Imitations of Roman Republic coinage, Italy, Æ Semis(5.96g, 21mm). 1st century B.C., Italian mint. Laureate head of Saturn right, S behind/Prow of galley right; above, S; to right, dolphin below, ROMA. Cf. Crawford, “Unoffical imitations and small change under the Roman Republic,” AIIN 29(1982), 66; cf. BMC RR(1910 ed) vol II, p. 588, 7 = BM 1906,1103.2817(same obverse die)
Ex Stevex6 Collection, ex CNG e-auction 295, 1/30/2013, lot 368
The last half of the second Century B.C. saw the Roman Republic issuing limited amounts of bronze and while there were a few large issues during the first two decades of the first century, bronze coinage stopped altogether with an issue of Sulla in 82 B.C. and did not resume until the 40s B.C. with issues minted under Caesar and Pompey. While the government and wealthier individuals of Roman society could function on denarii alone, bronze small change was an important part of the day-to-day transactions of regular people throughout Italy and so to fill this century long gap of limited issues of bronze, many types of bronzes were minted across Italy, some of which imitated Roman prow bronzes that were in common circulation and many of which copied symbols from existing bronze series such as the dolphin on this coin. There's no evidence that Rome had laws against counterfeiting or private minting of bronze like they had for gold and silver, so while it's impossible to tell whether or not these coins were officially sanctioned in any way, they were almost certainly tolerated and in truth the Roman government was probably happy that someone was picking up the slack as it left even less pressure on them to mint bronze, which was expensive and served very little purpose for the government itself which generally would have made its transactions entirely in precious metal coinage.
As far as this type in particular, while it copies the basic types of the Roman semis, it isn't exactly imitating a specific Roman type as there are no known official semisses with a dolphin to right of prow: the Crawford 80 series contains other denominations with a dolphin to the right of the prow, and the Crawford 160 series contains a semis with a dolphin above the prow, but neither contains a semis similar to this one. Most likely, this was just a combination of combining an existing set of devices with an existing symbol. Because of the existing coins with a dolphin symbol, this type is actually commonly mistaken for an official Roman coin and the first edition of BMC RR listed this type as an official Roman type in the appendix at the end of Volume II and this coin is actually an obverse die match to the BM coin. It's easy to see why one might think that, but when comparing with official Roman bronzes it quickly becomes apparent that the style is divergent from official coins struck at a similar weight standard and in more recent editions of BMC RR, the BM has updated their attribution and cataloged their coin as an imitation as well.