Dugès (1829) =>
http://vipersgarden.at/PDF_files/PDF-3198.pdf
Fitze’s reasoning =>
http://www.vertebradosibericos.org/rept ... saedw2.pdf – section “History of Nomenclature”
“In the table of his [= Dugès'] original publication (page 339), he erroneously wrote L. Edwarsiana instead of L. Edwardsiana, resulting in some confusion.”
As Dugès repeatedly (thus seemingly consciously) dropped the “d” (see the use of the term “l’Edwarsien” and the species account starting at page 386), Fitze's reasoning hardly seems to justify use of “edwardsianus”.
=> Psammodromus edwarsianus is the correct name (regardless of linguistic considerations)