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MOXOGKAPUS OF NORTH AMERICAN UODENTIA. 



hiiul feet, and in liaving a short, spiny, non-prehensile tail. The South Ameri- 

 can genus ClicEtoinijs dillers from all of the others in the conformation of the 

 skull ; the malar hone is developed to a remarkable degree, more than in 

 any other Rodent, excepting Calogenyn, the postorbital process of which 

 nearly joins that of tlie frontal, so as to almost wholly separate the orbital 

 and temporal fossae. The portion of the palate between the molar teeth is 

 also longer and narrower, and the temporal ridges arc more highly developed, 

 wiiilc the molars themselves present important difiercnccs. The tail is 

 lengthened and rat-like, scantily clothed with hair, and scaly, though to some 

 degree prehensile. The genera Synethercs and Spkiiigurus differ somewhat 

 from Erethizon in their cranial and dental characters, and have the tail strongly 

 prehensile, while the feet (as also iti C/icctoiiii/.s) arc all four-toed. Syncthercs 

 dilfers i'wm Sj>hingi/rus in the broad, highly arched form of the frontal region 

 of the skull, and in the greater development of the spines. Chcetomys has 

 l)ut a single species (f. subupinosus), which is confined to the nortliern and 

 central portions of Brazil. Spliingurus and Syiwtheres have each several com- 

 monly recognized species, which are distributed throughout the greater part 

 of South and Central America, from Paraguay to Southeastern Mexico and 

 the West Indies ; none, however, occur west of the Andes. All the species 

 arc of rather small size in comparison with tho representatives of Erethizon; 

 the body rarely exceeding eighteen inches in length. 



Considerable variation in the form of the frontal region of the skull 

 occurs among both the Hystricin(S and the Synethcrince. In this respect, 

 Synetheres approaches Hystrix, while the Old AVorld genus Atherura, with 

 its tlattened skull, more resembles Erethizon. Even diiferent species of 

 Hystrix vary considerably in respect to the inflation and convexity of tiiis 

 portion of the cranium, showing that this is a feature of no very great taxo- 

 nomic importance, though giving rise to striking differences in respect to the 

 dorsal contour of the skull. ; 



Genus ERETHIZON E. Cuv. 



North American Forcoplnes. 



JSi/jfrir, in part, of earlier writers. 



ICrelhison F. CuviBH, M6m. du Mus., ix, 1822, 426, 433. - -, 



EMnoprocia Gray, Proc. Zoul. Soo. Lond., 1665, 321. 



Toes four in front and five behind, all armed with strong, curved claws. 

 Tail short, thick, depressed, non-prehensile, covered above at the base with 



