You are correct Pete, technically rays are a cartilaginous fish related to sharks , cartilaginous fish are jawed fish and skeletons made of cartilage rather than bone. The skeleton is cartilaginous. The notochord--A flexible rod-like structure that forms the supporting axis of the body in the lowest chordates and lowest vertebrates and in embryos of higher vertebrates, which is present in the young, is gradually replaced by cartilage. The class Chondrichthyes ( Cartilaginous fish) also lack ribs, so if they left the water, the larger species's own body weight would crush their internal organs long before they would suffocate.
So my bad on not clarifying the no ribs aspect. But they do have a structure resembling ribs, but is not bone nor does it have marrow. The gills are still located inside the gill slits on the underside of ray