490 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
. 
Dipodomyina, with Dipodomys alone, and Heteromyina, including all the rest 
of the genera; the Heteromyina 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 (deteromys 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, [am unable to gain, from his remarks, any satis- 
factory idea respecting the degree of relationship which subsists between the 
North American Perognathus and Cricctodipus 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”,t 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 Dipodomys, 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; interparictal broad ; auditory bulla not pro- 
jecting behind the occipital plane. Incisors grooved. Grinding-tceth rooted, tuberculate in youth, 
afterward with isolated enamel-loops.” 
Heteromys.—‘ 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. Grinding-teeth as in Perognathus.”—(P, Z. S. 1876, 88.) 
t“Saccomys” is a genus which is said to have been proposed in 1823 by Fréd. Cuvier (“ Deserip- 
tion du Saccomys anthophile. < Mém. du Muséum d’Hist. Nat. x, 1823, pp. 419-428”) for an animal 
supposed to be from the warm portion of America. The original account I haye not been able to consult ; 
as described by the same author in 1825 (Dents des Mammiféres, ete., p. 186, no. and pl. 74, figs. a, b), the 
animal is said to have the “ taille du lérot” and “abajoues extérieures”, the dental formula is given as 
1. 3, pm. and m. 4,and the teeth are fully described and 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 
“ Saccomys anthophilus” from an expression used on p- 187, where “le nom d’anthopbile” is bestowed from 
the circumstance that the pouches of the specimen examined were filled with flowers. Mention of 
the external cheek-pouches, however, together with the account of the teeth, renders it no less than 
certain-tlat the genus is a member of the present group; and, as already stated, there is no doubt that 
it is a synonym of Heteromys. (See what lr. Peters says, as quoted in a foregoing foot-note, p. 487.) 
