102 MAMMALIA ORDER V.RODENTIA. 



while another species has spines mingled with the fur. The Brazilian genus 

 Holochilus, which includes the largest American rats, differs by the relatively 

 larger last upper molar and the stouter skull. Another allied type are the fish- 

 eating rats (Ichtkyomys) of South America, characterised by the webbed and 

 fringed hind-feet, and their aquatic and probably fish-eating habits, while 

 Nectomys is another allied Peruvian form. The rice-rat (Siymodon hispidus), 

 ranging from the United States to Ecuador, -differs markedly iromSitomys in 

 the pattern of the tubercles on the molar teeth. Writing of these rats, 

 Mr. G. Lincecum, in the American Naturalist for 1872, states that they 

 dwell together on the prairies of Texas in families in much the same manner 

 as the prairie-marmot. '* They prefer light sandy soil on the prairie, where 

 the shivered limy sandstone crops out ; but where the prairie is enclosed and 

 cultivated they take possession of the fencing, and burrowing under the 

 bottom rail, excavate sufficient cells, and construct their copious grassy beds 

 there. Out on the prairie, in the wild state, they make one principal burrow, 

 in front of which they pile up the earth that comes from all their subter- 

 ranean galleries. They rarely extend their main burrow more than eight or 

 nine inches in depth, while their underground passages are seldom more 

 than four or five inches below the surface. They also construct several 

 secret outlets, opening 10 or 12 inches from the main hole, which opening 

 they very ingeniously conceal by strewing a few grass blades over it ; and so, 

 when the rat-hunter attacks the citadel, the inmates escape through some of 

 the concealed passages. Eight or nine inches deep, and turned a little to one 

 side in the main hole, is a cavity, seven or eight inches in diameter, filled 

 with fine, soft grass blades, which must be quite warm and pleasant, serving 

 the family for winter-quarters. During the hot months they construct nice 

 grass beds in a basin-like cavity, which they dig out under the sides of tufts 

 of grass, or heaps of bush." From all the above the South American genus 

 Rhithrodon, with five rat-like species, and the North American Rhithrodont- 

 omysj containing three species of the size of large mice, differ in their 

 grooved upper incisors. Another well-marked type of the group is pre- 

 sented by the North American wood-rats (Neotoma), in which the molars 

 simulate the prismatic pattern characteristic of the voles. Certain species in 

 which the tail is very bushy have been separated generically as Teonoma ; 

 while N. alleni has been referred to a distinct genus under the name of 

 Hodomys. The next five genera of cricetines are confined to the island of 

 Madagascar, where they are the sole representatives of the Rodent order. Of 

 these, Hypogeomys is a large fawn-coloured rat, with large ears and feet and 

 a long tail ; Nesomys includes two long-haired rufous species ; Brachytarsomys 

 contains a single rat with velvety fawn-coloured fur, short feet, and a long tail ; 

 the single species of Hallomys differs from Nesomys by the much longer hind 

 feet ; while the two dormouse-like representatives of Miurus are easily recog- 

 nised by the short and nearly naked ears, and by the long tail being bushy, 

 except on its basal third, where it is scaly. The last representative of the sub- 

 family is the crested rat (Lophiomys imhausi) of North-Eastern Africa, so 

 named on account of the crest of long hair running along the back. This very 

 large rat, which is arboreal in its habits, differs from all other members of the 

 family in the first toe of the fore-foot being opposable, the rudimental collar- 

 bones, and by the bony roof covering the muscles of the hinder part of the 

 skull. All the hair is long, the long tail bushy, and the colour black and 

 white. The animal has quite unnecessarily been made the type of a distinct 

 family. 



