Green Dot Corp. has commenced a larger-than-expected secondary offering of more than 4.29 million common shares, all held by current stockholders.

Shares of the Monrovia prepaid debit card company to be sold represent about 10 percent of outstanding shares, with an aggregate value of more than $251 million, according to a late Thursday filing with regulators. When first announced last month, the company expected only $100 million worth of stock would be sold. Sellers include board member Virginia Hanna, according to a Wall Street Journal report, but not Wal-Mart Stores Inc., which has a minority stake in the company.

Green Dot said it would receive no proceeds from the offering. The company went public in July in a more than $140 million offering of shares, also sold by officers and other insiders, and has yet to raise money by creating new shares to sell.

J.P. Morgan and Morgan Stanley are joint book-running managers for the offering. The underwriters will have a 30-day option to purchase from the selling stockholders up to an additional 426,904 shares to cover any over-allotments,

Shares were down 73 cents, or 1.2 percent, to $58.98 in midday trading on the New York Stock Exchange.