The genus Lophiomys,[312] represented only by L. imhausi (Fig. 204) of North-East Africa, differs from the typical Muridæ in having the temporal fossæ roofed over by a thin plate of bone, rudimentary clavicles, and an opposable hallux. On these grounds it has been made the type of a family, but since all the features are Murine—the dentition being that of a typical Cricetine—it appears doubtful whether that distinction is justifiable. The hair forms a crest along on the back, and is of a peculiar structure. The habits of this Rodent are arboreal.

Family Muridæ.

Skull (Fig. 203) with contracted frontals; a short and slender jugal, generally reduced to a splint between the zygomatic processes of the maxilla and squamosal; the lower root of the former process more or less flattened into a perpendicular plate; typically, the infraorbital vacuity tall, and wide above and narrow below. Lower incisors compressed; no premolars;[313] molars rooted, or rootless, tuberculate, or with angular enamel-folds. Pollex rudimental; tail generally nearly naked and scaly. Habits various, but mostly terrestrial.

This large and cosmopolitan family, which includes more than a third of the existing Rodents, is represented by about forty genera.

Subfamily Hydromyinæ.—Molars ²⁄₂ in number, rooted, and divided into transverse lobes. Represented by two Australasian genera.

Hydromys.[314]—External form modified for an aquatic life. Tip of muzzle extensively haired, so that the nostrils can be closed. Skull with the infraorbital vacuity crescentic, scarcely narrowed below, and its external wall without the perpendicular zygomatic plate characteristic of most of the family; incisive foramina very small.

Two species, with habits like those of the Water Voles, are known from Australia, Tasmania, and New Guinea. In the typical H. chrysogaster the colour of the back is black, with an admixture of golden-coloured hairs; the belly being of a dark golden hue.[315]

Xeromys.[316]—External form Murine. Tip of muzzle as in Mus, not as in Hydromys. Toes unwebbed. Tail scaly, very finely haired. Skull as in Mus, with the exception of the rounding of the supraorbital edges. Teeth as in Hydromys.

Represented by X. myoides, of Queensland; a species about twice the size of the Common Mouse. This genus serves to connect Hydromys with the other Murines, although it is difficult to say to which group it comes nearest.

Subfamily Platacanthomyinæ.—Molars rooted, with transverse laminæ. Flattened spines mingled with the hair; tail thickly haired. Represented by one genus.

Platacanthomys.[317]—The one representative of this genus is P. lasiurus, found in the clefts of rocks and hollow trees in Southern India at elevations of about 3000 feet. This elegant little animal closely resembles a Dormouse; the tail and body having a length of 6 inches.

Subfamily Gerbillinæ.—Incisors narrow; molars with transverse laminæ (Fig. 205). Auditory bullæ very large in most cases. Hind limbs elongated. Tail usually long and hairy. Ranges over the Palæarctic, Oriental, and Ethiopian regions.

Gerbillus.[318]—Upper incisors grooved; first molar with three laminæ, second with two, and third with one. There are some sixty species, with a range coextensive with that of the family. The Gerbils, with their large and bright eyes and long tufted tails, are very graceful creatures, inhabiting sandy plains, where they form extensive burrows. Remains of existing species are found in cavern-deposits in Madras (Fig. 205).

Pachyuromys.[319]—The African genus Pachyuromys is distinguished by the very large size of the auditory bulla, as well as by the short and fleshy tail, which is club-shaped. The incisors are narrow and faintly grooved.

Mystromys,[320] Otomys,[321] and Dasymys.[322]—These genera, also from South Africa, differ from Gerbillus in the form of the molars, and are represented by a few species.

Malacomys.[323]—The one known species of this genus is from the Gaboon, and is in some respect intermediate between the true Gerbils and the Rats. Thus the dentition and feet are those of the former, but the long scaly tail resembles that of the latter.

Subfamily Phlœomyinæ.[324]—This subfamily is represented only by Phlœomys[325] cumingi, of the Philippine Islands, in which the incisors are very broad, the molars are divided into transverse laminæ, and the claws are large. The muzzle is blunt; the ears are hairy externally; the tail is moderate, and thickly haired; and the auditory bullæ are very small. The first upper molar has three, and the others two laminæ.

Subfamily Dendromyinæ.—Incisors convex in front; molars ³⁄₃, rooted and tuberculated. Ears hairy; claws long. Confined to the Ethiopian region.

Dendromys.[326]—A small Rodent, with the habits of a Dormouse, characterised by its grooved incisors, slender form, and long, scaly tail, which is sparsely haired. Two other Murines described as Steatomys[327] and Lophuromys[328] are referred to this subfamily. The first is of plump form, with a rather short and thickly haired tail, and grooved incisors. The latter resembles Steatomys in form, but has fine flattened bristles instead of fur, and plain incisors.

