MURID^—AEViCOLlNjE— SYNAPTOMYS. 



233 



obliquity. The foramen magnum is subcircular, 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 fire skulls of Synaptomys cooperi. 



Dimension. 



Total length (oeeipital protuberance to end of nasals) .. 



Greatest zygomatic width 



Least width (at interorbital constriction) 



Width of rostrum 



Intermastoid width 



Interparoecipital width 



Height of skull (opposite and including last molar) 



Length of upper molar series 



Length of extra-alveolar portion of upper iucisors 



Length of rostrum 



From tip of under iucisors to apex of coronoid 



From tip of under incisors to back of condyle 



From tip of under iucisors to end of descending process- 

 Length of under molar series 



Extra-alveolar portion of under iucisors 



0.14 



0.36 

 0.26 

 0.17 

 0.27 



0.70 

 0.76 

 0.25 

 0.22 



zq 



0.27 



0.75 

 0.76 

 0.23 



0.22 



a a 



1.14 

 0.72 

 0.15 

 0.25 

 0.58 

 0.37 

 0.45 

 0.30 

 0.24 

 0.25 

 0.62 

 0.79 

 0.81 

 0.28 

 0.25 



o 



si* 



1.07 

 0.68 

 0.13 

 0.20 

 0.55 

 0.37 

 0.44 

 0.28 

 0.20 

 0.22 

 O.GO 

 0.77 

 0.81 

 0.28 

 0.27 



ds a 



c a 



1.04 

 0.64 

 0.12 

 0.17 

 0.53 

 0.37 

 0.40 

 0.25 

 0.20 

 0.27 

 0.57 

 0.70 

 0.78 

 0.25 

 0.25 



As has been intimated, Synaptomys is the skull and teeth of Myodes in 

 the skin of an Arvicola, the resemblance to the latter in external features 

 being strikingly complete, while the differences from Myodes 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 



