Zynga, the social-network game developers behind Facebook time wasters like Farmville, YoVille, and Mafia Wars, have added some new games to their…er…stable.

Specifically, they scooped up Newtoy Inc., they of the “Games With Friends” franchise (Words With Friends, Chess With Friends, etc.).  Rebranded as “The Zynga With Friends Studio,” Newtoy’s David Bettner becomes the studio director, while brother Paul is now a Zynga vice president and general manager of Zynga With Friends.

Terms of the merger were not disclosed.  Also not disclosed: any additional falloff in productivity by workplace Facebookers.