Etology, a Foster City, Calif.-based operator of an online advertising marketplace, has raised $4 million in Series A funding, according to a regulatory filing cited by PE Week. Backers include Mustang Ventures, DG Incubation and CGM Marketing.

Etology lets Web site owners sell their ad space directly to advertisers, serving text ads and banner ads in standard ad units, including banners, skyscrapers and inline ads. It lets Web site owners determine their own pricing.