The Atheris Burtoni viper shown here has either gone extinct or now goes by another name. He appeared in the 11th edition of that famous encyclopedia from 1911. The only references I am finding to the name Atheris Burtoni is others who have shared it from the same source.
The only piece of information we have about this viper is that they (or at least the one depicted) grow to about 12 inches long. We can also infer from the drawing that they hung out in trees.
The viper drawing has two signatures. One of those signatures is Pierre Jacques Smit (1863-1960). I’m not sure what the other signature says. Reverand Pierre Jacques Smit was an English natural history illustrator. He is perhaps most well-known for contributing illustrations to the Catalogue of Birds in the British Museum. While much of Smit’s work remains under copyright, this Atheris Burtoni viper drawing is not.
This image is copyright free and in the public domain anywhere that extends copyrights 70 years after death or at least 120 years after publication when the original illustrator is unknown.