632 RODENTIA. 



to existing families and genera, and they seem to have under- 

 gone but little change since that period. There is no sugges- 

 tion as to their origin, but similarities have been pointed out 

 between them and the Proboscidea and Typotheria, the 

 latter resembling them in their jaws, teeth, nasal bones and 

 paroccipital processes of the skull. 



Sub-order 1. SIMPLICIDENTATA. 



With one pair of upper incisors, without vesiculae seminales. 

 testes abdominal, descending into a temporary scrotum. 

 The fibula does not articulate with the calcaneum. 



Tribe 1. Sciuromorpha. 



Skull with slender zygomatic arch, clavicles well developed, fibula free, 

 infraorbital foramen small except in Anomaluridae. 



Fam. 1. Anomaluridae. Arboreal forms, with their limbs connected 

 by a patagium, supported by a cartilaginous fascia arising from the ole- 

 cranon ; tail long, hairy, with large scales on its ventral surface near the 

 root ; p \ ; molars with transverse enamel loops ; Ethiopian. Anoma- 

 lurus Wat., 9 sp. Idiurus Matsch., 1 sp. Zenkeretla Matsch., 1 sp. 



Fam. 2. Seiuridae. Squirrels. Arboreal or terrestrial, with cylin- 

 drical hairy tails, often brilliantly coloured ; skull with postorbital pro- 

 cesses, p y> molars rooted, tubercular ; cosmopolitan, excluding Austral- 

 asian region and Madagascar. Bheithrosciurus Gray, 1 sp., Borneo, with 

 grooved incisors. Xerus H. and E., spiny squirrels, Afr. (Ethiopian and 

 Palaearctic), 5 sp., terrestrial, burrowers. Sciurus L., cosmopol., except 

 Austr. and Madgr., 106 sp. ; manus 4 digits and reduced pollex, pes 5 

 digits, first upper p. minute, soon lost ; no cheek pouches ; >SV vulgaris, 

 common English squirrel, ranges to Japan. Tamias 111., ground squirrels, 

 chipmunk, Nearctic, 30 sp., Palaearctic, 1 sp., with cheek pouches. Sper- 

 mophilus F. Cuv., pouched marmots, sousliks, burrowers, Nearct., Palae- 

 arct., 40 sp. Cynomys Raf., prairie dogs, burrowers, live in com- 

 munities, often with a burrowing owl and a rattlesnake, Nearct., 4 sp. 

 Arctomys Schr., marmots, burrowers, Nearct., Palaearct., 10 sp. ; A. 

 marmotta, the alpine marmot. Eupetaurus Thos., flying squirrel, Ori- 

 ental, 1 sp., patagium as in the next, with hypsodont grinders. Petau- 

 rista Link. (Pteromys G. Cuv.), flying squirrels, Oriental, 13 sp., limbs 

 united by an expansion, the support of which articulates with the carpus. 

 Sciuropterus F. Cuv., flying squirrels, Oriental 17 sp., Nearct. 5 sp., 

 Palaearct. 2 sp., patagium as in the last. Nannosciurus Trouess., Ethiop. 

 1 sp., Oriental 2 sp. Extinct genera from the U. Eocene onwards. 



Fam. 3. Castoridae. Beavers, p \, molars rootless, without post- 

 orbital process, stomach with a large glandular appendage, anus and 

 urinogenital duct open into a common cloaca, pes webbed. Castor L., 

 burrowers on the banks of rivers, 2 sp. ; C. fiber, European, formerly 

 British, do not as a rule make dams ; C. canadensis, N. Amer., construct 

 dams. Extinct sp. and genera from the Miocene onwards. 



Fam. 4. Haplodontidae. Haplodon (Aplodontia) Rich., 2 sp., Nearct. 



