What Are These?

I have spent many hours searching the internet trying to find out what these unusual shaped mother of pearl items would be used for…with no luck.  I thought perhaps they were some sort of collar stay but I can find no evidence of that.  They measure just under an inch by approximately 3/4 of an inch.  Two of the five are similar, they other three are different.  Two lay perfectly flat and three have a slight arch.

Does anyone know what they are?  What would they be used for?