When the eggs hatch and the little whelks want to escape they go through the little holes you see above in the detail photo. If a hole isn't present in the casing then the whelks didn't hatch.
We also found a nice selection of seashells on the beach. One of my favorite of the weekend was this large Pen Shell. I especially liked the barnacles that had adhered to the surface. Barnacles always remind me of teaching dock class at Jekyll. I must have taught hundreds and hundreds of children about barnacles. They reall are quite fascinating and if you don't know much about them then you should do a little reading.