F. 



amily HYSTRICID^E. 



By several recent systematic writers, the New World Porcupines have 

 been widely separated from their Old World relatives ; these authors placing 

 them in different families. The two forms that differ most widely in cranial 

 characters are Erethizon and Hystrix, especially in respect to the degree of 

 inflation of the skull ; but the other forms, in a measure, bridge over the wide 

 gap existing between these two types in respect to this feature. The Ameri- 

 can Porcupines form a group collectively separable as a subfamily, by quite 

 tangible characters, from the Porcupines of the Old World. While the 

 former are arboreal, the latter are terrestrial, and the two types present modi- 

 fications of structure adapting them to these widely different modes of life. 

 There is, however, running through the whole, a strong degree of resemblance. 

 The Synetherina* or the American Porcupines, differ from the Old World 

 Porcupines in the form of the skull; in having the clavicles perfect; in the 

 tail being generally (not, however, in Erethizon) more or less prehensile; in 

 the molar teeth being fully rooted, and placed in more or less converging 

 series; in not having five toes to all the feet (generally only four both before 

 and behind) ; in the soles being tuberculated instead of smooth ; in the upper 

 lip being undivided by a vertical groove ; in the form of the lachrymal bone ; 

 and in various other more or less important osteological characters. 



The subfamily Synetherince is most numerously represented in South 

 America, where occur three of its four genera, namely, Chcetomys. Synefheres, 

 and Sphin gurus ;f the fourth, Erethizon, being its only representative in 

 North America north of Mexico. While these genera have many features 

 in common, and constitute a very natural and well circumscribed group, 

 Erethizon differs from the others in having five instead of four toes on the 



* Synetherina Gervais, Zool. et Paleont. franc., 1848-52, p. 18 ; SpMngurince Alston, Proc. Zool. Soc. 

 Lond., 187G, 93; = CercolaVinw of the family Spalacopodida: of Lilljeborg (Systematisk CEfversigt af de 

 Gnagaude Diiggdjuren, Glires, 1866, p. 51) and of Gill (Arrang. Families of Mammals, p. 22). 



\Synetherc8 and Sphingurus F. Cuvier, 1822, = Cercolabes Brandt, 1855. 



25 M S85 



