These are the Original Model Force Fins.  According to the Force Fins company, the fins are 

made for kicking equally well for a variety water sport activities: Snorkeling, SCUBA, belly boating, swimming and body surfing subject only to changes in size. Features include Force Fin’s open-toe foot pocket, with your toes free to wiggle about the way they are meant to be. Eliminates cramping by powering the fin blade from your strongest swim kicking muscles.