DIPODOMYS. 231 



Fam. \I. Heteromyidae. 



Incisors narrow, molars rootless; mastoids enormously developed, 

 appearing on top of the skull; hind feet long, digits four or five; pel- 

 age soft. 



Sub. Fam. I. Dipodomyinae. 



Skull two-thirds as wide as long; occipital plane emarginate; 

 zygomatic plate of maxillary nearly roofing the orbit; anterior molar 

 without lobe to the prism; pit on inner side of jaws near molars. 



(>1. Dipodoiiiys. 



I. ■-■; M. ^'=l6. 



Dipodomys. Gray, Ann. & Mag. Nat. Hist. 1841, p. 521. (Type Z^. 

 philipsi. ) 

 Macrocolus, Wagn. Archiv. fur Naturg., 1846, i, p. 172. 

 Dipodops, Merr., N. Am. Faun., 1890, No. 4, p. 43. Type D. ordi. 



Skull, light, depressed, smooth, thin, broad posteriorly, tapering 

 anteriorly; anterior outline emarginate; rostrum extending beyond 

 incisors, acuminate; zygomata delicate, straight, abutting against 

 tympanies, which are greatlj" inflated and possess a nontubular orifice 

 of meatus; mastoids enormous; squamosals reduced; parietal triangle- 

 shaped, interparietal small, situated between forks of occipital; bulla; 

 in contact below the basi-sphenoid; palate terminates posteriorly 

 with a sharp median somewhat lengthened spur; external to this is a 

 fossa with two small anterior foramina, and a large one behind ptery- 

 goids with a hamular termination abutting the bullse; basioccipital 

 narrow, acuminate, reduced; separated by a fissure for its entire 

 length from the bulla; a similar fissure divides the last named bones 

 from the alisphenoid and squamosal. The interorbital foramen, or 

 what passes for one, is placed low down midwaj' on the side of the 

 rostrum; incisive foramina minute slits between incisors and molars. 

 In the rear of the skull the occipital bones appear as a rim to the 

 foramen magnum. Upper incisors sulcate, pointing backwards; 

 molars rootless. Mandible small, thick, with a conspicuous acute 

 lamina twisting obliquely outward and upward. Mental foramen 

 outside, near incisors. Hind legs elongated, tail longer than head 

 and body, penicillate; soles hairy. Hind foot with four toes only. 

 Cheek pouches large; fur of velvet softness. All the species of both 

 genera have facial crescentic lines more or less distinctly marked. 



