8. Gerrhosauridae.—A small family confined to southern Africa, and Madagascar. As in the Skinks, the scales are large and im bricating with osteoderms beneath them but there is often a band of small scales between the armour of the belly and the back and, when the body is not distended, this region has the form of an inturned fold. Gerrhosaurus of S. Africa and Zonosaurus of Madagascar have well-developed limbs but the African Tetradac tylus shows various stages of limb-reduction, the most degenerate form, T. africanus, having mere stumps.
9. Lacertidae.—The true lizards of the Old World, but not found in Madagascar or the Australian region, their northern limits coincide almost with the edge of the area of permanently frozen sub-soil but they are most numerous in the African region. All are terrestrial with well-developed pentadactyle limbs and long, fragile tails; the scales of the body as a rule are small, but the head is covered with large, regularly arranged shields beneath which are osteoderms. The majority of the European lizards belong to this family and to the genus Lacerta of which 2 species occur in the British Isles. The common Lizard (L. vivipara) has a wide range through northern Europe and is fairly plentiful on heaths and commons throughout Great Britain; in Ireland its distribution is irregular. It is a small creature, rarely more than 5 or 6 inches in total length, brown or olive in colour with darker streaks and small lighter round spots on the flanks ; like the majority of lizards it feeds chiefly on insects and normally it is ovoviviparous though there are records of specimens having laid eggs. The other British lizard is the Sand Lizard (L. agilis) which, despite its scientific name, is a more heavily built, larger and less nimble species than the preceding; it is rare in England, being confined to a few isolated localities in Lancashire and the south, though common on the continent. Females are brown with rows of darker and lighter spots and patches but the ground colour of the males is a brilliant emerald green with an irregular dark stripe down the middle of the back and small, ocellar, whitish spots. The Green Lizard (L. viridis) is a much larger species, usually of a vivid green colour with or without small black dots, and is fairly common throughout France and Central Europe. The com monest and most variable species in Europe is the Wall Lizard (L. muralis) ; it abounds throughout the centre and south and on the islands of the Mediterranean where almost every tiny islet has its own peculiar colour variety, often endowed with the rank of a separate species. On the mainland, too, the colour varieties are almost endless but all intergradations are known and it is impossible to tell whether we have to deal with a number of species which freely hybridise or with one or two which are very variable. Another very beautiful southern European species is the Eyed Lizard (L. ocellata) which reaches a length of i8 to 20 inches; the colour is brilliant green with rows of blue, black bordered, eye-like spots along the flanks. Acanthodactylus of South-west Europe and N. Africa has the fingers and toes edged
with a fringe of elongate scales, a modification which enables the animals to run over the surface of soft sands. Cabrita in India has a transparent disc in the lower eyelid and Ophisops which ranges from N. Africa to India has a similar modification but has the lower eyelid fused to the upper as in the skink Able pharus.
10. Teiidae.—An American family whose typical members su perficially resemble the Old World Lacertids ; the tongue is always narrow, deeply bifid and often retractile into a basal sheath like that of a snake ; the majority are South American but a few have established themselves as far north as the southern United States. Some are arboreal, others strictly terrestrial and a number of small forms have the limbs reduced in correlation with burrowing or semi-burrowing habits. The Teju or Teguexin (Tupinambis teguixin) of the tropical parts of America is the largest species and in size and general habitus as well as habits resembles the monitors; it reaches a length of 3 to 4 feet most of which, how ever, belongs to the whip-like tail. Callopistes of Peru and Chile is another large monitor-like creature which digs branching bur rows often several yards long. Crocodilurus of the Amazon basin is characterised by a double, crocodile-like crest along the tail and Dracaena another large species of the same region has the lateral teeth modified to form large oval crushers in correlation with a herbivorous diet. More Lacerta-like are the numerous species and varieties of Ameiva and Cnernidophorus which extend throughout tropical America, the former reaching the West Indies and the latter extending into the southern United States where they are known as the Race Runners. Frequenting dry and sandy localities they move with prodigious speed and are usually charac terised by a number of longitudinal yellow stripes on a dark back ground, Ameiva ameiva exhibits almost as many local races and intermediates as the European Wall Lizard. In the smaller forms there is progressive reduction of the limbs and development of a window in the lower eyelid; Alopoglossus of Ecuador and Peru has a few enlarged semi-transparent scales on the lower eyelid; Pantodactylus of Southern Brazil and N. Argentina is a rather elongate form with an undivided transparent disc and Gymnoph thalmus and Micrablepharus have, like some skinks and lacertids, the transparent lower eyelid fused with the upper. Anadia of Central America and Ecuador is very elongate but with the limbs pentadactyle ; Scolecosaurus is serpentiform with three or four clawed fingers and toes and burrows in humus and rotten wood, feeding principally on termites. Bachia of northern South Amer ica exhibits the greatest degree of degeneration in the family; the body is elongate and serpentiform, the eye minute but still equipped with functional eyelids, scales are no longer granular or overlapping but are squarish and arranged in regular longitudinal and transverse rows like those of the Amphisbaenids, fingers are reduced to clawless tubercles or quite absent and the hind-limbs may have but a single toe.