4 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



Proctotretus gracilis. N.S. 



Plate I.— Fig. 2. 



Corpore gracili : capitis squamis Icevihus, non imbricatis : aurium margine anteriore 

 nmiuth hi-tridentato : collo vix plicato, squamis imbricatis: sei'ie unicd squamarun 

 supralabialium : femorum facie posteriore omninb 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 axillae, and those of the 

 posterior face of the thighs arc 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 head 5 



of the body 1 4 



of the tail 3 8 



Totallength 5 7 



Length of anterior extremity 7 



of posterior extremity 1 1 



A single individual of this species was taken by Mr. Darwin at Port Desire. 



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