These come from one of many accounts selling high end counterfeit world coins on the US ebay. They didn't dare list these on US ebay though. Edit: stealing sellers photos for longevity. http://www.ebay.com/itm/1826-Silver-50c-CAPPED-BUST-HALF-/251962772999?pt=LH_DefaultDomain_77&hash=item3aaa26ce07&nma=true&si=a65iHIzYdkZxp4NuTGARRhh%2FHy8%3D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557 http://www.ebay.com/itm/1833-Silver-50c-CAPPED-BUST-HALF-/251962760739?pt=LH_DefaultDomain_77&hash=item3aaa269e23&nma=true&si=a65iHIzYdkZxp4NuTGARRhh%2FHy8%3D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557
Those do appear to be counterfeit. They look a little bit like some vintage counterfeits, but I don't have a Dauvignon catalog to match them up to. They are probably much more recent.
Ok, so, what gives these away as fakes? The photos don't show any luster, and the surfaces look lifeless and weird. The 1833 seems to have a couple of casting bubbles near the obverse stars at around 8:00. I can't see anything wrong with the details, but I don't really know my way around Bust halves. :/
The 26 I would agree with dcarr as being a vintage counterfeit. That was before they figured out rims. The second looks newer.
They are both new. I can't give you any good reason as I have not seen them in hand, but the source is well known for distributing tons of newly made counterfeits of world coins. They have not gone into US coins until recently it seems. And they also do not match any of the Davignon pieces.
From what I have seen, they are struck rather than cast. The details are always right, but the overall "look" isn't.