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James River Group Holdings Ltd., the insurer backed by D.E. Shaw & Co. and Goldman Sachs Group Inc., is seeking a valuation of as much as $685 million in an initial public offering.

Investors are offering 11 million shares for $22 to $24 apiece, the insurer said in a regulatory filing Tuesday. The company will have 28.5 million shares outstanding after the planned sale, with Shaw cutting its stake to as low as 50.4 percent from 72.6 percent.

D.E. Shaw, a hedge fund company founded by billionaire David Shaw, bought James River for more than $560 million in 2007. The shareholders are seeking to benefit from increased investor interest in Bermuda-based insurers that cover specialized risks for commercial clients. Ironshore Inc., the insurer led by former American International Group Inc. executives, struck a deal in August to sell a 20 percent stake to Fosun International Ltd. for about $463.8 million.

“By focusing on specialty markets in which our underwriters have particular expertise and in which we have fewer competitors than in standard markets, we have greater flexibility,” James River said in the filing. The company focuses on “niches where, because of our expertise, we can distinguish ourselves in the underwriting and pricing process.”

Shaw and New York-based Goldman Sachs each are offering as many as 6.33 million shares, a sum that includes an over- allotment option. A sale of that size would cut the investment bank’s stake to 4.1 percent from 26 percent. The insurer said it plans to pay quarterly dividends on common stock after the offering, beginning the first three months of 2015.

Stifel Financial Corp.’s Keefe, Bruyette & Woods Inc., UBS Group AG, FBR Inc. and Bank of Montreal will manage the share offering, according to the filing.

–With assistance from Laura Davison and Noah Buhayar in New York.