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Show 4 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. PnocTOTRETUS GRACILIS. N .S. PLATE I.-FIG. 2. Cm-pm·e g1·acili: capitis squamis lcevibus, non imbricatis: aurium margine ante1·iore minute bi-l1·identato: collo vix plicato, squamis imbricatis: serie unicd squamarun supralabialium : femorum facie posteriore omnino granulosa. Habitat, Port Desire, Patagonia. Mr. Darwin, MS. DESCRIPTION.-This new species is more slender and graceful in its general form than any other of the genus, not excepting Pr. tenuis, which in its general proportions it considerably resembles. The head is rather short, the anterior portion including the eyes being nearly an equilateral triangle. The muzzle is rounded. The scales of the head flat, rather large, consisting behind the nose of three series of 2, 3, 3, and 2, mostly hexagons. The nostrils are small and perfectly round, the superciliary ridge is very slightly marked; there is but a single row of small linear scales between the labial and suborbitar. The ear is of moderate size, the anterior margin having two or three small projecting scales. The scales on the temples are imbricated and smooth ; those of the sides of the neck also imbricated but very small. The neck is almost wholly without a fold, having merely a slight loose elevation of the skin. The scales of the back are small, rhomboidal, flat, the carina low, and not pointed at the extremity. They consist of about ten rows on each side of the median line. Those of the sides and belly are wholly without any notch on the free margin. The scales around the axillro, and those of the posterior face of the thighs are granular. The tail is of considerable length, being more than twice the length of the head and body. The limbs are remarkably long; the anterior, when pressed ngainst the side, rr.aching to the setting on of the thigh, and the posterior reaching forwards nearly to the car. The general colour of the upper parts is greyish brown, with a yellow longitudinal fascia extending on each side from the upper edge of the orbit to some distance along the tail-and another from beneath the eye to the thigh. The middle of the back is lighter than the sides-beneath the second lateral line the colour fades, and on the belly it is pale buff or light yellow. The sides are dotted with black; and there are some dark waved lines and dots beneath the lower jaw. This species is at once distinguished from every other by the fold of the neck being, scarcely cognizable. It is however not so absolutely wanting as in Pr. Chilensis. DIMENSIONS. Length of the head ...................... .. of the body .................... . of the tail ...................... .. Total length .... .. Length of anterior extremity ........... . of posterior extremity ........ . Inches. Lines. 0 1 3 5 0 5 4 8 7 7 1 A single individual of this species was taken by Mr. Darwin at Port Desire. ~ |