[The family of the _Viperidæ_, or true Vipers, are peculiar to the Old World, inclusive of Australia, with the sole known exception of one species in Peru. They have generally a robust body, with non-prehensile tail; the head broad or thick, generally scaly above or incompletely shielded; the eye of moderate size, with vertical pupil, and they are at once distinguished from the _Crotalidæ_ by the absence of the pit below the eye. The scales are keeled except in one genus (_Acanthopis_). For the most part, these reptiles inhabit exposed and arid situations, though perhaps all of them will take to the water on occasions, as does the common British Adder. They are divided, firstly, into those which have a depressed head, rounded on the sides, and covered with acutely-keeled scales. Some of these have large nostrils in the centre of a ring-like shield, edged with a large scale above. Such are the genera _Daboia_ in the warmer parts of Asia, and _Clotho_, which is peculiar to Africa--both genera are terrifically Venemous. The famous _Tic-polonga_ of Ceylon (_Daboia elegans_) is also widely diffused over India and Burmah. It is beautifully marked with three rows of white-edged, oblong, brown spots. Occasionally the spots forming the middle row are connected like the beads of a necklace, whence the name _Cobra monil_ (literally _Coluber moniliger_), applied to the young of this Viper by the Indo-Portuguese, and now corrupted into "Cobra de Manilla," which bears the reputation of being a highly poisonous Snake of diminutive size; it attains, however, to a length of nearly five feet, the tail then measuring about eight inches, with considerable thickness of body. It is nocturnal, and preys chiefly on Mice. In Burmah this formidable Viper is dreaded almost as much as the _Hamadryas_. It has been obtained in the Himalayas at an elevation of 5,500 feet, at Almorah, and elsewhere. Mr. Theobald has known one to kill a Bull-terrier in twenty minutes. The _D. xanthina_ is a second species of this form inhabiting Asia Minor. [Illustration: Fig. 21.--The Horned Puff-adder (_Clotho cornuta_).]