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ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 
Proctotretus gracilis. N.S. 
Plate I. — Fig. 2. 
Corpore gracili : capitis squamis IcBvibiis, non imbricatis : aurium margine anteriore 
minuth bi-tridentato : collo vix plicato, squamis imbricatis: serie unicd scpiamarun 
supralabialium : femorum facie posteriore omnind 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 
pei’fectly 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 axillae, 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 against the side, reaching to the setting on of the thigh, and the posterior reaching 
forwards nearly to the ear. 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. 
Inches. Lines. 
Length of the liead 0 5 
of the body 1 4 
of the tail 3 8 
Total length 5 7 
Length of anterior extremity 0 7 
of posterior extremity I I 
A single individual of this species was taken by Mr. Darwin at Port Desire. 
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