What is "stereosaurus"

"Stereosaurus" (meaning "solid lizard") is the name given to an as-yet undescribed genus of plesiosaur. Among the species are: "Stereosaurus platyomus", "S. cratynotus" and "S. stenomus", all coined by British paleontologist Harry Seeley, who considered them to be plesiosaurian, in 1869. None have ever been formally described, and since so much time has passed, the original remains may have been lost or renamed something else by now.