452 RODENTIA 



temporary assumption during the breeding season of a distinctly 

 ornamental coat, corresponding to the breeding-plumage of birds. 

 For the greater part of the year the animal is of a uniform gray 

 colour ; but about December its back becomes a brilliant orange- 

 yellow, which lasts until about March, when it is again replaced by 

 gray. The Squirrel shown in Fig. 200 is a native of Burma and 

 Tenasserim, and is closely allied to 8. caniceps, but goes through no 

 seasonal change of colour. 



" The number of species in the genus is about 75, of which 3 

 belong to the Palsearctic, 15 to the Ethiopian, about 40 to the 

 Oriental, and 1 6 to the combined Nearctic and Neotropical regions " 

 (Thomas). 



Fossil species referred to Sciimis are found in the European 

 Tertiaries down to the Phosphorites of Central France, while others 

 occur in the White River Miocene of the United States. 



Rhithrostiurus} — A very striking Squirrel, confined to Borneo, 

 and as yet only known from three or four examples, has been 

 separated generically under this name. The general shape of its 

 skull is very different from that of other Squirrels ; but its most 

 peculiar characteristic is the presence of from seven to ten minute 

 parallel vertical grooves running down the front face of its incisors ; 

 no other Squirrel having really grooved incisors, and no other 

 member of the Avhole order incisive grooves resembling these. 

 Its premolars number i and its molars are simpler and less ridged 

 than in the other genera. This Squirrel (E. /microtis) is far larger 

 than the English, Math an enormously long bushy tail, long tufted 

 ears, and black and white bands down its sides. 



Xerns. 2 - — Fur coarse and spiny. Claws long and comparatively 

 straight. Ear-conchs minute or absent. Skull with the postorbital 

 processes short and directed backwards, the bony palate prolonged 

 considerably behind the tooth-row, and the external ridge on the 

 front face of the anterior zygomatic root more developed, and 

 continued much farther upwards than in Sciimis. Premolars f ; 

 molars as in Sciurus. Mammae two. This genus contains four well- 

 marked species, known as Spiny Squirrels, all natives of Africa. 

 They are terrestrial in their habits, living in burrows which they 

 dig for themselves. X. getulus, a striped species of North Africa, 

 has much the size and appearance of the Indian Palm-Squirrel : 

 all the others are a little lai'ger than the English Squirrel. 



Tamias. 3 — All the members of this genus are characterised by 

 the possession of internal cheek-pouches, and by their style of colora- 

 tion ; being ornamented on the back with alternate light and dark 

 bands. Their skulls are slenderer and lighter than those of the 



1 Gray, Ann. Mag. Nat. Hist. ser. 3, vol. xx. p. 272 (1867). 



2 Hemprich and Ehrenberg, Synth,,/, Phys. Mamm. vol. i. (1832). 



3 Illiger, Prodromus Syst. Mamm. p. 83 (1811). 



