Cover Fossil

Cover Fossil is a fossil in Pokémon Black and White that can be resurrected to Tirtouga.

https://vignette.wikia.nocookie.net/pokemon/images/a/a4/Cover_Fossil.png/revision/latest?cb=20160124170326

It looks like a shell of a tortoise. The player can get the Cover Fossil, or the Plume Fossil, at Relic Castle. A female Backpacker will have them, and says that she can't hold them all, giving you one generously.