Wikipedia
Microderoceras
Microderoceras is a flat sided, evolute, radially ribbed Lower Jurassic ammonite belonging to the ammonitid family Eoderoceratidae and superfamily Eoderocerataceae. Its whorls are subquadrangular in section; venter on the outer rim, rounded; sides with two rows if distinct spines, tubercles on internal molds, formed at either end of the ribs.
These shelled cephalopods, named by Alpheus Hyatt in 1871, are part of the now extinct Ammonoidea, which are distinct from the shelled nautiloids still found living today.