P r o c t o t r e t u s g r a c i l i s . N . S .
P l a t e I .—F ig . 2.
Corpore gracili : capitis squamis Icevibus, non imbricatis : aurium margine anteriore
minuté bi-tridentato : collo vix plicato, squamis imbricatis: serie unicâ squamaruxt
supralabialium: femorum facie posteriore omninà granulosâ.
Habitat, Port Desire, Patagonia. Mr. Darwin, MS.
D e s c r ip t io n .— T h is new species is more slen d er an d graceful in its g en e ral form th an any o th e r of
th e genus, n o t exc epting P>\ teiiuis, which in its g en e ral proportions it considerably resembles.
T h e h e a d is ra th e r short, the a n te rio r p o rtio n in clu d in g th e eyes being n e a rly an equilateral
triangle. T h e muzzle is rounded. T h e scales o f th e head flat, ra th e r large, consisting beh in d
th e nose o f th re e series o f 2, 3, 3, a n d 2, mostly hexagons. T h e nostrils are small and
perfectly ro u n d , th e superciliary ridge is very slightly marked ; th e re is b u t a single row of
small lin e a r scales b etwe en th e labial an d suborbitar. T h e e a r is o f m odera te size, th e an te rio r
margin hav in g two o r th re e small p ro jec tin g scales. T h e scales on the temples are imbricated
an d smooth ; those o f th e sides o f th e neck also imbricated b u t very small. T h e neck is
almost wholly without a fold, hav in g merely a slight loose elevation o f th e skin. T h e scales o f
the back are small, rhomboidal, flat, th e ca rin a low, a n d n o t p o in ted a t th e extremity. T h e y
consist o f ab o u t te n rows on ea ch side o f th e median line. Those o f th e sides a n d belly are
wholly with o u t a n y notch on th e free margin. T h e scales a ro u n d the axlllæ, an d th o se o f the
posterior face o f th e thighs are g ranula r. T h e tail is o f considerable len g th , bein g more than
twice th e le n g th o f th e h e a d a n d body. T h e limbs are remarkably long ; th e ante rior, when
pre ssed against th e side, re a ch in g to th e settin g on o f th e thigh, an d th e posterior re aching
forwards n ea rly to th e ear. T h e g en e ral colour o f th e u p p e r p a rts is greyish brown, with a
yellow long itu d in a l fascia e x te n d in g on ea ch side from th e u p p e r edge o f th e orbit to some
distance along th e ta il—an d a n o th e r from b en e a th th e eye to th e thigh. T h e middle o f the
back is lig h te r th a n th e sides—b en e a th th e second lateral line th e colour fades, and on the
belly it is pale b u ff o r lig h t j'ellow. T h e sides are d o tted w ith black ; and th ere are some dark
waved lines an d dots b en e a th th e lower jaw.
T h is species is a t once distinguished from eve ry o th e r by th e fold o f the n eck being
scarcely cognizable. I t is however n o t so absolutely wan tin g as in P r . Chilensis.
DIMENSIONS.
Inches. Lines.
Length of the head.................................. 0 5
of the body .............................. I 4
of the tail ................................... 3 8
Totallength 5 7
Length of anterior extremity ............ 0 7
of posterior extremity ............ 1 I
A single individual of this species was taken by Mr. Darwin at Port Desire.
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