Who made these pearls and what type of pearl are they called?

by Renee Gagliardo
(Alpine, California)

These pearls were purchased in Japan in the 40's. This is the only information I have. Was told they were Mikimoto pearls, but the marking on the clasp doesn't have the "M" in clam mark, but rather just Japanese writing. I'm assuming they're signed? Can you tell me who made these and what they're called?