16. Anguidae.—A small family, chiefly American, but with a few species in Europe and the Indian region; all the species have large, overlapping scales with osteoderms beneath them and the tongue is retractile into a basal sheath. Gerrhonotus of North and Central America and Diploglossus of the West Indies, Central and South America are genera with well developed, pentadactyle limbs; Ophisaurus has the limbs reduced to a pair of small sty lets on each side of the vent and has a peculiar distribution, one species occurring in the United States, another in India and Burma, and the third in Southern Europe and Morocco. The European species (0. opus) is the "Scheltopusik" or "Glass snake," the latter name bestowed on account of the extreme fragility of its tail, which, if the creature is roughly handled, breaks into several fragments. The American species has a similar habit and the same vernacular name. Anguis, another genus, has no external rudiments of limbs; its sole species, fragilis, known in England as the Slow-worm or Blind Worm a snake-like creature frequenting grassy banks and ditches and is remarkable as one of the few animals which preys almost ex clusively on slugs.
17. Xenosauridae.—With but a single species Xenosaurus gran dis from the mountains of Mexico, has four well-developed limbs, the body covered with small granules and tubercles and a distinct fold of skin along the flanks.
20. Agamidae.—Old World lizards with broad, thick tongues, usually with small scales, even on the head, without osteoderms, and with the teeth usually differentiated into incisors, canines and molars; the majority are insectivorous but a few are almost exclusively vegetarian. Agama, common throughout the drier parts of Africa, and South-west Asia is a ground-living genus, and as a rule its members are dull brown creatures with irregularly arranged patches of enlarged scales which may form tufts of spines in the neck region; the males, of many species, however, exhibit brilliant patches of red and blue. Phrynocephalus is an Asiatic genus of desert and steppe-dwelling forms all with very depressed bodies and coloured with neutral tints of browns, greys, dull reds and yellows. The Frilled Lizard (Chlamydosaurus) of Australia is another inhabitant of dry districts and possesses a remarkable erectile collar; this is a fold of skin supported by cartilaginous rods like the ribs of an umbrella and when not in use is folded, cape-like, about the shoulders ; when the lizard is disturbed, it first seeks safety in flight, running swiftly on its hind limbs with the body inclined forwards and the long tail raised as a counterpoise, but if unable to escape, it turns at bay and tries to frighten the pursuer by erecting the frill and opening the mouth; the saffron-yellow interior of the mouth contrasting with the green and brown of the frill is impressive, but actually the chief means of defence lies in the powerful, whip-like tail. An
other common Australian species is the Bearded or Jew Lizard (Amphibolurus barbatus), a rather large species with an array of spiny scales under the throat and fringing the head behind the ears. Physignathus which ranges from Australia to Tonkin is largely aquatic, frequenting the banks of streams and taking readily to the water if disturbed. Arboreal forms are represented in the Indo-Malayan region by such genera as Calotes with very compressed bodies and long tails ; the species of this genus have a crest of large, blade-like scales along the back and possess con siderable powers of colour change, which, as in the Chameleons, are often called into play more by psychical disturbances and physical conditions than in relation to the background; the Blood sucker (C. ophiomachus) of S. India and Ceylon has aquired its name from the blood-red head and neck which it acquires when excited. Most remarkable of the arboreal Agamids are the Flying Lizards (Draco) of the Malayan region, which, like their mama lian analogues, the Flying Lemurs and Squirrels, have a fold of skin along the sides of the body which functions as a "plane" and enables them to make gliding flights from branch to branch or from tree to tree ; these wings, supported by 5 or 6 elongate ribs, are often so gorgeously coloured that the animals in flight resem ble gaily coloured butterflies, but the body of the animal is usually of a sober hue and, when the wings are folded at the end of a flight, the change is so abrupt and deceptive that the animal itself seems to disappear. Herbivorous forms are represented by the Mastigures (Uromastix) of the dry regions of N. Africa and S. W. Asia, heavily built creatures with tails armed with whorls of large spines. Another Agamid of dry regions is the Australian Moloch (Moloch horridus) a deserticolour species which, like so many desert-dwelling animals and plants, has developed an armour of large spines; it is a small, squat animal with a short tail and is covered with relatively large spines which reach their greatest size on the head above the eyes. Bizarre ornamentation is ex hibited by a number of genera in the Indo Malayan region; Cera tophora of Ceylon has a horn-like prominence on the tip of its snout and Lyriocephalus, also of Ceylon, has the sides of the head raised into bony ridges like those of some Chamaeleons and has the tip of the snout ornamented with a large, globular boss.