Ad lapidem statements are fallacious because they fail to address the merits of the claim in dispute. Ad hominem arguments, which dispute the merits of a claim's advocate rather than the merits of the claim itself, are fallacious for the same reason. The same applies to proof by assertion, where an unproved or disproved claim is asserted as true on no ground other than that of its truth having been asserted.
Carl replies, "That can't be true. Bob is not an embezzler, not now or ever. He simply wouldn't do such a thing. It's nonsense, a ridiculous claim on its face."
Because it denies Albert's claim, but gives no reasoning or evidence proving it untrue, Carl's reply is an argumentum ad lapidem in form. In making it, Carl has commits the ad lapidem fallacy, and we would be reasonable to discount it.