SF-based PlayFirst, a publisher of casual games, has raised a $16.5 million third round led by DCM, with participation from previous backers Mayfield Fund, Trinity Ventures and Rustic Canyon Partners. This brings its total raise to $26.5 million, including the $10 million raised over two previous rounds starting in 2004. The maker of such titles as Chocolatier, Diner Dash and Wedding Dash says it will use the funding to accelerate product development. Along with the funding, the company announced a partnership with RockYou, the maker of social net widgets, to distribute Wedding Dash via Facebook. PlayFirst is betting on the idea that the social networking environment will be a key distribution platform for casual games. In October, MySpace signed a deal with Oberon Media to establish a casual gaming channel and allow its games to be embedded on user pages.