Niolamia is a fascinating turtle. Living during the Eocene (probably), it is one of the earliest known meiolaniids. What makes meiolaniids special is not just that they were sizable land turtles, but two other things 1) The massive horn-like scales, primarily those marked A-C. Niolamia has some of the most impressive ones at that, with the A scale forming an almost ceratopsian-like frill at the back of the head and two large, flattened, side-ways directed horns before said frill. 2) The long tail was armored, covered in bony rings with spikes and in some species even a straight up tail club
The two images above are things I put together for the Wikipedia page of Niolamia. The first shows the growth of the species. The small skull is a juvenile Niolamia, originally described as Crossochelys but synonymized by later researchers. The bigger skull (to scale) is the neotype (or holotype?) of Niolamia. Check out an older post for some history on that. The other is a simple sideview of the skull and lower jaw, nothing too fancy.
The bottom two photos aren't mine but those of Victoria Arbour, but show the weirdness and size nicely. The first image shows Niolamia (right) next to Ninjemys (left). While the second picture shows Ninjemys with as I said Victoria Arbour. Which still gives a good idea of how big these animals heads were.