Following reports in February that Zynga was raising a new round of funding of up to $500 million at a $10 billion valuation, a new filing has emerged showing what appears to be a sale of $490 million in Series C Preferred shares, that had been slated to take place in early March.

The filing, discovered by financial analysis firm VC Experts, could indicate a post-money valuation of $9.1 billion, so within the range of the reports — that’s assuming the full amount of new funding is in, and that all of the authorized shares have been issued.

All Things D, which reported that Zynga was raising up to $500 million in February, named institutional investors including Morgan Stanley, T. Rowe Price, Fidelity Investments, as well as venture firm Kleiner Perkins as participants. The New York Times reported in April that T. Rowe Price is now holding $71.8 million worth of Zynga stock.

One caveat: Zynga’s legal paperwork has taken a tortuous path over the last several years, and it’s not entirely clear what this document is showing. As of today, the company’s stock table includes: Series A Common, Series A Preferred, Series A-1 Preferred, Series B Common, Series B Preferred, Series B-1 Preferred, Series B-2 Preferred, Series C Preferred, and Series Z (which is oddly priced at a penny per share), according to filings.

Zynga’s filings have also come at odd times, oftentimes not corresponding to the dates and amounts of publicly announced fundings. To add to the complexity, there’s been other buying and selling of Zynga stock that has not been officially confirmed. Early investor Union Square Ventures has sold at least a large portion of its stake in the company, according to an industry source, while Google has also reportedly bought a large amount of Zynga stock (which the companies have never confirmed).

We’ve asked Zynga for comment and we’ll update with any further information.

Zynga April 2011