Watch List notes:

Anonymous. ca. 91 B.C. AE quadrans (15.8 mm, 2.86 g, 6 h). Rome mint. P·NERVA, head of young Hercules right, wearing lion's skin headdress; three pellets behind / ROMA, prow of galley right; horse standing above, three pellets to right. Crawford 292/4a; Sydenham 549b. VF. 

Ex RBW collection (not in previous sales). 

Crawford calls the animal on the reverse a horse, but several specimens have horns and an up-turned tail. A goat and antelope have been recommended as other possibilities.