n8 



RODENTS. 



in a popular -work like the present to point out its distinctive peculiarities without 

 the aid of a series of figures. It may be mentioned, however, that the frontal 

 region between the eye-sockets is much narrowed; and that in the zygomatic, or 



cheek-arch, the cheek 

 (jugal) bone is usually 

 reduced to a mere 

 splint occupying the 

 middle of the arch. 

 Again, the lower sur- 

 face of the process 

 arising from the upper 

 jawbone to form the 

 front half of the 

 cheek-arch is more or 

 less flattened out into 

 a nearly perpendicular 

 plate: while the vacuity in the front of the eye for the passage of the nerves of 

 the face is generally of considerable height, and wider above than below. 



The number of genera and species belonging to this family is so great that it 

 is impossible to notice more than a small moiety in this work. Accordingly, only 

 representatives of the various subfamilies into which these Rodents are divided, 

 and such forms as are of general interest, are selected for description. 



SKELETON AND MOLARS OF BROWN RAT. 



The Australian" Rats. 

 Genus Hydromys. 



The Australian rats, of which there is one aquatic species, together with an 

 allied terrestrial fori., from the same region, constitute a subfamily distinguished 

 from all the other mice by having only two pairs of molar teeth in each jaw : these 

 teeth being rooted, and having their crowns divided into distinct lobes. 



The Australian water-rat (Hydromys chrysogaster) is a rat-like aquatic Rodent, 

 with broad and partially-webbed feet, the webs and claws being larger in the 

 hinder than in the front-limbs. The fur of the back is black with an admixture 

 of golden-coloured hairs ; the under-parts being of a dark golden hue, save for a 

 narrow stripe of flaxen running from the lower part of the neck to the middle of 

 the belly. Except for its terminal fifth, which is flaxen-coloured, the tail is black. 

 The tip of the muzzle is thickly covered with hairs, by means of which the nostrils 

 can be closed. The length of the head and body is about 2 feet, and that of the 

 tail half as much. The skull differs in the form of the front portion of the cheek- 

 arch from the ordinary murine type. This species is confined to Australia and 

 Tasmania, where it is known to the colonists as the beaver-rat. It is thoroughly 

 aquatic in its habits, and is not uncommon on the banks of the rivers : while it is 

 at times seen on the seashore. It is an inhabitant of Australia, Tasmania, and 

 New Guinea, 



The Queensland rat (Xerom/ys myoides) is a terrestrial species of about double 



