484 RODENTIA 
Carterodon1—This genus, which was originally described upon 
the evidence of skulls from the Brazil caves, but subsequently found 
living, is readily distinguished by the broad and grooved incisors. 
The upper molars have one inner and two outer enamel-folds ; 
those of the lower jaw being the reverse of this. 
Fossil Forms.—Remains of the existing genus Loncheres occur in 
the Brazilian cave-deposits, which also yield the extinct Dicolpomys. 
A large number of fossil Octodontide from the Tertiaries of South 
America have been described under many generic names, but it 
will be sufficient to mention that Phloramys and Pithanotomys are 
considered to be allied to Ctenomys ; while Jlvrenia, Orthomys, and 
Trilodon show affinity to Myopotamus. Pellegrinia, from the Pleisto- 
cene of Sicily, may be allied both to Ctenodactylus and Octodon. 
Family THERIDOMYIDA. 
This extinct family, which is represented in the Tertiaries of 
Europe and the United States, comprises several genera of com- 
paratively small Rodents, which are regarded by Dr. Schlosser as 
nearly related to the Octodontide, although connected by Archwomys 
with the Chinchillide. The dental formula is the same as in the 
Octodontide. In the typical genus Theridomys, from the Lower 
Miocene and Upper Eocene of Europe, the molars are rooted, and 
have three or four re-entering enamel-folds, which form isolated 
discs on the worn crowns. Syllophodus, from the Miocene of the 
United States, is closely allied. Protechinomys and Trechomys are 
genera from the Phosphorites of Central France with rooted molars ; 
while in dArchwomys of the same deposits the molars are rootless, 
with the enamel-folds dividing their crowns into lamine, as in the 
Chinchillas. 
Family HystrRicip 2. 
Build stout. Limbs subequal. A number of long and stout 
spines in the integument. Facial portion of skull short and broad, 
and the jugal without an inferior angle. Molars with external and 
internal enamel-folds ; completely or partly rooted. 
Subfamily Synetherinze.—Molars rooted ; clavicles complete ; 
upper lip not cleft; soles tuberculated; pollex absent; four mamme ; 
tail generally prehensile; spines mixed with long hairs. This group 
is confined to America, all the forms except one being arboreal, 
and their habits less strictly nocturnal than in the next subfamily. 
There are three genera. 
Erethizon.2—Represented by the common Canadian Porcupine 
1 Waterhouse, Nat, Hist. of Mami. vol. ii, p- 351 (1848). 
> F. Cuvier, Dents des Mammiferes, p. 256 (1825) 
