This picture is of a Harpoceras subplanatum ammonite fossil at the Museo di Paleontologia at Sapienza University of Rome Italy. Creatures like this existed at the time of the early Jurassic Period (lower Toarcian). The fossil was found Holzmaden, Bavaria, Germany.
UPDATE: Originally called this Harpoceras falcifer but changed it to H. subplanatum
Image taken in June 2014.