The figures below illustrate the microscopic structure of some keeled and smooth scales. The images are magnified 2000-5000x.

Keeled scale (Pinou) Rough Green Snake Opheodrys aestivus	Smooth scale (Pinou) Smooth Green Snake Liochlorophis vernalis AKA Opheodrys vernalis
Keeled scale (Smith, et al.) Northern Water Snake Nerodia sipedon	Smooth scale (Smith, et al.) Pipe Snake / False Coral Snake Anilius scytale

 

References: Thanks to the individuals below for allowing the reproduction of their photomicrographs on this site.

Theodora Pinou. Snake scale microdermatoglyphics.
From: http://pantheon.yale.edu/%7Etp36/research.htm
http://pantheon.yale.edu/~tp36/pinou.htm

Hobart Smith, et al. The function of squamate epidermatoglyphics.
From: http://herpetology.com/1phs30.html
Published in: Bulletin of the Philadelphia Herpetological Society, Vol. 30 (1982) and Vol. 31 (1983-4 photos)