SCIURIDAE 683 
the bulle 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 maxilla and premaxillze 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 maxillze 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 Zyvogontherium 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 sz#plicidentata which must have possessed 
brachyodont and cuspidate incisors.® 
T. cuvier¢ 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 (Zrans. 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, 7. mznus, have been described by Newton from the Red Crag 
(Pliocene) of Suffolk. ] 
SCIURIDZ. 
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 1, vi., 1869, p. 52. 
1 
2 Hinton, dun. Mag. Nat. Hist, January 1914, p. Igo. 
3 Hinton, of. czz., p. 189. 
