490 



MONOGRAPHS OP NORTH AMERICAN RODKNTIA. 



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Dipodomyina, witli Dipodomys alone, and Heferomyinn, including all tho rost 

 of the genera; the Heleromyinn of these authors being further subdivided 

 into those with sulcate upper incisors {Perognathus, "Abroniys", and Crice- 

 todipus) and those which have smooth upper front teeth {Ileteromys and 

 "Saccomys"). As the former author drew up his characters, excepting those 

 of the front teeth, from trivial superficialities which may be observed upon 

 inspection of stuffed skins, I am unable to gain, from his remarks, any satis- 

 factory idea respecting the degree of relationship which subsists between the 

 North American Perogna/hus and Crirctodipux on the one hand, and the Neo- 

 tropical Heteromys on the other. 



Dr. Peters's excellent characterization, which is quoted at length beyond, 

 is much more satisfactory. My im])ression is, however, that characters of 

 more than generic value will be found to distinguish these genera.* However 

 the case may stand respecting Heteromys and " Saccomys ",t it is iemon- 

 strable tiiat the genus Dipodomys is isolated from the rest by its exaggerated 

 cranial peculiarities and other less extraordinary characters. This enal)les us 

 to throw the North American genera into two subfamilies, easily character- 

 ized ; one containing Dipodomys alone, the other eml)racing Perognathus 

 and Cricetodipus. The characters are tabulated beyond. 



In these preliminary remarks respecting the valuation, definition, and 

 subdivision of the group of Pouched Mice here to be treated. I wish, for the 

 rest, to insist ujwn full generic <listiiiction between Perognathus and Criceto- 

 dipus. The latter was first satisfactorily characterized by Professor Baird as 



* Mr. Alstnii distinguishes them as genera, with tLe following chnractcrs: — 



Peroqnalhwi. — " Ears sliorler [than in .'Kpoiomys, to which other comparative exprcssioDS also refer] ; 

 tail thinl; t ircd ; soles nioro or loss nuked ; piillex with n flat nail. Skull less uiodifled ; nasals not so 

 lunch produc .; zygoma not developed into a flat plate; interparietal broad; anditor; bnlliB not pro- 

 jecting bi'hiud the occipital plane. Incisors grooved. Grinding-toeth moted, tnboronlate in yontb, 

 afterwnrd with isolated enamel-loops." 



IJderomyt. — " Liko rerogtiathm, b"t tlin fur bristly, mixed with flattened spines ; tail sbortfir, cla»l 

 with large scales and scattered hnirs. Skull with sharp supraorbital ridges; interparietol very broad. 

 Upper incisors plain. Grinding-teelh as in /'erojnaMm."— (P. Z. S. 18(t), S8.) 



t" Saccomys" is a genus which is said to have been propost^l in IMKI by Frdd. Cuvior (" Descrip- 

 tion du Saccomys anthophilo. < Mtfm. du Musi<nm d'Hist. Nat, x, lSi£1, pp. 41!M'i8") for an animal 

 supposed to bo rr.)in tho warm portion of America. Tho original acoouiit I havo not been able to consult ; 

 as described by the s..nie author in WiSt (Dent« des Mamniifisres, etc., p. 186, no. and pi. 74, ligs. a, b), the 

 animal is siiid to liuve tho " taille du l(!rot" and "abajoues ex! ^rieurus ", tho dental formula is given as 

 i. }, pni. nnd ni. },and the teeth are fully described and flgnred. but no further information upon thestrnc- 

 ture of the animal is given. Tho species is not even named formally, naturalists lieing left to infer a 

 " Sacmmi/H aitlhophiltm " from an cxprissinn used on p. 187, where " lo uom d'anthophilo " is bestowed from 

 the circumstance tliat tho pouches of the specimen examined were flilod with flowers. Mention of 

 the external cheek- pouches, however, together with the acoonnt of the teeth, renders it no less than 

 certain tl.st the genus is a member of the pnv^ont group ; and. tis alreiuly stated, there is no doubt that 

 it is a synonym of nftfwMyt. (See what llr. IVters says, as quoted ill it foregoing fiHit-note, p. 487. i 