Subfamily Cricetinæ.—Molars ²⁄₃, tuberculate and rooted, with the tubercles of the upper ones arranged in two longitudinal rows (Fig. 206, B). This subfamily has an almost cosmopolitan distribution, and appears to include the most generalised members of the family, from which the more specialised Murinæ have been evolved.

Cricetus.[329]—According to the arrangement proposed by Mr. O. Thomas[330] this genus is taken to include both the Hamsters of the Old World (Cricetus proper) and the white-footed or Vesper Mice (Hesperomys) of the New. Cheek-pouches are frequently present, and may be very large. The first molar (Fig. 206, B) generally has six tubercles. The tail may be very short.

This large and unwieldy genus may be divided into a number of groups or subgenera. The typical group includes the Hamsters of the Old World, characterised by the large size of their cheek-pouches, the walls of which are connected with muscles arising from the lumbar vertebræ. The tail is remarkable for its shortness. The best-known species is C. frumentarius, inhabiting Europe and Northern Asia. The American forms, which range over the whole of that continent, comprise a number of subgenera, of which the following are the most important. Rhipidomys, including Dormouse-like forms with long tails and a dentition like that of the typical group; Oryzomys, represented by Murine species; Calomys, with short tail and Hamster-like body; Vesperimus, with only five tubercles on the first molar; Onychomys, in which the tail is extremely short and Hamster-like, and the form is Arvicoline; Scapteromys, of Murine form with a long and hairy tail; Phyllotis, with a shorter tail; Habrothrix, an Arvicoline group, with a short and thinly haired tail; and Oxymycterus, distinguished from the preceding by having a nail instead of a claw on the pollex. With regard to the distribution of these forms Mr. Thomas[331] remarks that in South America as we proceed southwards there is a general tendency “to a disappearance of the tropical and northern Mouse- and Dormouse-like subgenera Rhipidomys, Vesperimus, and Oryzomys, with the appearance and increase of the Vole- and Hamster-like Habrothrix and Calomys—a change that is curiously paralleled in the Old World by the gradual supercession of Mus and Myoxus in favour of Arvicola and Cricetus as we go northwards from tropical to temperate and arctic regions.” One species has spines in the fur.

Remains of Cricetus are abundant in the Pleistocene cavern-deposits of Brazil, where a number of the forms are referable to existing species; the genus is also represented in the Miocene of North America and Europe, the species from the former area having been described as Eomys, and those from the latter as Cricetodon.

Holochilus[332] (Nectomys).—The Rats of this genus are allied to the American forms of Cricetus, but have the third upper molars proportionately larger and the skull more stoutly built. This genus is confined to Brazil, and contains about six species, some of which are the largest indigenous Rats of America. Two species are aquatic in their habits, and have short webs between the toes of their hind feet.

Sigmodon[333] differs from Cricetus in the pattern of the molar teeth. It contains one species only, the Rice-Rat, S. hispidus, ranging from the United States to Ecuador.

Rhithrodon,[334] and Ochetodon.[335]—These are more or less like Cricetus, but with grooved upper incisors. The first, is a South-American genus, and contains five Rat-like species, one from Venezuela, another from Peru, and the other three from Patagonia. The second consists of three North American mice, of about the size and proportions of the English Wood-Mouse (Mus sylvaticus).

Neotoma.[336]—A peculiar North American genus, in which the teeth simulate the prismatic appearance of those of the Arvicolinæ. There are four species known as Wood-Rats, all of about the size of Mus decumanus; one of them (N. cinerea) having a tail almost as bushy as a Squirrel’s while the other three have ordinary scaly Rat-like tails.

Fossil remains of Neotoma from cavern-deposits in Pennsylvania are not improbably referable to the existing Florida Rat (N. floridana). Paciculus, from the Miocene of the United States, is regarded as an allied extinct genus with enamel-folds to the molars.

Hypogeomys.[337]—This and the following genera are confined to Madagascar, where they are the sole representatives of the Rodentia. Hypogeomys is a very peculiar form of large size, with long ears, feet, and tail. There is only one species, H. antimena, a fawn-coloured Rat about 9 inches long.

Nesomys.[338]—Contains two species of long-haired Rats, more or less rufous in colour, about the size of the Brown Rat.

Brachytarsomys.[339]—Represented only by B. albicauda, a pretty velvety-haired fawn-coloured Rat, with short feet and a long tail.

Hallomys.[340]—The only species (H. audeberti) is very like a Nesomys, but has much longer hind feet.

Eliurus.[341]—Represented by one small Dormouse-like species, characterised by its nearly naked and short ears, and long tail, of which the proximal third is scaly, and the remainder covered with long hair. The pollex is rudimental, but the hallux well developed.

Subfamily Arvicolinæ.—Molars usually imperfectly rooted or rootless, and composed of two longitudinal rows of triangular prisms placed alternately (Fig. 207). Tail moderate or short. Common to the Palæarctic and Nearctic regions.

