The general appearance is too misleading for the classification of the Lacertae. E. D. Cope (_Proc. Ac. Philad._, 1864, pp. 224 et seq. and _Proc. Amer. Ass._ xix., 1871, p. 236, &c.) therefore relied upon more fundamental characters, notably the presence or absence of osteoderms, the formation of the skull, the teeth and the tongue. G. A. Boulenger (_Ann. Nat. Hist._ 5, xiv., 1884, p. 117, &c.) has further improved upon the then prevailing arrangements, and has elaborated a classification which, used by himself in the three volumes of the catalogue of lizards in the British Museum, is followed in the present article with slight alterations in the order of treatment of the families. In the following diagnoses of the families preference is given to such characters as are most easily ascertained. The 17 "families" fall into 4 or 5 main groups. Presumably the presence of osteoderms and of complete cranial arches are more archaic than their absence, just as we conclude that limbless forms have been evolved from various groups possessed of fully developed limbs. _Zonuridae_ and _Anguidae_ assume a central position, with _Agamidae_ and _Iguanidae_ as two parallel families (not very different from each other) of highest development, one in the Old World, the other in America. _Xenosaurus_ seems to be an offshoot intermediate between the _Iguanidae_ and the _Anguidae_; a degraded form of latter is perhaps _Aniella_ of California, whilst _Heloderma_ and _Lanthanotus_ are also specialized and isolated offshoots. A second group is formed by the few American _Xantusiidae_, the numerous American _Tejidae_, and the burrowing, degraded American and African _Amphisbaenidae_. A third group comprises the cosmopolitan _Scincidae_, the African and Malagasy _Gerrhosauridae_ which in various features remind us of the _Anguidae_, and the African and Eurasian _Lacertidae_ which are the highest members of this group. _Anelytropidae_ and perhaps also _Dibamidae_ may be degraded Scincoids. The _Varanidae_ stand quite alone, in many respects the highest of all lizards, with some, quite superficial, Crocodilian resemblances. Lastly there are the few _Pygopodidae_ of the Australian region, with still quite obscure relationship. Family 1. _Agamidae._--Acrodont; tongue broad and thick, not protractile; no osteoderms. Old World.