OK, let me confuse things even more. I have a 1956 Italian catalog from Beretta. They show several variations for the 409. There is the 409, 409 L, 409 PB and the 409 BIS. The picture of the 409 BIS has that same rib. It specifically states that the right trigger is articulated. It also talks about a triple lock up. But they had that on many of their guns.
I can not find the 408 in any of my catalogs or references, though I have no doubt that the model existed. The problem with Beretta is that they often marketed the same gun in different countries and changed the designation from country to country. I do see 408's show up on Italian auction sites. It also has that same rib. Go figure.
A 409 BIS
http://si.armiusate.it/catalogo/233/Fuci...2-2-2-STEL.html
A 408
http://www.armerialabeccaccia.it/dett_art.php?id=256
Pete
