MUUID^— AUVICOLIN/K— SYNAl'TOMYS. 



233 



ol)liquity. The foramen mngnum is subcircular, with somcwlmt of an emiir- 

 gination superiorly; the paroccipitals are elongated jjroccsses. In general 

 shape, the skull may be called, in comparison with other skulls (except of 

 Mijodes), 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.) 



Tadlk LVIII. — Meaturcmenta of five skulls of Svhaitomys coopkiii. 



Dimension. 



Total length (occipital protuberenco to end of nosalii) .. 



Greatest zygoniiitio width 



Least width (at interorbital constriction) 



Width of rostrnin 



Intertnastoid width 



Interparoccipital width 



Height of skull (opposite and including last molar) 



Length of upper molar series 



Length of extra-alveolar portion of upper incisors 



Length of rostrum 



From tip of under incisors to apex of coronoid 



From tip of under incisors to back of condyle 



From tip of under incisors to end of descending process. 



Length of under molar series , 



Extra-alveolar portion of under incisors 



0.14 



0.36 

 0.26 

 0.17 

 0.87 



0.70 

 0.7C 

 0.85 

 0.28 



S '5' 

 *2. 



0.27 



0.75 

 0.76 

 0.23 

 0.22 



f- as 



to * 



f5M 



to -J. 



if 



1.14 



0.72 

 0.15 

 0.85 

 0.58 

 0.37 

 0.45 

 0.30 

 0.84 

 0.85 

 0.08 

 0.79 

 0.81 

 0.28 

 0.85 



1.07 

 0.G8 

 0.13 

 0.80 

 0.55 



o.:i7 



0.44 

 0.88 

 0.80 

 0.88 

 0.60 

 0.77 

 0.81 

 0.28 

 0.87 



c a 



1.04 

 0.04 

 0.18 

 0.17 

 0.53 

 0.37 

 0.40 

 0.85 

 0.80 

 0.87 

 0.57 

 0.70 

 0.78 

 0.85 

 0.85 



As has been intimated, Synaptomys is the skull and teeth of Mi/odes 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 Myodex are minute, never reaching the level of 

 the general fur, in Synaptomys tlie ears (now for the first time seen) are 

 rather lunger than they will average throughout Arvicola, in fact almost 

 ceualing those of Evotomyn. In the Kansas skitis, they come to the surface 

 ot the fur, though these animals arc 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 Evototnys; the anterior and posterior roots of 

 the auricle come close together in front, but do not form a little rim as 

 described under Chilottis; they are scant pilous behind, but rather more iiairy 

 internally on the flat portion, though the inner inflated portion is nearly naked. 

 The antitragus has only very moderate development. The fore feet show 

 uouo of the fossorial nature of those of Myodes or Ci/miculus ; the claws do 



