NATURAL SCIENCES OP PHILADELPHIA. 301 



the Middle Faunal Province, from the British Possessions (lat. 

 49, Coues) to Chihuahua, Mexico. (In the Pacific region re- 

 placed b3 r C. parvus.) 



Description (from numerous alcoholic and dry specimens, in- 

 cluding Baird's types). In general points of exterior conformation 

 this animal is so similar to species of Perognathus already fully 

 treated, that the account of these features may be abridged. The 

 generic character of structure of the ear and hairiness of the 

 sole, with the diminutive size, are the chief points. The ear is 

 very small and simple, not overtopping the fur of the parts. It 

 is evenly rounded ; there is no lobation whatever of either anti- 

 tragus or tragus, the slight notch which exists being formed in 

 front by the folded-over edge of the ear itself, and behind by the 

 antitragal ridge. The head is full, especially in the frontal region, 

 tapering to a bluntly conical snout, which is densely hairy except- 

 ing a minute nasal pad ; the upper lip is heavily pilous with a 

 fringe of hairs which droop over and hide the incisors. The eye 

 is rather small, and nearer to the ear than to the nose. The 

 whiskers are very numerous and fine, the longest exceeding the 

 head. On the palms are observed posteriorly two great tubercles, 

 of which the inner is much the largest ; there are others at the 

 base of the 2d and 5th, and of the conjoined 3d and 4th digits 

 respectively; otherwise the palm is studded with minute granu- 

 lations. The thumb is rudimentary, bearing a small flat nail ; 

 the other claws are of ordinary character ; 3d longest ; 4th little 

 less ; 2d shorter ; 5th still shorter. The hairiness of the soles 

 posteriorly is a generic character in comparison with Perognathus; 

 anteriorly granular, with a small tubercle at the base of each digit, 

 and another on the outer side of the metatarsus a little way up. 

 The small size of the hind feet, however, is one of the most obvious 

 distinctions from G. Parvus. The longest hind foot measured 

 in upward of twenty cases is only 0.70 long, or barely one-third 

 of the length of head and body, while the average is much below 

 this, and the minimum is only about one-fourth of the length of 

 the head and body. We may say simply that the foot is usually 

 nearer one-fourth than one-third of this dimension. Similarly the 

 shortness of the tail is a second character. In a large series, the 

 vertebrae of the tail average just exactly as long as the head and 

 body ; in no case does the tail exceed the body and head by more 

 than 0.25 of an inch, and this length is only exceptionally reached. 



