1915.] 



INTRODUCTION. 



15 



by Dr. Merriam to be the case with the very similar and closely 

 related genus Geomys. ^ The vibrissse are of just sufficient length 

 to span the diameter of the burrow and doubtless serve as a further 

 substitute for eyes. 



The general pelage is fine and silky, becoming long, full, and soft in 

 winter in cold climates and agam becoming thin and harsh in summer. 

 In the southern tropical or subtropical species the fur, if it may be 

 caUed fur, seems not to attain the full soft winter coat. The pelage 

 consists of a fine all-plumbeous underfur tlirough which rises a 

 longer, coarser coat with plumbeous base and colored tips which give 

 the domuiant shade characterizing the species. This usually varies 

 considerably with the season, in some species becoming much darker 

 in winter, in others much paler. The covering on the underparts is 

 usually much thinner, often allowing the skin to show through. The 

 tail, ears, and tops of feet are but thinly clothed with short, stiff hairs. 

 The small nose-pad is naked. 



The construction of the mouth is such that both upper and lower in- 

 cisors protrude from fur-incased mandibles, allowing perfect freedom 

 for cutting roots, digging in hard earth, or prying out stones without 

 danger of the earth entering the real mouth, which opens vertically 

 well back of the incisors and closes automatically as the incisors are 

 spread wide apart. The fur-bordered lips close m a vertical slit in 

 front of the real mouth or draw back and expose an ample cavity and 

 a thick, fleshy tongue. 



The pockets, which give the animal unusual mterest, have been the 

 cause of much speculation and misapprehension. Some of the speci- 

 mens first seen by naturalists were stuffed with the pockets wrong side 

 out, Say's genus Pseudostoma bemg based on such a specimen, while 

 Kuhl's SaccopJiorus was based on a specimen showing the pockets in 

 their real position. The use of the pockets is still often misunderstood. 

 They are external invaginated folds of skin, fm- Imed, and openmg 

 along each cheek parallel with the mouth and extendmg approximately 

 li to 2 inches back under the skui of the shoulder. They are very 

 elastic and when empty might pass unnoticed, but when filled they 

 more than double the apparent size of the animal's head. I have often 

 thrust two fingers half their length into the two pockets of a small-sized 

 gopher, reaching back almost to the middle of the animal's body. In 

 large species the thumb fits nicely in the empty pocket. In removing 

 a gopher's skin a thin band of muscle is discovered attached to the apex 

 of each pocket and by it they are drawn back and kept in place. The 

 pockets can not be fuUy everted without greatly stretchmg or possibly 

 breaking this muscular attachment, but they can be drawn out so that 

 a large fold of the lining will hang out of the pocket when the animal's 

 muscles are relaxed. It is a common belief that the pockets are used 



IN. Am. Fauna No. s, 16, 1895. 