The Voles, as the members of this group are commonly termed, are so closely connected with the Cricetines that they may be regarded merely as a branch of that subfamily which has attained a peculiarly specialised type of molar dentition. The Voles are externally distinguished, as a rule, from true Rats and Mice by their more clumsy and heavy build and less graceful movements; by the small size of their eyes, the bluntness of the muzzle, the small ears, and the shorter limbs and tail.

Phenacomys.[342]—A North American genus distinguished by its rooted molars, and thus connecting the typical forms with Cricetines like Neotoma. Several species have been described by Dr. C. H. Merriam.

Arvicola.[343]—The type genus Arvicola has rootless molars, and naked soles to the feet. It includes over forty species inhabiting Europe, North America, and Asia, a few species entering into the northern limits of the Oriental region in India. Three species of the genus are found in the British Isles, of which the following account is given by Mr. O. Thomas:—

The common Water-Vole (A. amphibius) is as large as the Brown Rat. Its fur is long, soft, and thick, of a uniform grizzled brown all over, except when, as is not uncommon, it is wholly black. The tail is about half the length of its head and body, and the hind feet are unusually long and powerful, although not webbed, and have five rounded pads on their lower surfaces. Its molar teeth (see Fig. 207) present the following number of prismatic spaces:—in the upper jaw the first, or anterior, has 5, the second 4, and the third 4, of which the last is very irregular in shape, and is sometimes itself divided into two, making 5 in all; in the lower jaw the first has 7 spaces, of which the 3 anterior are generally not fully separated from one another, the second has 5, and the third 3. These numbers for the different teeth are taken as the characters of the subgenus Paludicola of Dr. Blasius, by whom this method of subdividing the genus was first introduced. The Water-Vole is one of the commonest English mammals, and is perhaps the most often actually seen of all, owing to its diurnal habits. It frequents rivers and streams, burrowing deeply into their banks, and in this way often causing considerable damage. Its food consists almost wholly of water-weeds, rushes, and other vegetable substances, but, like so many other Rodents, it will also occasionally eat animal food, in the shape of insects, mice, or young birds. The female during the warm season of the year has three or four litters, each of from two to seven young. The range of the Water-Vole extends over the whole of Europe and North Asia, from England to China, but it is not found in Ireland. The common Field-Vole, or short-tailed Field-Mouse (A. agrestis), representing the subgenus Agricola, is about the size of a House-Mouse, but with a short stumpy body, and a tail only about one third the length of the head and body combined. Its hind feet have six pads on their inferior surfaces. The colour is dull grizzled brown above, and grayish-white below. Its molar teeth have respectively 5, 5, and 6 prismatic spaces above, and 9, 5, and 3 below. The Field-Vole is one of the commonest of our smaller mammals, and frequents fields, woods, and gardens in enormous numbers, often doing very considerable damage in the latter, owing to its fondness for garden produce of all kinds. It is spread over the whole of Great Britain from the Hebrides southwards. Abroad its range extends from Finland to North Italy and from France and Spain to Russia. The Bank-Vole (A. glareolus) resembles in size and general appearance the common Field-Vole, but may be distinguished by its more or less rusty or rufous-coloured back, its larger ears, and the relatively longer tail, which attains to about half the length of the head and body. Its molar teeth present characters so different from those of all other Voles as to have caused it to be regarded as belonging to an entirely distinct genus, for which the name of Evotomys has been used. Their chief distinction lies in the fact that, unlike those of all other Voles, their pulp-cavities close up in adult life, and they form distinct roots, more resembling those of the ordinary Rats and Mice. The enamel-spaces of these teeth number respectively 5, 4, and 5 above, and 7, 3, and 3 below. The habits of this species are in every way similar to those of the Field-Vole. Its range in Great Britain extends northwards to Morayshire, beyond which it has not yet been observed. It is also found all along the north temperate zone from France to China, and is replaced in North America by a closely allied animal known as A. gapperi. It is probable, however, that both A. gapperi and A. glareolus are only southern climatic offshoots of a still more northern species, the A. rutilus of Northern Europe, Siberia, and Arctic America.

Fossil remains of Arvicola are common in European Pleistocene deposits, and they have also been obtained from the Upper Pliocene of the Norwich Crag.

Synaptomys.[344]—Represented by one North American species, having grooved upper incisors, skull and molars like those of Myodes, with the external characters of Arvicola.

Myodes.[345]—Distinguished from Arvicola by the more clumsy build, convex obtuse head, extremely short and Rabbit-like tail, short ears, small feet, the soles of which are furred, elongated claws, and thick fur, as well as by the breadth and massiveness of the skull, in which the zygomatic arch has a laminar expansion and the palate a peculiar contour; while the root of the lower incisor does not extend behind the last molar, the upper incisors are bevelled, and not grooved, and the molars have a characteristic pattern, which cannot be well explained without a figure.

