Rasenia is an extinct ammonoid cephalopod genus belonging to the superfamily Perisphinctoidea. These fast-moving nektonic carnivores lived during the Upper Jurassic period, in the Kimmeridgian and Tithonian ages.
This genus gets its name from Market Rasen in Lincolnshire (Midland England), place where it is frequently found.
Fossils of species within this genus have been found in the Jurassic sediments of Russia, France and United Kingdom.