ill 



1 1 1 ■' 



I 



m 

 m 



500 



MONOGJiAPUH OF NOKTU AMEItlUAN liUUENTIA. 



todipuH break npnrt across Ihe nii(l<llo. Tli'm seetns to be chiefly due to the 

 delicate state of tlie zygomata, wliich alFonl no stable connection between 

 tiie fore and aft parts. Tiie breait occurs at the l)asis|»lioiio-occipitaI, sijuaino- 

 niasloid, and t'ronto-parictal sutures; the parielals, temporals excepting Mjunm- 

 osals, witjj the occiptal, coming away from the rest of the skull. 



There appears to be something peculiar, in the habits |)crhap8, rather 

 tiian in the scarcity, of Ihe species, which prevents the acquisition of largo 

 series of specimens in this family. While hundreds of examples of animals 

 no larger or more conspicuous than these are readily omassed, collections are 

 all deficient in Perognothus and Cricetodipun, and not very fiill in Dipodomys. 

 I have not been al)le to examine more than a hundred specimens altogether, 

 and of these more than half were Dipodomi/.t. Of Perognathus, I have, how- 

 ever, specimens of all the described North American species, including all 

 of Baird's types and considerable additional material. After protracted exam- 

 ination, I endorse the validity of all the species admitted by that author in 

 18.57, and find indications of the probable existence of one or two more. This 

 point is fully discussed beyond. The species that appear to be established 

 may be readily determined by the following analysis: — 



Analgiii of Ihe Specie$ of I'kiioonatiius. 



A. Notch of the ear bonnded iu front by n aliglit, though distinct, lobe of the tragns. Whole fore Ifg 



white. 

 a. Toil peuicillute, crested nt the end, rather longer than the body and head. Sides with uo fulvona 



stripe ; PENICILLATUS. 



ft. Tail simple ; sides with a strong fulvons stripe. 



1. Tail decidedly shorter than the body and hea<1. Length aboat 4 inches. Pelage niuderitely 



stiff. Mixed saudy and blackish fasciatl's. 



2. Tail not sliorter than head and body. Length about 3 inches. Pelage very hispid. Mixed 



cinnamon and blackish : iiisPiDf j. 



B. Notch of car formed in front directly by the edge of the conch. Fore leg mostly colored like the back. 



Tail simple; lateral stripe obscure monticoiji, 



■ PEROGNATHUS FASCIATUS, Maxim. 



PerosniMiut fmeiatut, Maxim., N. Act. Akad. Leop.-Cies. Nat. Cnr. xiz, pt. i, 1839, 369, pi. 34 ; Reise Nord- 

 Am. i, ISSg, 449 ; Arch. f. Natnrg. 1861, p. — ; Verz. Heiso, 186i, 175, pi 4, f. 6, 7.— Wagn., 

 Arcb. f. Naturg. 1841, 45 ; Snppl. Schreb. iii, 1843, 613.— Schinz, 8yn Mamm. ii, 1845, 859.— 

 LeC, Proo. Acad. Nat. 8ci. Pbiia. vi, 1853, 824.— Aud. &. Bacr., Q. N. A. iii, 1854, 341 (com- 



1 piled.— OiEBEL, Siingeth. 1855, 572 (compiled).— Bd., M. N. A. 1857, 421 (Chihnahna).— Bd., 



U. 8. Hex. Bound. Snrv. ii, pt. ii, 1859, Mamm. 42.— Scckl., P. R. R. Rep. xii, pt. ii, 1860, 101 

 (compiled).— Gray, P. / 3. 1868, SOI.— Coues, Proo. Phila. Acad. 1875, 284 (monographic). 



Perognatut fasceatiit, LmCECtJM, Am. Nnt. vi, 1872, p. 369 (habits). 



Prognathut faoeatut, Linoecum, Am. Sportsman, Feb. 23, 1874 (habits). 



Diagnosis. — Largest of the genus ; considerably exceeding Hexperomys 

 leucopus, and approaching Tomias quadrivittatus, iii bise ; length four inches 



'f&fi 



