490 MONOGRAPHS OF NORTH AMERICAN BODENTIA. 



Dipodomyina, with Dipodomys alone, and llchro/iniina, i Deluding all the real 

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

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

 todipus} and those which have smooth upper front teeth {Heteromys and 

 "Sarrnun s"). As the former author drew up Ins characters, excepting (hose 

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

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

 factory idea respecting the degree of relationship which subsists between the 

 North American Perognathus and Cricetodipus 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 impression 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", f it is demon- 

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

 cranial peculiarities and other less extraordinary characters. This enables us 

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

 ized; one containing Dipodomys alone, the other embracing 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 upon full generic distinction between Perognathus and Criceto- 

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



' Mr. Alston distinguishes them as genera, with the following characters: — 



Perognathus. — " Ears shorter [than in llipodomijs, to which other comparative expressions also refer] ; 

 tail thinly haired ; soles more or less naked ; pollex with a flat nail. Skull less modified ; nasals not so 

 much produced ; zygoma not developed into a flat plate; interparietal broad; auditory bulls not pro- 

 jecting behind the occipital plane. Incisors grooved. Griudiug-teeth rooted, tuberculate in youth, 

 afterward with isolated enamel-loops.'' 



Heierorays. — " Like Perognathus, but the fur bristly, mixed with flattened spines ; tail shorter, clad 

 with large scales and scattered hairs. Skull with sharp supraorbital ridges; interparietal very broad. 

 Upper incisors plain. Grindiug-tceth as in Perognathus.''— (P. Z. S. 187(1, 88.) 



i •■ Saccomys " is a genus which is said to have been proposed in 1823 by Fred. Cuvier (" Descrip- 

 tion iiu Saccomys anthophilo. < Mem. du Museum d'liist. Nat. x, 1823, pp. 419-428") for au animal 

 supposed to be IV mi the warm portion of America. Theoriginal account I have not beeu able to consult ; 

 a> described by the same author in 1825 (Dents des Maiumiferes, etc., p. 18(1, no. and pi. 74, ligs. a, li), the 

 animal is said to have the " taille du lerot " and •• abajoues exterieures", the dental formula is given as 

 i. . pm. and m. [.and the teeth are fnl ly described ami figured, but no further information upon the struc- 

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

 Sa< i omgs anthophilua " from an expression used on p, 187, where " le nom d'anthophile " is bestowed from 

 the circumstance thai the pouches of the specimen examined were filled with flowers. Mention of 

 tlie external eheek-ponclies, however, together with the account of the teeth, renders it no less than 

 certain thai the genus is a member of the present group : and, ns already stated, there is no doubt that 

 it is .i s\ noiivm ol //■ t< romy I see what llr. Peters says, as quoted in a lorcgoiug foot-note, p. 187. 



