Hello Moshe, Harpa amouretta and H. amouretta crassa can be difficult to distinguish in a photograph, because their general shape, color and markings are similer. But when you hold them in your hand they are easy to separate. H. amouretta crassa is a very thick, heavy, solid form, while the typical H. amouretta is rather thin and lightweight. I think that H. amouretta crassa also has a smaller length-to-width ratio, due to the increased thickness of the body wall, and a smaller aperture relative to the shell size, for the same reason. Paul M.