MURIDH—ARVICOLINAX—SYNAPTOMYS. 233 
obliquity. The foramen magnum is subcireular, with somewhat of an emar- 
gination superiorly; the paroccipitals are elongated processes. In general 
shape, the skull may be called, in comparison with other skulls (except of 
Myodes), short, shallow, broad, with flattened coronal and convex frontal pro- 
file. (In ordinary Arvicola, the parietal region is highest, thence sloping 
gradually to the muzzle.) 
TABLE LVIII.— Measurements of five skulls of SYNAPTOMYS COOPERI. 
| sto ee egies | atl Scar | Se 
Dimension. = = # Ec S : =e E 23 | 
Total length (occipital protuberance to end of nasals) ..------.----- | scsoballe2ecse 1.14 | 1.07 | 1.04 | 
Greatest) zy COMmatiCniid thtemes seer aaee creas ease =l= ase sles a oee anos (ee eeee| Seeeeo 0.72 | 0.68 | 0.64 
Least width (at interorbital constriction) --.- ..---.-----..-----...- | O14: | ness 0.15 | 0.13 | 0.12 | 
VORGN TERS Unc ot CBS RE ee, See ee ee by-ctetel arse 0.25 | 0.20 | 0.17 
UGH RT CUR TONE Gane S5 Ssoas0 ee comnecno Conoco scoses Hdeoc sen arer|lsocese 0.58 | 0.55 | 0.53 
Interparoceipitalnwidth! see cesclerceen ocomeisc ieee cock ceeds see ‘ 0.37 | 0.37 | 0.37 | 
Height of skull (opposite and including last molar) 0.45 | 0.44 | 0.40 | 
Teng Lim OfsppersM OlATSOLICS = ane ccna= = aceloseee ssa aaevaaciocsmats } I 0.30 | 0.28 | 0.25 
Length of extra-alveolar portion of upper incisors...--...---.------ - 0. 24°} 0.20 | 0.20 
Henn nhtOmros trite saaeem emcees loom e esses eateae case es ac I 0.25 | 0.22 | 0.27 
From tip of under incisors to apex of coronoid ....-...--.-.....----]-----.|------ 0.62 | 0.60 | 0.57 | 
From tip of under incisors to back of condyle..---.-.---..--------- 0.70 | 0.75 | 0.79 | 0.77 | 0.70 
From tip of under incisors to end of descending process-...---..----- | 0.76 | 0.76 | 0.81 | 0.81 | 0.78 | 
ben ebhroLunder molan Genes saa serene wen ee weet e eee wasn 0.25 | 0.23 | 0.28 | 0.28 | 0.25 
Extra-alveolar portion of under incisors.---.-..---..-----.----.---- 0.22 | 0.22 | 0.25 | 0.27 | 0.25 | 
| 
As has been intimated, Synaptomys is the skull and teeth of AZyodes in 
the skin of an Arvicola, the resemblance to the latter in external features 
being strikingly complete, while the differences from A/yodes are equally 
obvious. While the ears of Myodes are minute, never reaching the level of 
the general fur, in Synaptomys the ears (now for the first time seen) are 
rather longer than they will average throughout Arvicola, in fact almost 
equaling those of Evotomys. In the Kansas skins, they come to the surface 
of the fur, though these animals are in heavy pelage; and, in the Oregon skin, 
a summer animal in poor pelage, they distinctly overtop the fur. They have 
nearly the same shape as in Evotomys; the anterior and posterior roots of 
the auricle come close together in front, but do not form a little rim as 
described under Chilotus; they are scant pilous behind, but rather more hairy 
internally on the flat portion, though the inner inflated portion is nearly naked. 
The antitragus has only very moderate development. The fore feet show 
none of the fossorial nature of those of Myodes or Cuniculus; the claws do 
