What is "megalytoceratinae"

Megalytoceratinae is a subfamily of lytoceratids ammonites consisting of planulate forms, i.e. those with moderately evolute compressed shells with bluntly rounded venters, in which the outer whorls become smooth and sutures tend to resemble those of the Perisphinctidae. The family includes two genera, Megalytoceras, and Metrolytoceras, from the Middle Bajocian of England and a third possible member, Asapholytoceras, from the Toacian of southeastern Europe.