XV SOUTH AMERICAN RODENTS 487 
absent,’ an exceptional state of affairs in Rodents. 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-lmbs permit it to leap enormous distances. It is a 
burrowing Rodent. 
SECTION 3. HyYSTRICOMORPHA. 
Fam. 1. Octodontidae.—The Rodents of this family are of 
small to moderate size, the only, relatively speaking, giant in the 
family being the “ Water-Rat,” J/yocastor. 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, O. degus, 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 Habrocoma (more correctly, as it 
appears, to be written Abrocoma), with two species. H. bennetti 
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 ave 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. poeppigi, is a burrow- 
ing animal, from which indeed, and on account of its resemblance 
to Spalax, 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. 
2 Very probably this form should be rather, as it is by Thomas, referred to the 
neighbourhood of Pectinator, which would clear up the geographical anomaly. 
