162 GLIRES. 
1. Thomomys talpoides. 
Cricetus talpoides, Richardson, Zool. Journ. iii. p. 518 (1828, descr. orig.) ’. 
Thomomys talpoides, Baird, Mamm. N. Am. p. 403°; Coues, Proc. Ac. Philad. 1875, p. 135°; Rep. 
Powell’s Expl. Colorado River, p. 205*; Mon. N.-Am. Rodent. p. 623’. 
Geomys umbrinus, Richardson, Faun. Bor.-Amer. i. p. 202 (1829, descr. orig.) °. 
Thomomys umbrinus, Baird, Mamm. N. Am. p. 399’; Rep. U.S. Mex. Bound. Surv. 1. Mamm. 
p- 41°. 
Thomomys talpoides umbrinus, Coues, Mon. N.-Am. Rodent. p. 628°. 
Hab. Nortu America, from the Assiniboine River southwards>.—MExico, Sonora, Santa 
Cruz (Clark, U.S. Nat. Mus.*), Espia (Kennerly, 0b.*). 
This species was found by the naturalists of the United-States Boundary Survey to 
be plentiful in the northern States of Mexico; but its exact southern range is still 
unknown. According to the observations of Messrs. Clark and Kennerly it seldom 
appears on the surface of the ground, and then only before sunrise. “ It seldom 
exposes the whole of its body in daylight. On coming to the surface, if the grass is 
sufficiently near to be reached, it seizes a sprig and drags it within the entrance [of its 
burrow], and with its fore feet packs it away in its pouches; when this operation is 
complete the opening [of the burrow] is filled up with loose earth, which has been 
aptly described by suggesting its resemblance to the emptied contents of a flower-pot.” 
When surprised at any distance from its hole the animal becomes bewildered, and is 
then easily captured ®. 
3. DIPODOMYS. 
Dipodomys, Gray, Ann. & Mag. Nat. Hist. vii. p. 521 (1840). 
Macrocolus, Wagner, Arch. f. Naturg. xii. 1, p. 172 (1846). 
As already indicated, the members of the subfamily Heteromyine differ greatly in 
appearance from the Geomyine, being slender Jerboa-like Rodents, with elongated 
hind limbs and tail. Their skulls are comparatively delicate, with slender zygomatic 
arches; and usually with enormously developed mastoids, which often occupy a consi- 
derable part of the top of the cranium as well as of its occipital surface. Of the three 
well-marked genera now known, the present is characterized by its densely haired tail 
and soles, plain ungrooved incisors, rootless molars, and remarkable skull, in which the 
inflation of the temporal regions is carried to an extreme. 
Two species of the genus Dipodomys have usually been recognized, agreeing in their 
peculiar tawny mouse-colour, with white-striped heads, haunches, and tails, but 
differing in size and proportions. There is no doubt that the Dipodomys of the Rocky- 
Mountain subregion, D. ordi, is usually a larger and stouter animal, with a propor- 
tionally shorter tail and lighter coloration than the D. phillipsi of the Pacific slopes. 
But Dr. Coues finds such a perfect series of gradations, that he treats the former 