The Lemmings, as the members of the genus are commonly called, are represented by the Norwegian Lemming (M. lemmus, Fig. 208), and the North American M. obensis. Different individuals of the Norwegian Lemming vary considerably both in size and colour, but its usual length is about 5 inches, and its soft fur yellowish brown, marked with spots of dark brown and black. It has a short, rounded head, obtuse muzzle, small bead-like eyes, and short rounded ears, nearly concealed by the fur. The tail is very short. The feet are small, each with five claws, those of the fore feet strongest, and fitted for scratching and digging. The usual dwelling place of the Lemmings is in the highlands or fells of the great central mountain chain of Norway and Sweden, from the southern branches of the Langfjeldene in Christiansand-stift to the North Cape and the Varangerfjord. South of the Arctic circle they are, under ordinary circumstances, exclusively confined to the plateaus covered with dwarf birch and juniper above the conifer region, though in Tromsö-amt and in Finmarken they occur in all suitable localities down to the level of the sea. The nest is formed under a tussock of grass or a stone, constructed of short dry straws, and usually lined with hair. The number of young in each nest is generally five, sometimes only three, but occasionally seven or eight, and at least two broods are produced annually. Their food is entirely vegetable, especially grass-roots and stalks, shoots of the dwarf birch, reindeer-lichens, and mosses, in search of which they form, in winter, long galleries through the turf or under the snow. They are restless, courageous, and pugnacious little animals. When suddenly disturbed, instead of trying to escape they will sit upright, with their back against a stone or other coign of vantage, hissing and showing fight in a very determined manner (Fig. 208).

The circumstance which has given more popular interest to the Lemming than to a host of other species of the same order of animals is that certain districts of the cultivated lands of Norway and Sweden, where in ordinary circumstances they are quite unknown, are occasionally and at very uncertain intervals, varying from five to twenty or more years, literally overrun by an army of these little creatures, which steadily and slowly advance, always in the same direction, and regardless of all obstacles, swimming across streams and even lakes of several miles in breadth, and committing considerable devastation on their line of march by the quantity of food they consume. In their turn they are pursued and harassed by crowds of beasts and birds of prey, as bears, wolves, foxes, dogs, wild cats, stoats, weasels, eagles, hawks, and owls, and never spared by man; even the domestic animals not usually predaceous, as cattle, goats, and reindeer, are said to join in the destruction, stamping them to the ground with their feet, and even eating their bodies. Numbers also die from diseases apparently produced from overcrowding. None ever return by the course by which they came, and the onward march of the survivors never ceases until they reach the sea, into which they plunge, and swimming onwards in the same direction as before perish in the waves. These extraordinary and sudden appearances of vast bodies of Lemmings, and their singular habit of persistently pursuing the same onward course of migration, have given rise to various speculations, from the ancient belief of the Norwegian peasants, shared in by Olaus Magnus, that they fall down from the clouds, to the almost equally untenable hypothesis, ingeniously maintained by the late Mr. W. D. Crotch, that they are acting in these migrations in obedience to an instinct inherited from vastly ancient times, and are still seeking the congenial home in a supposed submerged Atlantis, to which their ancestors of the Miocene period were wont to resort when driven from their ordinary dwelling-places by crowding or scarcity of food. The principal really ascertained facts regarding these migrations seem to be as follows. When any combination of circumstances has occasioned an increase in the numbers of the Lemmings in their ordinary dwelling-places, impelled by the restless or migratory instinct possessed in a less developed degree by so many of their congeners, a movement takes place at the edge of the elevated plateau, and a migration towards the lower-lying land begins. The whole body moves forward slowly, always advancing in the same general direction in which they originally started, but following more or less the course of the great valleys. They only travel by night; and, staying in congenial places for considerable periods, with unaccustomed abundance of provender, notwithstanding all the destructive influences to which they are exposed, they multiply excessively during their journey, having families still more numerous and more frequently than in their usual homes. The progress may last from one to three years, according to the route taken, and the distance to be traversed until the sea-coast is reached, which in a country so surrounded by water as the Scandinavian peninsula must be the ultimate goal of such a journey. This may be either the Atlantic or the Gulf of Bothnia, according as the migration has commenced from the west or the east side of the central elevated plateau. Those that finally perish in the sea, committing what appears to be a voluntary suicide, are only acting under the same blind impulse which has led them previously to cross smaller pieces of water with safety.

Cuniculus.[346]—Cranial and incisive characters those of Myodes, in the main, but the molars more of an Arvicoline type, the first upper one differing from that of all other members of the family in having seven prisms. Externally of the general shape of Myodes, but distinguished by the absence of external ears, the shortness and dense furring of the feet, the obsolete pollex with rudimentary nail, and the great length of the two middle claws of the manus. Represented by one species, the Banded Lemming (C. torquatus), of the Arctic region.

Remains of both C. torquatus and Myodes lemmus occur in British Pleistocene deposits.

Fiber.[347]—Closely allied to Arvicola, both externally and in cranial and dental characters, but with the tail nearly as long as the body (apart from the head), compressed, nearly naked, and reticulate. Feet incompletely webbed, and the whole body adapted for a thoroughly aquatic life.

