Clear rhinestone pot metal clamshell dress clips.  Marked WMCA (White Metal Casters Association) and manufactured during the 1930s.  Some stones have darkened - overall condition is very good for its age. They measure 1" x 1".
 
See "Collecting Rhinestone & Colored Jewelry - 3rd Edition" by Maryanne Dolan for wonderful examples of dress clips. This book also includes a comprehensive section on Designers Marks.