Got this one in an uncleaned lot a couple weeks ago. Just arrived today from Germany.
Procopius, Usurper against Valentinian I
November 365 - May 366
AE3
DN PROCOPIVS PF AVG
REPARATIO FEL TEMP
Emperor standing, holding standard and resting hand on shield
Mintmark CONSA, Constantinopolis
Rare

Procopius was Julian II's maternal first cousin, making him the very last member of the Constantinian dynasty. He acted as an envoy to the Sassanid empire for Julian, and was later entrusted with several thousand troops in Julian's fateful campaign. It is said that Julian nominated Procopius as his heir after his mortal injury, but at any rate, Procopius surrendered all power to Jovian in 363 and sought a quiet retirement.
This did not last long, as Jovian met his untimely demise and was succeeded by Valentinian, who ordered the arrest of Procopius, as the last possible claimant to the purple as the final living member of the previous dynasty. Procopius was tipped off and fled to Constantinople. Knowing that he was probably dead either way, he declared himself emperor and attempted to rally support in the eastern capital. He was able to amass an army, but was no match for Valens, who was sent to deal with him. He attempted to flee the battlefield, but was turned in by his troops and later executed.