Before I looked at all of the replies, I thought "Gallienus". Given the relative frequency of Gallienus coins to HE coins, it is even more likely to be Gallienus.
The hairstyle on the forehead of your portrait is clearly that of Gallienus, as is the nose. Also the rugged shape, metal composition, and general condition of your coin are typical for later Ants of Gallienus, while those of Herennius tend to be round and detailed with a high silver content. Here is mine: