A specimen from Ponte Carrega, near Genoa, preserved in the Genoa Museum, is remarkable as being of a dark olive-grey, with three series of black and yellow ocellar spots. It is further exceptional in having the scales in nineteen rows. A second specimen, from the same locality, with the normal number of scales, has some of the vertebral spots ocellar. Specimens with ocellar vertebral spots are found also in Sardinia and in Spain.
As in _T. natrix_, there occur, in the South of France, in Sardinia, in the Spanish Peninsula, and in North Africa, specimens with two light yellow or reddish lines along the back (Plate III., third figure), in addition to the usual markings (_C. aurolineatus_, Gervais, _T. chersoides_, Duméril and Bibron).
Melanism is rare in this species, only one specimen being known, from Nantes in Southern Brittany; uniform black, with the exception of a few white spots on the belly. A remarkable variety (var. _incertus_, Fatio), connecting this species with the preceding, occurs in Switzerland near Geneva. Not only is its coloration sometimes very similar to that of _T. tessellatus_, but it agrees with it in the scales being often disposed in nineteen rows instead of twenty-one, and in the presence of eight upper labials, fourth or third and fourth entering the eye; however, the frequent presence of ocellar spots on the sides, and the low number of ventral shields (147 to 151), show that it should be referred to _T. viperinus_.
_Size._--Rarely reaches a length of 3 feet in Europe, the largest specimens being from Sardinia. An Algerian specimen 3 feet 3 inches long is on record.
_Distribution._--France as far north as Southern Brittany, the Forest of Fontainebleau, and the Department Aube, the whole of the Spanish Peninsula and the Balearic Islands, Southern Switzerland, north and south of the Alps, Liguria, Piedmont, Corsica, Sardinia, and Sicily. In Africa in Morocco, Algeria, and Tunisia, penetrating into the northern parts of the Sahara.
In Liguria, Piedmont, and Ticino, _T. viperinus_ occurs alongside with _T. tessellatus_. It reaches an altitude of nearly 4,000 feet in the Alps.
_Habits._--Very much the same as in the preceding species, although slightly less thoroughly aquatic, large individuals being sometimes met with at some distance from water. Ponds and marshes are the favourite abode of the Viperine Snake, huge numbers being often found on the borders, diving into the water when disturbed. Frogs and toads, tadpoles, newts, fishes, and large earthworms, are its principal food when adult, the young feeding chiefly on batrachian larvæ, young fishes, and earthworms. A case is known of this snake having eaten a water-shrew (_Crossopus fodiens_). When a fish has been caught, it is usually eaten on land; in captivity dead fish are rather readily accepted, provided they be quite fresh. Some specimens bite when handled; others are as gentle as the Grass-snake.