_Head-Shields._--Rostral broader than deep, visible from above. Nasal divided, very rarely semidivided. Internasals at least as broad as long, trapezoid, shorter than the prefrontals. Frontal broader than the supraocular, once and one-third to once and a half as long as broad, as long as or a little shorter than its distance from the end of the snout, shorter than the parietals, not in contact with the preocular. Loreal deeper than long. One (rarely two) pre- and three (rarely two or four) postoculars. Temporals 1 + 2. Upper labials seven (rarely six or eight), third and fourth (or fourth and fifth) entering the eye. Four or five lower labials in contact with the anterior chin-shields, which are shorter than the posterior. _Scales_ with two apical pits, in nineteen rows, strongly keeled on the body, of outer row smooth or faintly keeled. Ventral shields 157 to 181; anal divided; subcaudals 50 to 88. [Illustration: FIG. 16 (after Sordelli)] _Coloration._--Very variable. We shall first describe the typical form, and then allude to the principal varieties and individual variations with which we are acquainted. Grey, bluish-grey, olive, or brown, above, usually with black spots or narrow bars on the back, and vertical bars on the sides; upper lip whitish or yellowish, with the sutures between the shields black; the preocular, and sometimes the postoculars, yellow in the young; a white, yellow, or orange collar on the nape, sometimes uninterrupted, more often divided in the middle, bordered behind by two black subtriangular or crescentic blotches, which usually meet on the median line; the bright collar often becomes faint, or even entirely disappears, in large females (Plate II., first figure); belly usually checkered black and grey or white, more rarely grey with small black spots, or entirely black. Iris dark brown or reddish-brown, with a golden circle round the pupil. This is the form found in England and Central Europe and in some parts of Southern Europe. In Jersey, in the Spanish Peninsula, and in Cyprus, the white or yellow collar, which is always present in the very young, soon disappears, and so does usually the black collar, which is either much reduced or entirely absent (var. _astreptophorus_, Seoane). Some large specimens from the Spanish Peninsula are uniform olive, without any markings. Another variation (Plate II., third figure), rare in France, but common in Italy, South-Eastern Europe, and Asia Minor (var. _persa_, Pallas; _bilineatus_, Bibr.; _murorum_, Bonap.) has the collar well marked, though widely interrupted in the middle, and a white, yellow, or orange streak extends along each side of the back, which may bear the usual black markings in addition. In some specimens from Austria and Corfu (var. _subfasciatus_, Werner) the belly is white, with black bars occupying the free edge of each ventral shield.