Sinistral Turbinella pyrum

The Harvard Museum of Natural History currently has an exhibit entitled Mollusks: Shelled Masters of the Marine Realm, showcasing 300 of the museum's ten million specimens.

A display case devoted to snails contains two shells of the same species of Indian sacred chank (Turbinella pyrum). One is coiled with an opening to the right, the usual thing; the other has its opening to the left. There are only three known examples of such a left-facing shell in the United States... A local amateur shell collector has observed that the shell is so valuable in the marketplace that armed guards should be positioned on either side of the case 24/7.

I found the photo of dextral and sinistral Turbinella at Reverse Coiled Gastropods:

A vast majority of the tens of thousands of marine and non-marine gastropod species are normally dextral (right handed - i. e., the shell opening is to the right when held spire upwards) while only a limited number of taxa such as Busycon sinistrum, the few species of the Fasciolariid subgenus Sinistralia and most of the speciose family Triphoridae, among others, are normally sinistral (left handed - the shell opening is to the left when held spire upwards). However, accidents of nature do happen, and occasionally a sinistral specimen of a normally dextral species or a dextral specimen of a normally sinistral species will be found - albeit rarely.

 In some 40 years of specializing in "reverse coiled" or "abnormally sinistral or dextral" gastropods, Jacksonville amateur malacologist Harry G. Lee has assembled a collection of 164 individual species which had coiled in a direction contrary to the norm. This collection includes 102 Recent, three fossil marine and 59 non-marine species.