I am the BEST at identification!
This picture link below is of a MALE snail. Female coloration is more drab. Which is what you have in your pictures.
http://www.firama.com/seashells1/1746/index.asp
Nassarius Pfeifferi
Shell ID: 1746
ItemType: Seashell
Family: Nassariidae
Genus: Nassarius...
It's been awhile. To be honest my tank was doing very poorly. But since it has recovered. I have a green BTA and a true percula now. The perc actually hosted in the BTA in three days. I was shocked. Anyhow, here are the pics: