They look remarkable different to rhombeatus, although they do look superficially similar.
My apologies, Bill Branch has just advised me that this specimen is not
Causus bilineatus but
C. rhombeatus Common Night adder. The ventral scale count of 138 also fits
C. rhombeatus but there are still problems with Night adders in Angola and more samples would be useful.
I agree that this specimen does look very similar to
C. rhombeatus from RSA but not quite the same either.
An inaccurate naturalist is a pest and a danger, forever perpetuating illogical deductions and landing later naturalists in trouble. Damm and blast them all to hell in the most painful way. C.J.P. Ionides