The Musk-Rat or Musquash (F. zibethicus, Fig. 209) is the only representative of this genus, and the largest member of the subfamily, the head and body being about 12 inches in length. It is rather a heavily built animal, with a broad head, no distinct neck, and short limbs; the eyes are small, and the ears project very little beyond the fur. The fore limbs have four toes and a rudimentary thumb, all with claws; the hind limbs are larger, with five distinct toes, united by short webs at their bases. The tail is laterally compressed, nearly naked, and scaly. The hair much resembles that of a beaver, but is shorter; it consists of a thick soft under-fur interspersed with longer stiff, glistening hairs, which overlie and conceal the former on the upper surface and sides of the body. The general colour is dark umber-brown, almost black on the back and gray below. The tail and naked parts of the feet are black. The musky odour from which it derives its name is due to the secretion of a large gland situated in the inguinal region, and present in both sexes.

The Musk-Rat is peculiar to America, being extensively distributed in suitable localities in the northern part of the continent, extending from the Atlantic to the Pacific, and from the Rio Grande to the barren grounds bordering the Arctic Seas. It is aquatic in its habits, living on the shores of lakes and rivers, swimming and diving with great facility, feeding on the roots, stems, and leaves of water-plants, or on fruits and vegetables which grow near the margin of the streams it inhabits. Musk-Rats are most active at night, spending the greater part of the day concealed in their burrows dug out of the bank, consisting of a chamber with numerous passages, all of which open under the surface of the water. For winter quarters they build more elaborate houses of conical or dome-like form, composed of sedges, grasses, and similar materials plastered together with mud. As their fur is an important article of commerce, large numbers are annually killed, being either trapped or speared at the mouths of their holes.

The skull of the Musk-Rat is shown in Fig. 203 (p. 459); its structure is essentially Arvicoline, but the squamosals are greatly expanded, with a corresponding reduction of the parietal and interparietal, and the interorbital constriction of the frontals attains its greatest development. Fossil remains of Fiber occur in the North American Pleistocene.

Neofiber.[348]—This genus, while agreeing with Fiber in the characters of the skull and teeth, differs by the cylindrical tail, and the normal form of the feet, in which the toes are not bent laterally at an angle with the sole. The single species N. alleni, commonly known as the Round-tailed Musk-Rat, is found in Florida, and is much less completely aquatic in its habits than Fiber. Its colour is brown above, and silvery-white mixed with rufous below, the sides of the body gradually shading from brown to rufous, the forehead and the tip of the nose are black, while the tail is rufous mingled with black.

Subfamily Siphneinæ.—Includes two genera of Mole-like Rodents with an Arvicoline dentition, but with the body thoroughly adapted for a subterranean life, the limbs and tail being very short, and the external ears rudimentary. Both are Palæarctic.

Ellobius.[349]—The Russian E. talpinus, the typical representative of the genus, has short claws, and comes nearest to the Arvicolinæ. E. fuscocapillus is from Afghanistan.

Siphneus.[350]—This genus (Fig. 210) includes species inhabiting Northern and Central Asia, and is characterised by the great length of the claws of the manus. Remains of an existing species occur in the Pleistocene of the Altai, while an extinct one has been described from the Pliocene of North China.

Subfamily Deomyinæ.—Represented only by the under-mentioned genus, in which the bituberculate anterior and tricuspidate middle ridge of the first upper molar presents a condition intermediate between that obtaining in the Cricetinæ and that of the Murinæ.

Deomys.[351]—Externally as in Mus. Pollex with a narrow nail; hind feet elongate. Infraorbital vacuity of skull triangular, not narrowed below. Upper incisors with a pair of minute grooves. First upper molar with seven distinct tubercles, of which three are placed on the middle ridge, and two on each of the others. One species, D. ferrugineus, from the Lower Congo, an animal about the size of the Common Mouse.

Subfamily Murinæ.—Molars rooted and tuberculated; those of the upper jaw with three longitudinal rows of tubercles (Fig. 206, A).

This group includes the true Rats and Mice, and may be regarded as more specialised than the Cricetinæ. All the members of the group closely resemble one another, and are light and active, with large ears, bright eyes, and long and scaly tails. Their coloration, in conformity with the fossorial and nocturnal habits of most of the forms, is sombre, and their movements are remarkably agile and graceful.

Mus.[352]—Incisors narrow, without grooves. Structure of molars as in Fig. 206, A (p. 463). Incisive foramina of skull long; coronoid process of mandible well developed. Ears and eyes large; muzzle naked at the extremity. Fur soft, in some cases intermingled with spines. Pollex with a short nail in place of a claw. No cheek-pouches. Tail long, nearly naked, with rings of overlapping scales. Vertebræ: C 7, D 13, L 6, S 4, C 26-32.

