654 RODENTS AND RABBITS xxv. 2- 



2. Classification (cont.) 



Family Zapodidae. Jumping mice. Oligocene-Recent. Holarctic 

 Zapus, jumping mouse 

 Suborder 3. Hystricomorpha 

 Nineteen families, including 



Family Hystricidae. Oligocene-Recent. Palaearctic, Africa 

 Hystrix, porcupine, Asia, Africa; Erethizon, N. American 

 porcupine, N. America 

 Family Caviidae. Pliocene-Recent. S. America 



Cavia, guinea-pig 

 Family Hydrochoeridae. Pliocene-Recent. S. America 



Hydrochoeras, capybara 

 Family Dasyproctidae. Recent. S. America 



Cuniculus, agouti (pacas) 

 Family Chinchillidae. Oligocene-Recent. S. America 



Lagostomns, vizcacha 

 Family Bathyergidae. Pleistocene-Recent. Africa 

 Bathyergus, mole-rat 

 Order 2. Lagomorpha (= Duplicidentata) 

 Family 1. *Eurymylidae. Palaeocene 



*Eurymylus, Asia 

 Family 2. Ochotonidae. Upper Oligocene-Recent 



Ochotona (= Lagomys), pika (cony), N. America 

 Family 3. Leporidae. Upper Eocene-Recent 



Lepus, hare, Pleistocene-Recent, Palaearctic, N. Africa; 

 Oryctolagus, rabbit, Pleistocene-Recent, Europe, N.Africa; 

 Sylvilagus, cotton-tail, Pleistocene-Recent, N. and S. 

 America 



3. Order Rodentia 



Rodents are mostly herbivorous and their most characteristic 

 features are, of course, in their teeth, especially the incisors, one pair 

 only of which persists in each jaw; hence they were the suborder 

 'Simplicidentata' of the older order Rodentia, which included also the 

 rabbits and hares. These latter have a second pair of upper incisors, 

 hence 'Duplicidentata'. The incisor has enamel only on its labial 

 surface and thus maintains a cutting edge. It is worn away at the rate 

 of perhaps several millimetres a week and is replaced by continual 

 growth, for which it has a very wide open pulp cavity, or in the con- 

 ventional term is said to be a 'rootless' tooth. The incisors are often 

 very large and curved and their gnawing action against each other 



