Help me identify this shell from Sanibel Island

[novice]

Thanks, Dave.  I am really enjoying this site.  From what little I have read, there seems to be some system for "grading" shells.  Is it better to have a specimen of size with some minor defect(s), or a smaller one that is perfect?  I have been collecting only about 4 years and just by chance ended up on Sanibel, where the shelling bug bit me badly.  I have collected some very nice varieties.  So, I'm just curious.  Most of my nicest ones (in my opinion) were collected after storms near Sanibel.