This genus is the largest in the whole mammalian class, comprising not less than 130 species, ranging over the whole of the Old World, with the noteworthy exception of Madagascar. On the whole, the species are more numerous in tropical than in temperate regions, and very few occur in cold countries. Many of the species living in warm climates have flattened spines mingled with the fur; these spines being shed in winter, when a warmer covering is necessary, and replaced by hair. Five species occur in England, which are briefly noticed below; and it may be observed that none of the species are much larger than M. decumanus or smaller than M. minutus. As a rule the habits of the species are similar to those of the English forms, but a few are arboreal, while others again, like the one represented in Fig. 211, are aquatic. The earliest known representatives of the genus (excluding Acanthomys gaudryi of the Lower Pliocene Pikermi beds of Attica) occur in the Pleistocene of Europe.

The Brown or Norway Rat (M. decumanus) is a heavily built animal, growing to 8 or 9 inches in length, with a bluff rounded head, small ears (Fig. 212, A), and a comparatively short tail, which is always shorter than the head and body combined, and generally not longer than the body alone. The colour is a uniform grayish-brown above and white below, the ears, feet, and tail being flesh coloured. Black varieties, which are often mistaken for true Black Rats, are by no means rare, but the differences in size and proportions form a ready means of distinguishing the two. The Brown Rat is believed to be a native of Western China, where a race (M. humiliatus) has been discovered so like it as to be practically indistinguishable. Both this, and the next species agree in their predaceous habits, omnivorous diet, and great fecundity. They bear four or five times in the year from four to ten blind and naked young, which are in their turn able to breed at an age of about six months; the time of gestation being about twenty days.

The Black Rat (M. rattus) is a smaller and more lightly built species, generally not more than 7 inches in length, with a slender head (Fig. 212, B), large ears, and a thin tail of about 8 or 9 inches in length. The colour is usually a glossy bluish-black, somewhat lighter below; but in the tropical variety described as M. alexandrinus the general colour is gray or rufous, and the belly white. The disposition of the Black Rat is milder than that of M. decumanus, and the white and pied rats kept as pets mostly belong to this species. In many localities where it was formerly abundant it has been entirely superseded by M. decumanus, but it is said that in some parts of Germany it has been lately reasserting itself.

M. musculus, the Common House-Mouse, is, like the Brown Rat, originally a native of Asia, whence it has spread to all the inhabited parts of the globe. Its habits and appearance are too well known to need any description.

M. sylvaticus, the Wood or Long-tailed Field-Mouse, is very common in many parts of England, often taking to barns and outhouses for shelter during the winter. It is of about the same size and proportions as M. musculus, but of a bright reddish-gray colour, with a pure white belly.

M. minutus, the Harvest-Mouse, is the smallest of the European Mice, seldom exceeding 2½ or 3 inches in length. It is of a yellowish-red colour, with comparatively short ears and tail. It lives entirely away from human habitations, generally dwelling in grass or corn-fields, where it builds a globular nest of dried grass of the size of a cricket-ball, in which the young are nurtured.

Nesocia.[353]—General characters those of Mus, but the incisors and molars very much wider, and the tubercles of the latter more connected by transverse ridges, thus producing a laminated type of structure.

This genus has been placed by some writers in a distinct subfamily with Phlœomys, but Mr. O. Thomas regards it as so closely allied to Mus that even its generic separation may be open to question. It comprises several species, mostly spread over Southern Asia, ranging from Palestine to Formosa, and from Kashmir to Ceylon, but N. scullyi is found in Turkestan. The great Indian Bandicoot-Rat (N. bandicota) is the largest representative of the subfamily, often exceeding a foot in length. N. bengalensis is remarkable for possessing no less than eighteen mammæ. Fossil remains of Nesocia occur in the Pleistocene of Madras and in the Pliocene of Northern India; those from the first-named deposits being referable to existing species.

Golunda.[354]—Like Mus, but with a distinct groove down the front of the upper incisors. There are only three species, one from Western India, one from West Africa, and the other from Eastern Africa.

Uromys.[355]—Differs from Mus in having the scales of the tail not overlapping, but set edge to edge, so as to form a sort of mosaic work. There are about six species of Uromys, spread over the northern part of the Australian region from the Aru Islands to Queensland.

Chiruromys.[356]—Externally like Mus, but with the terminal portion of the tail without scales above, quite naked, transversely wrinkled, and prehensile. Scales of remainder of tail more or less pentagonal, and arranged in oblique diagonal series. Supraorbital vacuity of skull without projecting plate in external wall. Incisive foramina short and narrow; auditory bulla small. Upper molars very complex, with the tubercles (of which there are eleven in the first tooth) low, and distinctly arranged in transverse rows. Known only by C. forbesi, from mountains in New Guinea, which must be regarded as a specialised form very similar in outward appearance to Uromys cervinipes.

