SPECIES OF MAMMALS OF THE PACIFIC AREA 113 the house mouse, the body is considerably heavier; its total length is about five and one-fourth inches, of which the tail is about two inches. It is known from Hondo and Shikoku Islands, Japan.
Old World Rats and Mice. Family Murid^ Although the rats and mice of this family belong to the Old World, some of them have spread wherever men are found. Rats and mice of American origin, some of which occur in the Galapagos Islands near the coast of South America, together with the northern voles and lemmings of both hemispheres, belong to a different family, the Cricetidae (see p. 119). The only rodents that occur in the South Pacific area between Celebes and the one-hundredth degree west latitude are Old World rats and mice. This is a complex and varied group, basic differences of which reside chiefly in the structure of the skull and teeth. Many of them look like common house rats. Two subfamilies occur on the islands between the Malay Peninsula and Australia ; only one of these subfamilies, the typical rats, is found east of the Solomons.
Typical Rats and Mice. Subfamily Murine The cheek-teeth of most of these rats are simple, their cusps forming parallel transverse ridges, three ridges on the first molar, two on the other two. Before it becomes worn each ridge consists of three cusps, the central one slightly larger than the outer and inner ones. Although this seems a rather small feature, it has been characteristic of the family for a long period of time.
The House Mouse (Mus) is so well known that it may be thought unnecessary to describe it. Most specimens found between the Malay Peninsula and the Marquesas Islands are slightly more reddish than the house mice of the United States and western Europe; east of this region and north of it the mice are the same as at home. Adult house mice vary from
114 MAMMALS OF THE PACIFIC WORLD about seven and one-half to eight and one-fourth inches in total length, of which slightly more than half is tail. Two small mice are about the same size as the house mouse and are not very unlike it.
The Wood Mouse (Apodemus) of Formosa, Japan, and the Kuriles, is a Eurasian type found from the British Isles to eastern Asia. The tail is long and nearly naked. Wood mice are yellowish brown above, white below, and have white feet. The Pygmy Tree Rat {Hceromys), found in North Borneo and Celebes, has the tail longer than the house mouse, and the first toes on front and hind feet are thumb-like and opposable. The Common Rats (Rattus) are world-wide in distribution. Three kinds of rats have been carried involuntarily by man during the last three hundred years to the ports of the Pacific, whence they have spread widely. The Norway or brown rat (Rattus norvegicus), which is the common house rat throughout the northern United States and Europe, is the largest of the three, measuring fifteen or sixteen inches long with the tail a little less than half of this ; the females are smaller. The brownish gray fur is coarse, and the ears small. The scales of the tail number about twenty-five to the inch. In the tropics this rat is usually confined to seaports. The black rat and Alexandrine or roof rat, color varieties of a single species (Rattus rattus), are even more widespread in the warmer countries. They are relatively large animals, sixteen or seventeen inches long, with the tail a little more than half this length. The tail scales are finer than in the Norway rat, and the ears are large, reaching to the middle of the eye when laid forward. The black rat is recognized by its color, but the roof rat is colored much like the Norway rat and many native ones. Wild races of Rattus rattus are known in the islands between the Malay Peninsula and Celebes ; east of this they are replaced by other species. The small rats commonly living in native houses on the islands are all members of the Rattus concolor group, which occur from the mainland of Asia to Hawaii and the Marquesas Islands. The
SPECIES OF MAMMALS OF THE PACIFIC AREA 115 size of these rats varies from nine to twelve inches in total length, the tail usually a little longer than the head and body. They were almost certainly carried to the various islands in native boats when men first settled Oceania. A number of related wild species are also to be found on the Greater Sunda Islands and the Philippines.
The Bandicoot Rats (Bandicota) are partly adapted for life underground, but to a far less degree than the bamboo rats, described earlier. The front claws are large, the muzzle short and broad. The incisor teeth are broad and the cusps of the molars soon wear down to form almost straight cross-ridges. The adults reach a large size — total length, eighteen or twenty inches, of which the tail is almost half. Bandicoot rats are found on the islands of Formosa, Sumatra, and Java, as well as on the mainland.
The Red Tree Rat (Pithecheir) of Java and Sumatra has long soft reddish fur, which extends for almost an inch on the base of the tail. The teeth have high cusps which remain distinct until old age. The size of this rat equals that of common house rats. The first toe of the hind foot is thumb-like and opposable, whence its scientific name meaning "ape hand." Shrew rats, with long wedge-shaped head and often velvety fur, are found on Java, Sumatra, Celebes, and the Philippines. The Shrew Rat {Mycteromys) of Java and Sumatra has teeth much like those of the house mouse, but the first molar is about one-third larger than the other two combined, and the lower incisor is longer than usual.
