SACC0MYIDJ5— DIPODOMYIN^}— DIPODOMYS. 5C5 



sponding measurement of the hind limb, that is, from the knee outward, is 

 three-fifths or more of the whole length, and the hind foot alone is about one- 

 third of such dimension. There is no noticeable bulkiness of the haunches, 

 but the hams are massive, flattened-conoidal, suddenly contracting at the 

 lower third, where the cms is of much less calibre than the foot. There is 

 a prominent heel, and an obvious tendo Achillis. The metatarsus is subcylin- 

 drical, widening to a broad foot with strong digits. The whole foot reminds 

 one of a rabbit's ; a resemblance heightened by the dense furring of the whole 

 sole, excepting a small calcaneal tuberosity. There are four perfect digits, 

 of which the 3d is the longest, the 4th and 2d are successively a little shorter, 

 and the 5th is much shorter still; while the 1st is a mere rudiment, entirely 

 removed from the rest, nearly halfway up the foot. This bears a stumpy 

 claw; the other claws, though small, are well formed, stout at base, com- 

 pressed, little curved, and acute. 



The tail exceeds the head and body in length, even without the penicil- 

 late tuft of hairs at the end, which projects an inch or more beyond the ver- 

 tebras. It is of somewhat quadrangular shape, the flattening being especially 

 appreciable on the under side, and is of nearly uniform calibre throughout, 

 springing directly from the body without any basal enlargement, and but little 

 taper at the end. It is closely and uniformly clothed with rather stiffish hairs 

 for most of its length, the hairs gradually lengthening on the further half into 

 the well-formed terminal brush. 



The pelage differs from that of the allied genus Perognatkus in its soft- 

 ness, length, and fineness, and has a silky gloss in life. It also lies with 

 extreme smoothness on the colored areas of the body; the hairs are plumbe- 

 ous basally, as usual ; on the white parts they are unicolor to the roots. 



In the male, during the rutting season, there is an immense perinseal 

 enlargement, strictly circumscribed from neighboring parts, due to the turgid- 

 ity of the virile organs within. The anus presents in the centre of this 

 enlargement with the sheath of the penis just in front, quite prominent. 

 There is a comparatively large os penis. In the female, the anal and genital 

 orifices are in still closer relation ; the ostium vaginas is prolonged in front 

 into a dependent lobe, occupying the site of the penial sheath of the male. 



The pattern of coloration of Dipodomys is peculiar and diagnostic of the 

 genus — the striped tail and white band across the hips are not found else- 

 where. All the upper parts are fulvous or tawny-brown, closely lined with 



