What is "psiloceras"

Psiloceras is an extinct genus of cephalopod belonging to the ammonite subclass. Psiloceras fossils are commonly found at Watchet, Somerset, England. Here smooth-shelled Psiloceras planorbis (along with other species) are to be found as usually flattened fossils in the Blue Lias. Unlike most earlier ammonites, which had complex shell shapes and ornamentation, Psiloceras had a smooth shell.