Ladies Seamaster DeVille

[DRDT]

My wife purchased a ladies Seamaster DeVille watch at a local auction recently. It works well enough but the face could do with a clean. We think the watch is from the '60s. It is an 18mm gold-plated case with a stainles steel back on which is a seahorse with the word SEAMASTER above it and the Omega logo underneath. Under that is the word 'waterproof'. I believe the back is not a screw type but cannot find any crevice in which to insert a small tool to prise it off so that the internal numbers can be checked. Does anybody know when the Seamaster deVille range was made and if there is any other information on this site on the range etc. Thank you.