The Celebes Shrew Rats (Echiothrix and Melasmothrix) have unusual incisors, the upper ones short and weak, the lower ones long. The first species, larger than a house rat, has spiny pelage; the upper incisors are whitish rather than the yellow usual in rodents, and each has a distinct groove down the face. The cheek-teeth are very small. The second kind on Celebes is about eight and one-half inches in total length, with the tail less
116 MAMMALS OF THE PACIFIC WORLD than half of this ; the fur is velvety, blackish bay in color. Both are quite rare.
The Philippine Shrew Rat {Rhynchomys) is known only from the mountains of northern Luzon. Its total length is about fourteen inches, including the five-and-three-fourths-inch tail. The velvety fur is dull olive-gray. The upper incisors are white, short and weak ; the cheek-teeth minute and only two in number on each side. Its teeth suggest that it may feed only on softbodied insects and worms, but nothing is known of its habits and only a very few specimens have been taken. Giant Rats (Hyomys, Anisomys, Uromys), heavy -bodied and about two and one-half feet in length, occur in New Guinea. They are not closely related to one another but look much alike. The New Guinea mosaic-tailed rat (Uromys) also reaches northern Australia and the Solomon Islands. The smaller mosaictailed rats (Melomys), closely related to Uromys, are only eight to fourteen inches in total length. Like Uromys, they have nearly naked tails, the scales of which do not overlap but are set edge to edge. These rats (Melomys) are found from the Talaut Islands and the Moluccas to the Solomon Islands and Australia.
Many other rare and little-known rats with cheek-teeth of simple, Rattus-like pattern occur on the islands between the Malay Peninsula, the Philippines, and the Solomons. Certain Indo-Australian rats which look much like house rats have complex teeth, the patterns of the cross-ridges in the upper cheek-teeth trefoil-like rather than simple crescents or straight lines. Lenomys, which represents this group in Celebes, is about twenty or twenty-two inches in total length, with the tail about half of this. Mallomys of New Guinea is much larger, two to two and one-half feet in total length, with the tail about fifteen inches.
The Complex-toothed Tree Mouse (Chiropodomys) of Sumatra, Java, and Borneo is small, the different forms varying from about six inches to a foot in total length, with the tail
SPECIES OF MAMMALS OF THE PACIFIC AREA 117 usually longer than head and body. The first toe on its hind foot is opposable as in several other tree rats. The tree rats of this group {Pogonomys) found on New Guinea and adjacent islands have a prehensile tail, the tip of which curls upward. Two large Bushy-tailed Rats {Phlceomys and Crateromys) are found in the northern Philippine Islands : Luzon, Mindoro, and Marinduque. They are two feet or more in total length, with the tail about three-fourths of the head and body length. Their molars, especially those of Phlceomys, have cross-ridges of more simple pattern, not very different from those of the bandicoot rats.
The indigenous Australian rats are far more diversified than is generally realized. In addition to a number of distinct species of Rattus (allied to house rats), Australia contains a number of distinct genera fully as striking as are those characteristic of New Guinea.
Australian Native Mice (Pseudomys, Thetomys, Leggadina, Gyomys) are about the size of house mice — some even smaller. The color, depending on whether they live in forest or desert, varies from dark to very pale gray, with underparts whitish. They are distributed all over Australia.
The Broad-toothed Rat {Mastacomys) is a large, dark-colored, short-tailed species remotely related to other Australian rats. It is found only in Victoria and Tasmania. The Thick-tailed Rats (Laomys) are characterized by the pronounced swelling of their tails just beyond a very slender constriction at the base. They occur in central and northwest Australia.
The White-tailed Rat (Zyzomys) is about eight inches long, the tail four or four and one-half inches of this. The tail is white, more thickly haired than usual among rats and has a small tuft of hair at its end.
The Rabbit Rats (Mesembriomys) are very large rats with rather large ears and elongated feet. Several races occur. The over-all size is twenty to twenty-three inches, with the tail twelve
118 MAMMALS OF THE PACIFIC WORLD to thirteen inches long. They are found only in the north of Australia. The only other large rats of northern Australia are the mosaic-tailed rats (Uromys), already mentioned as having headquarters in New Guinea.
Lesser Rabbit Rats (Conilurus) are easily separated from the preceding. The color above is blackish brown or dark gray instead of reddish brown with touches of creamy buff. The underparts are white. In total length they are about fifteen inches, with a tail about eight inches. They are found in northern Australia ; one race has been recorded in the extreme south of New Guinea.