Hapalotis.[357]—Hind limbs elongated. Incisive foramina very large. No coronoid process to the mandible. This genus is confined to Australia, where there are about fifteen species known. They are pretty little animals, with long ears and tail, and in many respects resemble the Jerboas, whose place they seem to take in the sandy Australian deserts. Remains of H. albipes occur in the Pleistocene of New South Wales.

Mastacomys.[358]—Like Mus, but with the molars remarkably broadened, and with only four mammæ. The single species of the genus is as yet only known from Tasmania, though it has been found fossil in New South Wales; it is somewhat similar in size and general appearance to the English Water-Vole, but has much longer and softer fur.

Acanthomys.[359]—Fur almost entirely composed of flattened spines. Teeth and skull as in Mus, but the coronoid process of mandible very small. There are six species of Spiny-Mice known, all of about the size of the Common Mouse. They are found in Syria, Palestine, and Eastern Africa as far south as Mozambique. A. dimidiatus presents the appearance of a little Hedgehog when its spines are erected; it inhabits the stony deserts of Arabia Petræa and Palestine, and feeds on bulbs. A fossil Mouse (A. gaudryi) referred to this genus occurs in the Lower Pliocene of Attica.

Echinothrix.[360]—A very remarkable rat with an extremely elongated muzzle, all the bones of the face being much produced. The incisors are faintly grooved. The only species is E. leucura, an animal of about the size of the Brown Rat, with its fur thickly mixed with spines. It is found in Celebes.

Typhlomys.[361]—This genus is represented by a single species from China, which resembles a House-Mouse in size and general appearance, but has smaller ears, while the eyes are so reduced in size as to be totally concealed by the long eyelashes.

Cricetomys[362] and Saccostomus.[363]—These two African genera have been—from the presence of cheek-pouches—usually placed in the neighbourhood of Cricetus, but their molars are of the Murine type. Cricetomys is said to have grooved upper incisors, and is represented only by C. gambianus. There are two species of Saccostomus.

Pithechirus.—A small Rodent from Sumatra and Java described under this name is a true Mouse, having nothing to do with Chiropodomys, to which it has been compared.

Family Spalacidæ.

Mole-like forms, with very small or rudimentary eyes and ear-conchs, large claws, and short or rudimentary tail. Form cylindrical. Incisors large; premolars present or absent; molars rooted, with re-entering enamel-folds; palate narrow.

Subfamily Spalacinæ.—Angular part of the mandible arising from the lower edge of the socket of the lower incisor. No premolars.

Spalax.[364]—Represented by the great Mole-Rat (S. typhlus) of South-Eastern Europe, in which the eyes are completely covered by the skin.

Rhizomys.[365]—Eyes uncovered, although very minute; small naked ear-conchs; and a short partially hairy tail. Includes several species from Northern India, Tibet, China, Burma, Malaya, and Eastern Africa. A fossil species occurs in the Pliocene Siwaliks of Northern India.

Subfamily Bathyerginæ.—Angular part of the mandible arising from the side of the socket of the lower incisor. Premolars absent or present. Confined to the Ethiopian region.

Bathyergus.[366]—Upper incisors strongly grooved; p ¹⁄₁, m ³⁄₃; no ear-conchs; very powerful claws. One species (B. maritimus), from South Africa, attaining a length of about 10 inches.

Georychus[367] and Myoscalops.[368]—Upper incisors without grooves. Georychus, with some half dozen species, generally has p ¹⁄₁; Myoscalops, with one species, usually has p ³⁄₃, and the second toe of the foot is the longest. In Georychus the premolar may be wanting, and some examples of Myoscalops have only two teeth of this series.

Heterocephalus.[369]—Small and nearly naked forms, with small head, small eyes, no ear-conchs, moderately long tail, and powerful fore feet provided with a pair of large pads; p ⁰⁄₀, m ²⁻³⁄₂₋₃. Two species. These very remarkable little Rodents are regarded by Mr. O. Thomas as very closely allied to Georychus, but specialised, and, so to speak, somewhat degraded for a purely subterranean life, for which their hairless body is peculiarly adapted. They are found in Somali-land, where they burrow in the sandy soil.

Family Geomyidæ.[370]

Terrestrial or fossorial forms, with large cheek-pouches opening on the cheeks outside the mouth. Squamosal much expanded, and the jugal extending forwards to the lachrymal. P ¹⁄₁; molars rooted or rootless, with transverse laminæ. Nearctic and Neotropical regions.

Subfamily Geomyinæ.—Incisors broad; mastoid not appearing on the top of the skull; eyes small; ear-conch rudimentary; limbs short, subequal. Habits fossorial.

Geomys.[371]—Upper incisors deeply grooved. The common North American Pouched-Rat or “Pocket-Gopher” (G. bursarius) inhabits the plains of the Mississippi and lives in burrows. Several other species are recognised from the Southern United States, Mexico, and Central America. The genus is represented in the Pleistocene and Pliocene of the United States.

