The Chondrichthyes are the cartilaginous fishes including the sharks, rays, skates and chimaeras. The Osteichthyes are the bony fish. Both of these groups became established during the Devonian Period about 400 million years ago. The Chondrichthyes differ from the Osteichthyes in many respects, including their <span>skeletons, scales, teeth, buoyancy, swimming, gills and reproduction.</span>
Groundwater, which is in aquifers below the surface of the Earth, is one of the Nation's most important natural resources. Groundwater is the source of about 33% of the water that county and city water departments supply to households and businesses (public supply).
