Unknown mollusk egg cases found on St. Pete Beach, FL

I found these washed up on the beach after Tropical Storm Andrea June 7th. I know they are not Whelk or True Tulip egg cases. Does anyone know what they might be?

At first glance, and with no reference material available, I'd say a species of Murex. Where are you?

St. Pete Beach on the west coast of Florida near St. Petersburg.