I found these fossils(?) this week at Windy Hill, North Myrtle Beach, SC. Each one seems to be half of a cylinder divided vertically. They all contain shelf or ledge spaces shaped like a crescent laying on its side.. The back sides and tops look like (thick) layers on top of layers of build up material. My photos are never good so I added an illustration that I hope will help id them. I have tried to image what the negative areas would be if they were positive. There is no doubt in my mind that they are all three the same things, only what same things are they?