10 ZOOLOGY. 
Descr. The head is subovoid, being depressed upon its upper surface; the snout is rounded, 
and the eye, subcircular in shape, is of moderate development, its diameter being equal to the 
width of the vertical plate upon the middle of its length. The vertical plate is large and sub- 
pentagonal, either slightly concave upon its sides or linear; its posterior extremity being 
moderately angular. The occipitals are a little shorter than the vertical, but anteriorly nearly 
as broad. The postfrontals are broader than long, extending but little to the sides of the head, 
being posteriorly rounded. The prefrontals are subtriangular, irregularly rounded off, and do 
not reach the nostrils. The rostral is subconical, concave beneath. The nostrils are small 
and subelliptical, situated between two plates the sutures of which are sometimes obliterated 
either above or below these apertures. The loral is quadrangular and larger than either the 
post or prenasals, which have the same general shape. There are two anteorbitals; the upper- 
most is longer than high, and a little longer than the lower one, which is rather narrow and 
elongated ; also two postorbitals nearly equal in size and similar in shape. The temporal 
shields, seven or eight in number, are so small and so much like the scales, that there are only 
two that may readily be distinguished from the latter by their shape. The upper labials are 
seven in number: the fifth being the largest, the sixth is the next in size, then the fourth, the 
third, and the second ; the seventh is a little larger than the first, which is the smallest of all. 
The third and fourth constitute the inferior rim of the orbit ; their suture being situated beneath 
the pupil. The symphyseal is triangular; the lower labials, being nine in number, diminish in 
size both forwards and backwards from the fifth, which is the largest of all ; the seventh, eighth, 
and ninth are rather narrow and elongated, whilst the four anterior are higher than long. 
The first one in particular is nearly twice the height of the second, and separates entirely the 
symphyseal from the anterior mental shields, of which it assumes the general feature. There 
are two pairs of mental shields of about the same length, but the posterior pair is more slender 
and posteriorly subacute. 
The body is subcylindrical, thickest upon its middle, tapering both posteriorly and amteriorly 
where a somewhat contracted neck separates it from the head. The tail is subconical, pointed 
posteriorly, rather short, constituting about the sixth part of the entire length. The scales 
are smooth, disposed upon nineteen longitudinal series; they are subacute posteriorly, and 
largest upon the external series, gradually diminishing hence to the central or dorsal series. 
On the nape and under the head they are the smallest. The abdominal region is rather nar- 
row. There are one hundred and fifty-five abdominal scutelle, the posterior one being bifid, 
and forty-three subcaudal scutelle, all of which bifid. 
Abd. sc. 1541. Sube. sc. 43. Dors. rows 19. Total length 15 inches and ,%; tail 23 inches. 
The ground-color appears now olivaceous brown above, yellowish beneath. The anterior 
margin of the abdominal scutell being jet black with a subtriangular blotch upon their middle 
region, and occasionally also upon their extremities, the lower surface of the body may assume 
quite a maculated appearance. The anterior margin of all the scales is black, but when in 
their normal and imbricated state, the black is not seen externally except upon the fourth and 
eight series on either side, thus constituting two pair of obsolete vittee. The middle dorsal 
series exhibits likewise the black margin of its scales, though in a less conspicuous manner as 
the specimens grow to a larger size. In the very immature condition almost every scale shows 
its black edge, constituting irregular zigzag lines. The dorsal vittze sometimes assume the ap- 
pearance of a series of double crescents contiguous upon their convexity: this is owing to the 
fact of the black extending along the sides of the scales. The lateral vitte, from the neck 
ascend to the occipital region of the head, the sides of which are marked by two narrow black 
stripes, the upper one slightly arched, extending from the posterior rim of the orbit to the angle 
of the mouth ; the other runs obliquely from the lower rim of the orbit, across the fourth and 
fiifth labials to the edge of the mouth. 
This species was collected in the vicinity of Santiago, Chile. 
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