perpendicularly upward, is just about 
one-third of the length. The interparietal bone is acute-angled laterally; 
there is a little foveole on the frontal; the nasal branch of the premaxillary 
is not longer than the nasal bone, and neither extends back of the anterior 
root of the zygoma. The tympanic bull are very much inflated and papery ; 
the foramen magnum is large and subcireular. The incisive palatal foramina 
are long and narrow; the anteorbital are as usual in the subfamily. In adult 
skulls, the muscular impressions are distinct, leaving a shield-shaped plateau 
on top of the skull. 
