CHAP. XVII.] MAMMALIA. 235 



Sciurus (100 — 120 sp., including the sub-genera Spermosciurus, 

 Xerus, Macroxus, Eheithrosciurus, and Ehinosciurus), comprises 

 the true squirrels, and occupies the area of the whole family 

 wherever woods and forests occur. The approximate number of 

 species in each region is as follows : Nearctic 18, Paleearctic 6, 

 Ethiopian 18, Oriental 50, Australian (Celebes) 5, Neotropical 30. 

 Sciuropterus (16 — 19 sp.), comprises the flat-tailed flying squirrels, 

 which range from Lapland and Finland to North China and Japan, 

 and southward through India and Ceylon, to Malacca and Java, 

 with a species in Formosa ; while in North America they occur 

 from Labrador to British Columbia, and south to Minnesota and 

 Southern California. Pteromys (12 sp.), comprising the round- 

 tailed flying squirrels, is a more southern form, being confined to 

 the wooded regions of India from the Western Himalayas to Java 

 and Borneo, with species in Formosa and Japan. Tamias{b sp.), 

 the ground squirrels, are chiefly North American, ranging from 

 Mexico to Puget's Sound on the west coast, and from Virginia to 

 Montreal on the Atlantic coast; while one species is found over all 

 northern Asia. Spermo'philus (26 sp.), the pouched marmots, are 

 confined to the Nearctic and Palsearctic regions ; in the former ex- 

 tending from the Arctic Ocean to Mexico and the west coast, but 

 not passing east of Lake Michigan and the lower Mississippi; in the 

 latter from Silesia through South Eussia to the Amoor and Kams- 

 chatka, most abundant in the desert plains of Tartary and Mon- 

 golia. Ardomys (8 sp.), the marmots, are found in the northern 

 parts of North America as far down as Virginia and Nebraska 

 to the Eocky Mountains and British Columbia, but not in Cali- 

 fornia ; and from the Swiss Alps eastward to Lake Baikal and 

 Kamschatka, and south as far as the Himalayas, above 8,000 feet 

 elevation. Cynomys (2 sp.), the prairie-dogs, inhabit the plains 

 east of the Eocky Mountains from the Upper Missouri to the 

 Eed Eiver and Eio Grande (Plate XIX., vol. ii. p. 129). Anoma- 

 lurus (5 sp.), consists of animals which resemble flying-squirrels, 

 but differ from all other members of the family in some points of 

 internal structure. They form a very aberrant portion of the 

 Sciuridse, and, according to some naturalists, a distinct family. 

 They inhabit West Africa and the island of Fernando Po. 



