32 
Annals of the Tkansvaal Museum. 
forming a suture with, the frontal ; our large series of this species 
shows that the frontonasal is more usually quadrangular and does 
not reach the frontal, so that the prefrontals generally form a suture. 
Sometimes there is no loreal, this scute having fused with the 
preocular. Occasionally, too, there are only five upper labials, and 
not infrequently the frontonasal reaches the rostral. 
A very distinctive character is furnished by the scaling of the 
flanks, these scales being somewhat smaller than the dorsals and 
separated from each other by granular intervals. Also a very constant 
character is the dark or black (in spirit specimens) lateral band which 
is specially marked in the shoulder region. 
However, after examining numerous specimens, I have come to 
the conclusion that the most reliable point of distinction from 
Z. covdylus is to be found in the shape of the head. The differences 
between these two species are as follows : — 
Z. cordylus has the head flattened from above and expanded 
laterally in the temporal region, and the relation of the greatest 
breadth to the length (from tip of snout to hind margin of the 
parietals) in a representative series of specimens is 20-20'7, 20*3-21*2, 
20-21*8, 18-19*3, 21*3-23, 20-22, 19*9-20*5, the figures representing 
actual measurements in millimetres, whereas in Z. jonesii the head 
is not so much flattened, and is only slightly expanded in the 
temporal region, so that the ratio for this species is 15*8-18*4, 
15*7-18*2, 16-18*3, 16*5-19, 15*6-18*8, 15-18*2. > 
Nevertheless this mode of differentiation is not altogether trust- 
worthy when dealing with half-grown specimens of Z. cordylus, as 
the following figures relating to this species show : 14*5-17, 15*1-17*9. 
And, indeed, though it is usually quite easy to distinguish between 
young cordylus and jonesii when the sum total of the characters is 
considered, yet rarely a specimen appears which combines together 
the characters of both species, and identification thereon becomes 
merely a matter of speculation from the locality data. 
Z. cordylus has the head scales smooth or irregularly rugose, 
whereas in jonesii the head scales, including the temporals, are finely 
and reticulately ribbed all over. 
The scales on the dorsal surface of the body are, in jonesii, 
strongly keeled and obliquely ribbed, whereas, in cordylus, these 
scales, at any rate in the mid-dorsal area, are almost or entirely 
smooth and not ribbed. 
The number of transverse rows of dorsal scales (counting from 
the parietal scutes to the base of the tail) varies in jonesii from 
twenty-three to twenty-six, and in cordylus from twenty-seven to 
twenty-nine. In typical specimens of the two species the lateral 
scaling of jonesii, or the transversely elongated frontonasal of 
cordylus, are good points of distinction, but, occasionally, such 
characters are misleading. For instance, a half-grown specimen 
from Selati (Zoutpansberg District), in most respects typically 
jonesii,' has large lateral scales strongly imbricated as in cordylus. 
A specimen from Uitenhage (Albany Mus. coll.) has the characteristic 
shape and general appearance of jonesii, but is aberrant in that the 
lateral scaling is just as in cordylus, the frontonasal is transversely 
elongated and the dorsal scales are in 27 rows. A specimen from 
Steynsburg, C.C. (Albany Museum coll.) agrees almost precisely with 
that from Uitenhage, but differs in that the ribbing of the dorsal 
scales is only very faintly developed. 
