a) young; b) male, common livraea; c) female;  d) male, lower wiew.

From the book "Guida dei Rettili e degli Anfibi d'Europa", by E. N. Arnold and J. A. Burton, ed. Franco Muzzio & c. Original title: "Reptiles and Amphibians of Britain and Europe" (modified).

Original drawing by D. W. Owen.