The Half-Maiorina denomination
A billon coin replacing the heavily reduced centenionalis introduced by Constantius II and Constans in AD 348.

The half maiorina weighed 2,6 grams initially, but like its big brother the maiorina it was quickly heavily reduced.
Half-Maiorina

(1) Constans 348/349 AD
Obverse: DN CONSTANS PF AVG
Reverse: FEL TEMP REPARATIO, phoenix radiate standing right on pyre
Ref: Sear 18717