Guido Poppe has a couple of nice pictures of the [formerly] "missing shell" on his web site. It certainly does not look immature, nor does it look like a Marginella. To see the images, go to his site at: http://www.club.innet.be/~year0078/ click on gallery click on Cypraeidae scroll down to subfamily CYPRAEOVULINAE under which you'll find Genus Chimaeria, and a couiple of great pictures of Chimaeria incomparabilis Paul M.