Odd one Out

See if you can spot the odd one out of the group of shells above, which are all the same species. If you need help, see yesterdays blip. I reckon that it will get figured out fairly quickly, but if it doesn't I will give the answer tonight.
This species is called Marginella (Bullata) bullata. It is a member of a small group of Marginellas which are endemic to Brasil. At 5 to 10 cm in length it is also one of the largest - most of my shell work on these marine molluscs involves the use of a microscope. The family has naturally glossy, often very colourful and patterned shells, and when they reach maturity produce a thickened margin or lip (hence the name). The genus Bullata have large shells and the spire is low or often completely buried, as in the cowries. This particular species is often found dead on the sand outside octopus holes - they must be a tasty treat!