XV SOUTH AMERICAN RODENTS 487 



absent/ an excieptional state of affairs in Eodents. A singular 

 fact in the anatomy of this animal is the existence of a septum 

 dividing the lower part of the trachea. This is sometimes met 

 with in birds. As might be supposed from its large eyes, the 

 Spring Haas, as the animal is sometimes called, is nocturnal. Its 

 long hind-limbs permit it to leap enormous distances. It is a 

 burrowing; Eodent. 



Section 3. Hystpjcomorpha. 



Fam, 1. Octodontidae. — The Eodents of this family are of 

 small to moderate size, the only, relatively speaking, giant in the 

 family being the " Water- Eat," Myocastor. The toes are with 

 but one exception not reduced ; the tail is long in the majority 

 of the genera. The teats are placed high up on the sides of the 

 body. The clavicle is fully ossified. All the genera are South 

 or Central American in range with the exception of Petromys} 



Sub-Fam. 1. Octodontinae. — Octodon has four species, which 

 are all Chilian, Peruvian, and Bolivian in distribution. The 

 Degu, 0. deyus, has a length of 160 mm., with a tail 105 mm. 

 long. The ears are 18 mm. long. At the roots of the claws 

 are longish and stiff hairs which appear to serve as " combs." 

 The tail has long but sparsely scattered hairs. There are twelve 

 pairs of ribs. The lengths of the various sections of the intestine 

 are as follows: small intestine, 680 mm.; caecum, 90 mm.; large 

 intestine, 390 mm. These animals live in large companies. 

 Closely allied is the genus Hahrocoma (more correctly, as it 

 appears, to be written Ahrocoma), with two species. H. hennetti 

 is 204 mm. long, with a tail of 103 mm. The ears are long, 

 22 mm. The fore-feet have no outward trace of the thumb. 

 Stiff hairs like those that characterise Octodon are found also in 

 this genus. The fur is very soft. The furring of the tail is 

 much thicker than in Octodon. 



Spalacopus with but a single species, S. jjoeppigi, is a burrow- 

 ing animal, from which indeed, and on account of its resemblance 

 to S-palax, it has received its name. The ears in accordance with 

 the underground life are short, only 5 mm. in length in an 



1 Parsons, Proc. Zool. Soc. 1898, p. 858. 



^ Very probably this form should be ratlier, as it is by Thomas, referred to the 

 neighbourhood oi Pectinator, which would clear up the geographical anomaly. 



