I'm unable to find any concrete evidence revealing the identity of this medallion, but I'm very confident it's concept art. Let's take a look at some other pictures to see why.
Here's a close up of the four medallions from your original photo, which I've taken from the same book; The Legend of Zelda: Art and Artifacts.
In the section for the pixel art of A Link to the Past, we're treated to this image.
As you can see, there's definitely only three medallions used in the game, although I suppose that's why you're asking in the first place. Here's where it gets interesting; from the Zelda Wiki page for the Quake Medallion we find this image.
The wiki states that this is the artwork from the game's instruction manual, and it's certainly a closer representation of the pixelated design. The fact that the Art and Artifacts book doesn't include this design, and that the only designs which match the manual and pixel designs are the top two, leads me to believe that this book isn't a complete compendium of Nintendo's Zelda artwork and only features some of their works (probably allowing them to sell another edition in a few years time).
As such, I strongly believe the bottom two medallions are concept art for the Quake Medallion, or perhaps the Quake Medallion and a fourth medallion which was later scrapped. As Radhil suggests in the comments, it's not too dissimilar from the Light Medallion from Ocarina of Time, and not letting good art go to waste could've been recycled and altered after being dropped from ALTTP, although this is pure speculation.