SCIURID^ 683 



the bullae are less inflated ; the rostrum is stouter ; the frontals longer, 

 and their postorbital processes set further back ; the parietals shorter ; 

 the anterior palatal foramina are nearer to the grinders, and are formed 

 equally by the maxillae and premaxillae instead of almost wholly by 

 the latter; the posterior edge of the palate is placed a little further 

 forwards ; and the maxillary zygomatic buttresses descend only about 

 halfway down the maxillae instead of to their alveolar margins (Newton, 

 op. cit. infra), 



Owen^ referred some limb bones from the Norfolk Forest Bed, 

 including a femur, tibia, astragalus, and calcaneum, to this genus, and he 

 inferred from these bones that Trogontherium was less aquatic than 

 Castor, and a swifter mover upon land. Quite recently another bone of 

 the foot — the navicular — has been discovered, and a study of this has 

 led independently to a similar conclusion.^ 



It is further of interest to note that an unworn incisor of Trogon- 

 therium presents ephemeral complications similar to those observed in 

 Castor (p. 679 above) ; these complications point back to the common 

 but very remote ancestor of all simplicidentata which must have possessed 

 brachyodont and cuspidate incisors.^ 



T. cuvieri is known in Britain only from the Norfolk Forest Bed 

 and from the High Terrace (early Pleistocene) of the Thames near 

 Greenhithe, Kent. From the former horizon numerous remains have 

 been obtained, including the magnificent skull found by Savin at East 

 Runton and described by Newton in 1891 {Trans. Zool. Soc, xiii., 165). 

 Elsewhere in Western Europe the species has been met with in the 

 Pliocene of St Prest, France, and in the early Pleistocene of Chelles, 

 France, and Mosbach and Mauer, Germany. Remains of a smaller 

 species, T. minus, have been described by Newton from the Red Crag 

 (Pliocene) of Suffolk.] 



SCIURID^. 



SQUIRRELS AND MARMOTS. 



This large family, comprising more than fifty distinct 

 genera and many hundreds of species, is distributed through- 

 out the eastern and western hemispheres with the exception 

 of their polar extremities, Madagascar, New Guinea, and 

 Australasia. As now understood, it embraces all the living 



' Owen, Geol. Mag., decade i, vi., 1869, p. 52. 



^ Hinton, Ann. Mag. Nat. Hist., January 1914, p. I9°- 



^ Hinton, op. cit., p. 189. 



