Head short, depressed, somewhat abruptly deflexed from the vertex—the scales flat, those of the suprà-orbital arch being numerous, and less regular than in most other species. Between the labial scales, and the long infra-orbital plate is a single series of rounded scales.^[1] The scales of the temples are rather large, somewhat rounded, slightly imbricated, and a few of the posterior ones having the vestige of an obtuse carina. The ear is rather small, the anterior margin having two slightly prominent scales towards the lower part.

The body is depressed; the tail moderately long, thick and slightly four-sided at the base, becoming much smaller and round towards the middle. The scales of the sides of the neck are small and granular; those of the upper parts of the body small, rhomboidal, rounded posteriorly, loose, much imbricated, and with an extremely low and inconspicuous carina. They are arranged in about twenty-two longitudinal series. Those of the sides are larger and quite smooth. The scales of the whole under part of the throat and belly are rhomboidal, smooth and much imbricated; a very few towards the sides of the abdomen are slightly notched at the apex. The under surface of the anterior and the hinder surface of the posterior extremities are covered with very fine granular scales; those of the upper surface of the members being rhomboidal, smooth, but slightly carinated and obtuse. The tail is covered with small rhomboidal scales which are considerably imbricated and distinctly carinated. The scales of the upper surface of the toes are smooth; those on their sides uni-carinated, and those beneath tri-carinated and broad.

The general colour of the upper parts is a yellowish grey, with black markings, which have somewhat the character, as Mons. Bibron observes, of Arabic letters. On the neck and back these markings are disposed in four longitudinal series; and there are small linear markings on the upper part of the shoulders and thighs. The tail is similarly marked, the under parts are whitish, with brown lines and spots.

This species is not found amongst the reptiles obtained by Mr. Darwin, but as it has never been figured, it appeared very desirable that this opportunity should not be lost. I am indebted to the great kindness of my friend M. Bibron for the loan of the only specimen which I have seen, and from which the accompanying figure is taken. It formed part of the zoological collections obtained by Mons. D’Orbigny for the French Museum.

Capite brevi, squamis neque imbricatis nec carinatis, tecto; auribus margine anteriore tridentato; serie unicâ squamarum supralabialium; squamis temporum magnis, rotundatis, imbricatis; colli (et præcipuè plicæ) crassis, elevatis; facie posteriore femorum omninò granulosâ; squamis nonnullis ad latera abdominis gulæque emarginatis; maculâ transversè; oblongâ, nigrâ, suprà regionem scapularem.

Habitat, Coquimbo, Chile.

Description.—Head short, the muzzle rounded, rather obtuse; scales of the upper part of the head somewhat convex, smooth; a single line of scales between the labial and orbitar; ears rather large, the anterior margin having three rather prominent scales, the middle one being the largest. Temporal scales somewhat large, smooth, rounded, and imbricated, those towards the upper part slightly carinated; those of the sides of the neck thick and elevated, those on the fold being rather acutely prominent; scales of the back carinated, the carina terminating in an acute point; a few of the scales at the sides of the abdomen and throat notched; the remainder of the scales of the under parts rhomboidal. The scales about the axilla and around the base of the shoulder are granular and very small, as are those of the posterior surface of the thighs, on which part there are no imbricated scales as in Tr. Fitzingerii. The tail is round, excepting at the base where it is slightly flattened; it is moderately long and slender. The anterior extremity placed against the side does not reach to the thigh; the posterior similarly placed reaches to the shoulder. The colour of this species is yellowish grey above, with a yellowish longitudinal line on each side the back, and two rows of black spots each margined with yellow behind. There is a large and distinct oblong black mark on the region of the scapula, from which circumstance the species takes its name. On the posterior surface of the thighs, towards the upper part, are three or four black dots placed in a line. The under surface is yellowish white with dark grey dots and lines under the chin and throat.

This species was first described by Weigmann, and subsequently by M. Bibron, from specimens obtained by Gaudichaud from Coquimbo, at which place the single specimen brought home by Mr. Darwin was also obtained.