Bermuda-based insurer Arch Capital Group Ltd. on Friday announced that its founding shareholders will sell more than 2.8 million shares as part of a secondary offering by the company.

A total of 7,285,000 will be sold, with 4,425,000 common shares are to be offered by the company and up to an additional 2,860,000 common shares are to be offered by the selling shareholders.

The announcement came on the same day that White Mountains Insurance Group announced it had sold part of its stake in Bermuda reinsurer Montpelier Re and Endurance Speciality announced the underwriters if its secondary offering planned to exercise their right to buy more shares.

Arch said in its statement: ?These numbers do not include the 1,092,750 common shares subject to the underwriters? over-allotment option, which will be made available to the underwriters by the Company and the selling shareholders pro rata.?

Arch said it expects to use the net proceeds from its sale of common shares for general corporate purposes, including contributions to the capital of its wholly owned insurance and reinsurance subsidiaries to support their underwriting activities.

The company will not receive any of the net proceeds from the sale of the common shares by the selling shareholders.

The offering will be led by Merrill Lynch & Co. and Credit Suisse First Boston as joint book-running managers. Goldman, Sachs & Co., Banc of America Securities LLC, JPMorgan and Fox-Pitt, Kelton will be co-managers for the offering.

Arch closed down six cents at $42.15 on Friday. At that price, the share offering would raise more than $300 million.

Endurance said on Friday that the underwriters of its secondary offering have exercised their option to purchase an additional 944,500 ordinary shares at a price of $34.85 per share to cover over-allotments. This brings the total number of shares sold in Endurance?s secondary offering to 9,794,500.

All the ordinary shares being sold are being sold by certain founding shareholders of Endurance. Endurance will not receive any proceeds from this offering.

Endurance shares closed up 12 cents at $34.32 on Friday.