Nest-building Rabbit Rats (Leporillus) are soft-haired, gray rats with large ears and white feet, marked with darker gray in one species. They are noted for making large nests, which may reach a height of three feet and a diameter of four, by weaving twigs together, using a growing bush for the framework. Several entrances are provided. In the center is the brood chamber, lined with soft materials. These rats are limited to the southern parts of Australia.
Australian Kangaroo Rats {Notomys) superficially resemble the kangaroo rats of the western United States, although they belong to a wholly different family of rodents. The hind legs are similarly elongated and kangaroo-like, and the long tail bears a tuft of hair at the end. In one species a throat pouch is present. The size is small: the total length is from eleven to fourteen inches, with the tail occupying from six to nine inches. The distribution includes most of Australia.
Water Rats. Subfamily Hydromyin^ The Australo-New Guinean Water Rats {Hydromys, Leptomys, Pseudohydromys, and others) have basined cheek-teeth, with few cross-ridges, and the infraorbital canal of the skull is wide, not slit-like as in the other rats. With the exception of Leptomys and the newly discovered Baiyankamys of New Guinea, these rats have only two molars in each jaw. As the
SPECIES OF MAMMALS OF THE PACIFIC AREA 119 name water rats implies, most of the members of this subfamily are aquatic. Exceptions are a small species {Xeromys myoides) from Queensland, Leptomys and Paraleptoinys, and probably Baiyankamys from New Guinea. True water rats are found also on the adjoining islands, New Guinea, New Britain and Kei, Aru and D'Entrecasteaux Islands, in addition to Australia. Celcenomys, Chrotomys, and Crunomys of Luzon — the last also in Mindanao, the Philippine Islands — are thought also to belong with the water rats. The molar teeth of Chrotomys are basined like Hydromys but they are three in number instead of two. Chrotomys is strikingly marked with a bright buff stripe from head to rump, bordered by black. Crunomys agrees with the common rats in tooth pattern, but the flattened shape of its skull suggests modification for life in water. Celoenomys is slaty gray ; it agrees with Hydromys in having only two cheekteeth on each side above and below and in the basined character of the teeth. These Philippine rats may be distantly related to the Australian forms or the resemblances may indicate convergence.
Voles, American Rats and Mice Family Cricetid^ The voles of the northern hemisphere and the rats native to the western hemisphere differ from true rats by having only two rows of cusps on the upper molars, instead of three. When the teeth wear down, these cusps form a more or less distinct zig-zag pattern, instead of cross-ridges. Although this difference seems small, it has characterized the two groups for millions of years.
The Red Lemming (Lemmus), which is probably to be found on the landward islands of the Aleutians, is a small, thick-set rodent with short hairy tail, small ears, and long, soft fur. The body color is rusty, grizzled on the head and shoulders. Locally this lemming may become abundant, but over much of its range it is scarce, at least during certain years. It is a close relative
120 MAMMALS OF THE PACIFIC WORLD of the famous Norwegian lemming which during its years of abundance makes great migrations, often ending in what looks like mass suicide, plunging into the sea and swimming out until drowned. The migrations of our lemmings are less well known and less extreme, but they have a similar cycle of alternating abundance and scarcity. The total length of this vole is about five inches, of which the tail is about one-half inch, excluding the hairs.
The Collared Lemming {Dicrostonyx) may also occur on the Aleutians nearest the mainland. It is colored gray, darker or black down the middle of the back, and has a reddish collar. In winter it turns white and develops very large claws. It is about six inches in total length.
The Lemming Mouse (St/naptomys) may also be found on the Aleutians. It is dark gray. Its total length is a little less than five inches, and the tail, which lacks long hairs, measures about three-fourths of an inch. The upper incisors are grooved. The Meadovs^ Mouse (Microtus), often called vole, is found in Japan and the Kuriles. The tail is longer than those of its relatives described above, but measures less than two inches ; the total length of the animal is about five inches. The Red-backed Mouse (Clethrionomys) , found in the Kuriles and Japan, is about the size of the meadow mouse, but is usually characterized by a rusty band down the back, contrasting with the grayish sides. Its teeth are slightly different from those of the meadow mouse. As in the rest of the group described above the cheek-teeth have a strongly marked zig-zag pattern, but they are rooted.
On the Galapagos Islands, off Ecuador, there are several species of rats belonging to the genus Oryzomys, abundant in Central and South America, and closely related to our rice rats. They must have reached those islands by drifting on natural rafts, for they were there before men came to the Galapagos and had developed into distinct species. Since the distance involved is more than five hundred miles, their presence on these