This excerpt taken from the C 8-K filed Jan 15, 2008.
Optional Conversion. As described above under Description of Convertible Preferred StockConversion RightsOptional Conversion Right, and Description of Convertible Preferred StockConversion Upon Certain Acquisitions, the Convertible Preferred Stock may be converted, in whole or in part, into shares of Citigroup common stock at the option of the holders of the Convertible Preferred Stock. The depositary shares may, at the option of holders thereof, be converted into shares of Citigroup common stock upon the same terms and conditions as the Convertible Preferred Stock, except that depositary shares may be converted only in lots of 1,000 depositary shares or integral multiples thereof.
To effect such an optional conversion, a holder of depositary shares must deliver depositary receipts evidencing the depositary shares to be converted, together with a written notice of conversion and a proper assignment of the depositary receipts to Citigroup, to any transfer agent for the depositary shares, or in blank, and, if applicable, payment of an amount equal to the dividend payable on such depositary shares, to the depositary or its agent. Each optional conversion of depositary shares will be deemed to have been effected immediately prior to the close of business on the date on which the foregoing requirements shall have been satisfied, and the conversion will be at the conversion rate in effect at such time and on such date.