A marked exception to the smooth-scaled, water-loving snakes is the African viper, known as the ‘River Jack’ from its partiality to water. _Vipera rhinosceros_, from the spinous scales which have the appearance of horns on its nose, is allied to those described in the 18th chapter. Though not strictly a water snake, it much frequents it, and glides through it with ease, the more remarkable because, in common with those other ‘horned vipers’ of Africa, it has a short, insignificant little tail, which can be of little use as a propelling power. Altogether, it is one of the ugliest and most ferocious-looking of the whole serpent tribe, with a thick, heavy body, a dingy, rough exterior, and strongly-carinated scales. Excepting in colour, and a more horizontal inclination of its horns, it is not unlike the _V. nasicornis_ of the coloured illustration, chap. xviii. While all the _Homalopsidæ_ or true fresh-water snakes are innocent, there are many other venomous kinds known as ‘water serpents,’ both in Africa and America. For example, the ‘water viper,’ or ‘water moccasin,’ _Cenchris piscivorus_, whose aquatic and fish-eating propensities were described in the chapter on Tails. This ‘thorn-tail’ viper has not, however, the nostrils of the true fresh-water snakes or _Homalopsidæ_. In Australia also are several poisonous species, known vernacularly as ‘water snakes;’ but strictly speaking, and on the authority of Günther, the true _Homalopsidæ_ are all non-venomous. To describe these more minutely from Günther, Krefft, and Dr. E. Nicholson, ‘they have a body moderately cylindrical, a tail somewhat compressed at the root, and more or less prehensile. Many of them have a distinctly prehensile tail, by which they hold on to projecting objects;’ and in times of storms and strong currents we can imagine the importance of this security to them. Their eyes, though prominent, are small, and thus less exposed to injury; and the nostrils, as already stated, are on the upper surface of the head, and provided with a valvule. Another peculiarity is that the last or back tooth of the maxillary bone is a grooved fang, a transitional tooth between an ordinary one and a fang; but there is no evidence of any poisonous saliva connected with it. Indeed, as we may repeat, Dr. Günther distinctly affirms that all the fresh-water snakes are harmless and _thoroughly aquatic_, though a few are occasionally found on the beach. They inhabit rivers and estuaries, feeding on fish, and rarely coming to land; some of them frequent brackish waters, and even enter the sea. These latter in their organization approach the true marine serpents. One Indian example, _Hydrinus_, is semi-pelagic. They are all viviparous, producing their young in the water; and they belong to the tropical or semi-tropical regions. In Australia they are found only in the far north; but in America some so-called ‘water snakes,’ which spend most of their time in the water, frequent rivers which are frozen