Based on the New Italy Hoard (Hersh NC 1977), Mattingly holds that the denomination the Dodrans (3/4s of an as = 9 unciae) was first introduced by C. Cassius, not M. Metellus (2004: 220). This rules out his original theory echoed by Crawford in RRC that the type was introduced by the later to provide a space to commemorate a divine ancestor via the legendary Caeculus. Why would Cassius create a new denomination for Vulcan? Mattingly gives a terse answer: “The Vulcanal near the forum was the center of popular and tribunican activity in the early republic.” No footnote. It’s a hard assertion for which to find much support.
Does it have anything to do with Liber on his other new denomination the bes (2/3s of an as = 8 unciae)? What do Vulcan and Liber have in common? Not much but we do have his intriguing passage:
That the two gods could be linked is shown in this little passage from Hyginus’ Astronomica:
According to Eratosthenes, another story is told about the Asses. After Jupiter had declared war on the Giants, he summoned all the gods to combat them, and Father Liber, Vulcan, the Satyrs, and the Sileni came riding on asses. Since they were not far from the enemy, the asses were terrified, and individually let out a braying such as the Giants had never heard. At the noise the enemy took hastily to flight, and thus were defeated.
This text however seems to me another explanation of a common artistic motif “Hephaestus’ return to Olympus”:
The narrative might go back to a lacuna in the Homeric hymn of Dionysus, some speculate. The narrative is mostly deduced from various vase paintings with the help of this passage in Pausanias:
There are paintings here–Dionysus bringing Hephaestus up to heaven. One of the Greek legends is that Hephaestus, when he was born, was thrown down by Hera. In revenge he sent as a gift a golden chair with invisible fetters. When Hera sat down she was held fast, and Hephaestus refused to listen to any other of the gods save Dionysus–in him he reposed the fullest trust–and after making him drunk Dionysus brought him to heaven.