The depiction is of a cult statue of the “Genius” or spirit of the Senate on a pedestal, togate and holding a branch and wand. All this is framed by columns and a domed ceiling.
The actual location of the shrine in Rome is not known, although it could have been part of the palatine complex. Nor is the reason for the type being used only in 158-9 known.
The scarce dupondius (RIC 1014) at the top of this note is for sale and can be purchased by following the link to Mauseus on vCoins HERE.