Sus-Famity SACCOMYINAE. 
Skull delicate ; snout elongated, tapering, and acute. No ante-orbital foramen, but a wide opening directly into the 
side of the maxillary. Nasals projecting considerably in advance of the incisors. Mastoid bone very much developed, and 
forming the greater part of the upper surface of the cranium as well as the most posterior part of the occiput. Body 
slender, graceful ; hind feet elongated. Taillong. Fore claws moderate, though exceeding the hinder ones. 
The skull between the orbits is much broader than in the Geomyina. The palate is nearly 
horizontal throughout, The meatus auditorius externus is a simple pit in the swollen mastoid 
bone, without any projecting rim. Other characteristics will be found in the detailed descrip- 
tions of the genera. 
The sub-family in North America is constituted by the genera Dipodomys and Perognathus, 
both confined to the region west of the Missouri, although reaching as far north as 48° or 49°. 
Mexico has several species. The genus Saccomys' of F. Cuvier finds here its place. But little 
is ‘actually known of it, and its locality (‘‘ North America’’) is very uncertain. It. is 
supposed, however, to come from some of the West India islands. It has the upper incisors 
without any groove. The genus Heteromys® of Waterhouse also probably belongs in the same 
group, although I have been unable to find it characterized. 
1 Saccomys anthophilus, Fr. Cuv. Mem. du Museum, X, 1823, 419; plate xxvi. Supposed to have come from North 
America from having a North American plant in its pouches. 
2 A species of Héeromys (I. desmarestiana) is named, but not described, by J. E. Gray, as coming from* Coban, Centr 
America. Pr. Zool. Soc. London, XI, 1843, 79. 
