House ad for Showcase #27 [Sea Devils] (July-August 1960); printed in Batman #133 (August 1960)
Ad designed and lettered by Ira Schnapp
That's actually not the actual art for the actual cover of the actual Showcase #27 which features the actual first appearance of the (actual) Sea Devils, actually. Here it is, a gorgeous color wash cover by Russ Heath (who is actually pretty great in and of himself...actually.)
Cover of Showcase #27 [Sea Devils] (July-August 1960), painted wash art by Russ Heath
The art in the ad above is (actually) repurposed and recolored from the splash page of the story.
Splash page of Showcase #27, script by Robert Kanigher, pencils and inks by Russ Heath, letters by Gaspar Saladino