EODENTIA, CHEIROPTERA, AND INSECTIVORA. 409 



Fam. 8. Castoridce. — The best-known example of this 

 family is the Beaver {Castor fiber). The distinctive pecu- 

 liarities of the family are the presence of distinct clavicles, 

 the possession of five toes to each foot, and the fact that 

 the hind-feet are webbed, adapting the animal to a semi- 

 aquatic life. 



A considerable number of fossil Castoridce, are known, 

 commencing with the Steneofiber of the Miocene of France, 

 and the Palmocastor of the Miocene of North America. The 

 genus Castor itself is said to occur in the French Miocene, 

 and is certainly present in the Pliocene of Europe. The 

 Castor spelmus of the European cave-deposits does not appear 

 to be specifically separable from the existing Beaver {Castor 

 fiber). The great Trogontherium (fig. 684) of the Post- 

 Tertiary deposits of Europe, 

 also appears to be hardly gen- 

 erically separable from Castor. 

 The Castoroides Oliioensis of 

 the Post - Tertiary period of 

 North America seems to be 

 rightly referred to a separate 



genus. The only known ^'^- '^^-~%^Lm!o^!!r'''''' ^''''"'"' 

 species attained a compara- 

 tively gigantic size, reaching a length of about five feet. 

 Lastly, the Chalicomys of the European Miocene and Plio- 

 cene deposits appears to be nearly related to the Beavers, 

 if it be really generically distinct. 



Fa7n. 9. Muridoi. — The next family of Ptodents is that of 

 the Ifuridce, comprising the Eats, Mice, and Lemmings. In 

 this family the tail is long, always thinly haired, sometimes 

 naked and scaly. The lower incisors are narrow and pointed, 

 and there are complete clavicles. The hind-feet are fur- 

 nished with five toes, the fore-feet with four, together with 

 a rudimentary pollex. 



The remains of Mvridm are abundant in the Tertiary 

 deposits, the oldest being the extinct Myso-ps and Colonomys 

 of the Eocene of North America. In the Miocene of France 

 are various species of the extinct genus Cricetodon, allied 

 to the living Hamsters {Cricctus), together with species of 



