The common skate, Dipturus batis. This, obviously, is the not-up side, referred to by zoologists as "ventral" (the opposite of "dorsal"). Botanists would call it "abaxial". Image by Misjel Decleer, published under a Creative Commons Attribution Non-Commercial Share-Alike 3.0 license. Click image for link.

Just in case you thought taxonomy was a strictly useless pursuit . . .

. . . and you can see how skates fit into the rest of the cartilaginous fish (fish with cartilage skeletons like sharks) here.