4 88 RODEXTIA 



about 10 inches in length, the tail somewhat exceeding 5 inches, 

 and the ears very large. Its fur is greatly valued on account of 

 its extreme softness and delicate gray colour. 



Lagidium 1 and Lagostomus. 2 — Lagidium has four digits in both 

 fore and hind feet, and Lagostomus three only in the hind feet, 

 and the auditory bulla? are much smaller than in the preceding 

 genus. Lagidium has the same distribution as Chinchilla .• while 

 Lagostomus, as represented by the Viscacha (L. trichodadylus), is 

 found in the Pampas from the Uruguay Eiver to the Rio Negro. 

 The Viscachas live in burrows, generally in large numbers, and are 

 nocturnal in their habits. Remains referable to the existing species, 

 as well as others which appear to belong to extinct forms, occur in 

 the Pleistocene deposits of South America. 



Extinct Genera. — Several Rodents from the South American 

 Tertiaries more or less closely allied to Lagostomus have been 

 described by Dr. Ameghino under the names of Prolagosfomus, 

 Pliolagostomus, etc. The huge Megamys (Potamarchus), from the 

 infra-Pampean deposits of Parana and Patagonia, is referred to this 

 family, and has dimensions approximating to those of an Ox. 

 Other fossil genera have received the names of Epiblema and Tifrn- 

 stylus. 



Family Castoroidid^e. 



Castoroicles. 3 — The large Beaver-like Rodent with the dimensions 

 of a Bear from the Pleistocene of the United States described 

 under this name is regarded by Dr. Coues as the type of a family. 

 Its dentition is nearest to that of Chinchilla and Hydmclavrus, but 

 some of the cranial characters are like those of the Castor'ulo'. The 

 genera Amblyrhiza and Loxomylus, from the Pleistocene of the 

 Antilles, appear to be allied types. 



Family Dasyproctid.-e. 



Terrestrial forms with subequal limbs, hoof-like claws, short or 

 obsolete tail, and rudimentary clavicles. Mandibular masseteric 

 ridge obsolete ; palate broad ; incisors long ; molars semi - rooted, 

 with external and internal enamel-folds. Neotropical region. 



Dasyprocta.* — Includes several slender-limbed species, with three 

 hind toes, commonly called Agoutis, inhabiting Central and South 

 America, one (D. cristata) extending into the "West-Indian Islands. 

 Numerous fossil remains of this genus occur in the cavern-deposits 

 of Brazil. 



1 Meyer, Nova Acta Ac. Cccs. Leop.-Car. vol. xvi. p. 576 (1833). 



2 Brooks, Trans. Linn. Soc. vol. xvi. p. 102(1828). 



:i Foster, Second Rep. Geol. of Ohio, p. 81 (1838). 



4 Illiger, Prodromus Syst. Mamm. p. 93 (1811). 



