306 
THE EEPTILES OF EGYPT. 
The ventrals vary in Eastern Africa from 155-198 = 43 : in Western Africa (Senegal 
to Angola) from 157-181=24. The range of variation in the subcaudals in Eastern 
Africa is 90-116 = 26, and in Western Africa is 97-116 = 19. 
It will be observed from the foregoing table that it is almost invariably the case for 
the fourth and fifth labials to enter the orbital margin in this species, but that 
occasionally exceptions occur, and that in these instances it is the fifth and sixth 
Eig. 12. 
A 
Type of Coluber sibilans, Linn. (Upsala Museum.) 
labials that take the place of the former, accompanied by nine labials, as in 
P. schokari. 
The two species P. schokari and P. sibilans are closely allied, but at the same time 
are distinguished from each other by certain generally persistent characters. Thus the 
rostral of the first is broader than high, and that of the second usually higher than broad. 
P. schokari has nine upper labials ; P. sibilans eight. In the former, the fifth and 
sixth upper labials enter the orbit, in the latter the fourth and fifth. As a rule, the 
prfeocular in P. schokari is broadly in contact with the frontal, while in the second these 
shields are generally not in contact, or if they do touch, they do so only to a very 
slight extent. 
