The Bodentia — Beaver, Marmot, etc. 



9 



The Rodents are divided into two sub-orders, namely, the 

 SimpMcidentata, which have only two upper incisor teeth; and 

 the Duplicidentata, which possess a second smaller pair, placed 

 behind the large anterior upper pair. 



Sub-order. 1. — Simplicidentata. 



This division comprises the squirrel, beaver, rat, porcu- Beaver°Ilat 

 pine, field and water voles. &c. &o. 



The " Souslik," or pouched marmot (Speanophihis) , is found Table-case 

 fossil in the Pleistocene brick-earths of the Thames Valleyjat No. 24. 

 Erith, &c. 



Squirrel, 



Fig. 8. — Profile of skull of a Rodent, Cynomyt ludovicianus (Baird), the "Prairie Marmot.'* 



The true marmot (Arctomys marmotta) is met with in the 

 Loess formation of Germany, at Champeix, in France, and many 

 other localities. 



Fig. 9.— Dentition of Beaver, Castor europceut (Owen), a the left upper, b the right 

 lower molar series. Pleistocene, Cambridgeshire Fens. 



