Turtle Shell are one of the GF Learning Items in Final Fantasy 8. Listed below are the effects of the Turtle Shell. Where you can find the Turtle Shell and how to obtain the Turtle Shell.
Turtle Shell - Allows the Guardian Force to learn the Vit+20% ability - The Turtle Shell can be stolen from the Armadodo. It can alse be refined from the Adamantoise Card and the X-ATMO92 Card.
More guides can be seen at the Final Fantasy 8 Forums.The complete list of all GF learning items can be found at FF8 Guardian Force Learning Items Guide. If you have more info about Turtle Shell please post them below.