Both the way that Eros is bending over the lion’s paw and the position of his hands on the superb coin from Serdica—one supporting the paw, the other poised above it—strongly suggest that this is an echo of the old Greek story of “Androcles and the Lion” (quoted by the Antonine author Aulus Gellius in his Noctes atticae, V, 14), in which a runaway slave extracts a painful thorn from a lion’s paw and is later spared by the lion when the two meet again in the amphitheatre.
* This motif also appears on magical gems and amulets, like the following lead amulet (illustration, photos courtesy of Gert Boersema). The obverse shows the Gnostic personification Abraxas (or Abrasax), with a cock’s head and serpent tails and holding a sword (or whip) and a shield; the reverse, on which there is some unclear lettering (AΛKC?), shows Eros/Cupid kneeling to extract a thorn from a lion’s paw, in front of a cave or grove of trees, while above a hare leaps into the sky pursued by a dog (a representation of the soul leaving the body?). Like the coin of Serdica illustrated above, the amulet has been holed to allow it to be worn on a chain or necklace or fixed to a wooden coffin or door lintel.
I am also grateful to Gert for drawing my attention to an essay by Campbell Bonner, “Eros and the Wounded Lion” in the American Journal of Archaeology, Vol. 49, No. 4 (Oct. - Dec., 1945), pp. 441-444, which analyses a group of gems showing Eros apparently bandaging a lion’s forepaw. Noting the presence of solar imagery (not found on the coins), Bonner sees a possible Egyptian connection: in ancient Egypt, the lion was often associated with the sun, and Harpocrates sometimes assimilated to Eros.
References: Jurukova 199; Varbanov 2435-36
References: Hristova/Jekov 22.214.171.124; Varbanov 2079