_Head-Shields._--Rostral as deep as broad, a little broader than deep, or slightly deeper than broad, reaching or nearly reaching the upper surface of the snout, and in contact with two or three apical shields. Upper surface of head covered with small subimbricate scales, which are all more or less distinctly keeled, or, rarely, smooth on the snout and forehead; seven to twelve longitudinal series of scales between the eyes (supraoculars included); two to four canthal shields, of which the anterior is the largest, and may be regarded as a supranasal. Supraocular narrow, usually broken up into two or more small shields. Twelve to eighteen scales round the eye; two or three series of scales between the eye and the labials; two or three vertical series of scales separate the preoculars from the nasal, which is single and often strongly hollowed out, and usually partially fused with the naso-rostral. Upper labials nine to twelve, usually fourth and fifth below the eye. Temporal scales keeled. Four or five lower labials in contact with the single pair of chin-shields. _Scales_ in twenty-three to twenty-seven rows, usually twenty-five, with two apical pits, strongly keeled, those of the outer row smooth or feebly keeled. Ventral shields 151 to 177 in males, 153 to 180 in females; anal entire; subcaudals 42 to 51 in males, 38 to 49 in females. _Coloration._--Very variable. The typical form, which alone is represented in Europe, and was originally described from Cyprus, is grey, greyish-buff, or pale brown, above, with two dorsal series of darker spots, which may stand in pairs, alternate, or unite to form cross-bars, and a lateral series of large dark spots or bars. A more or less distinct dark band on each side of the head, passing through the eye and often extending to the neck; a dark bar or triangular spot below the eye, and usually another below the nostril. Lower parts pinkish-white, powdered with grey-brown, with or without dark brown spots; end of tail yellow. The ground colour of the young is pink or flesh-colour. In specimens from desert sandy regions in Asia and North Africa the markings may be very indistinct, the snake being of a nearly uniform pale buff. In the var. _mauritanica_, Guichenot, from Morocco and Algeria, the back has three series of very large dark brown or reddish-brown spots, separated by a network of the yellowish ground colour, or the middle series may be transformed into a wavy or zigzag band. The scales in this variety are usually in twenty-seven rows, instead of twenty-five (rarely twenty-three) as in the typical form. _Size._--This species, the largest of European Vipers, grows to a length of 4-1/2 feet.