Yes, pyramidding in turtles = not good. Generally this means that the turtle is either being overfed or doesn't have proper lighting or both. Often causes problems with their internal organs, ultimately leading to premature death.
There are a bunch of variations of map turtles that are pretty damn cool, and their shells do have a kind of jagged appearance. Texas maps are pretty sweet, they have a lot of orange in them. You might also dig a black knobbed map. Google for some pics, there are many species of map to choose from. Also, maps generally stay smaller than most other species of turtles and a 40 gal would be just fine for a couple of them.
Care for most turtles is pretty basic: give them water (with adequate filration/heat), a basking spot with a regular incandescent bulb AND a UVB bulb (imperative!). Pick a good pellet/stick food as a staple (my turtles eat the same pellets I give my fish, which is nice) and give them some different things to eat every now and again to keep their diet somewhat varied.