Thomomys.[372]—Upper incisors plain. Represented by two species, with numerous varieties found all over Canada and North America west of the Rocky Mountains. Remains referred to an existing species occur in the Pliocene of Oregon. Entoptychus, from the Miocene of the United States, is an allied genus, with broad incisors and rootless molars.

Subfamily Heteromyinæ.—Incisors narrow; mastoid appearing largely on the top of the skull; eyes and ears moderate or large; hind limbs and tail elongated. Habits terrestrial.

Dipodomys.[373]—This genus is characterised by the rootless molars. It is best known by D. phillipsi, the Kangaroo-Rat of the desert regions east of the Rocky Mountains, having habits like those of the Jerboas. The typical forms have four toes in the pes; but in others, which it has been proposed to separate as Dipodops, there are five: D. ordi and D. agilis belong to the latter group.

Perognathus[374] and Heteromys.[375]—In both these genera, which are represented by species of very small size, the molars are rooted; the latter being distinguished by the presence of flattened spines mingled with the fur, and having species ranging into South America. According to Dr. C. H. Merriam the forms described as Cricetodipus are not separable from Perognathus; while Dr. Coues considers that Saccomys was founded upon a species of Heteromys. Pleurolichus, from the Miocene of the United States, is regarded as an extinct genus allied to Heteromys.

Family Dipodidæ.

Terrestrial forms usually with four upper cheek-teeth, and typically with the following characters. Incisors compressed; molars with transverse enamel-folds; infraorbital vacuity of skull (Fig. 7, p. 37) large and rounded; jugal ascending in front to the lachrymal; and the mastoid part of the auditory bulla usually very large.

Subfamily Sminthinæ.—Molars rooted; p ¹⁄₀, m ³⁄₃. Skull with the infraorbital vacuity widest below, and the incisive palatal foramina long. Limbs short. Palæarctic.

Sminthus.[376]—Represented by the Rat-like S. vagans from Northern Europe and Asia, in which the ears are rather long and pointed, the tail is covered with short hairs and nearly as long as the body, while the molars present a somewhat complicated pattern. This genus has generally been regarded as an aberrant member of the Muridæ, but was transferred in 1887 to the present family by Dr. H. Winge.

Subfamily Zapodinæ.—Molars rooted; p ¹⁄₁, m ³⁄₃; cervical vertebræ free; hind limbs elongated; metatarsals separate; hind feet with five digits. Nearctic region.

Zapus.[377]—The American Jumping-Mouse (Z. hudsonianus) extends over almost the whole North-American continent from Labrador to Mexico.

Subfamily Dipodinæ.—Molars rooted; p ⁰⁻¹⁄₀₋₁, m ³⁄₃; cervical vertebræ more or less ankylosed; hind limbs elongated; metatarsals united; hind feet with only three functional digits. Palæarctic and Ethiopian regions.

This subfamily includes the true Jerboas, and contains three genera: Dipus[378] with three toes, and Alactaga[379] and Platycercomys[380] with five, the outer two not reaching to the ground. The latter is distinguished by the absence of premolars, and comprises many species extending from Siberia to Nubia.

Remains of the existing Alactaga decumana[381] occur in the Pleistocene of Germany, and those of Zapus hudsonianus in the corresponding strata of the United States. Platycercomys has been recorded from the Pleistocene of Northern Asia.

Subfamily Pedetinæ.—Molars rootless; cervical vertebræ free; hind limbs elongated; metatarsals separate; hind feet with four digits. Vertebræ: C 7, D 12, L 7, S 3, C 30. Ethiopian region.

Pedetes,[382] the Cape Jumping-Hare (P. caffer), by far the largest species of the family, extends from Mozambique and Angola to the Cape of Good Hope.

Section Hystricomorpha.

Skull (Fig. 213) with a stout zygomatic arch; jugal not supported below by a continuation of the maxillary zygomatic process; infraorbital vacuity large; mandible with the angular part arising from the outer side of the bony socket of the lower incisor. Clavicles perfect or imperfect; fibula distinct. One premolar in each jaw.

Family Octodontidæ.

Clavicles complete. Skull with long incisive foramina extending into the maxillæ; and usually an inferior angle to the jugal. Molars with external and internal enamel-folds; p ¹⁄₁, except in Ctenodactylus. Mammæ placed high up on the sides of the body. Confined to the Ethiopian and Neotropical regions, with the exception of one species of Echinomys which ranges into Central America. Habits mostly terrestrial, but occasionally fossorial or natatorial.

Subfamily Ctenodactylinæ.—Molars semi-rooted; jugal as in Dipodidæ; the two inner toes of the hind feet with a horny comb and rigid bristles. Ethiopian region.

Ctenodactylus.[383]—Represented only by C. gundi from North Africa, on the borders of the Sahara. Has no premolars; each foot has four digits; the hind limbs are rather longer than the fore; the ears small; and the tail reduced to a stump. This animal is about the size of the Water-Vole, and dwells on rocky ground, its habits being diurnal. The peculiar comb-like inner toes are employed for dressing the fur.