The Macerich Co. said in a filing today with the U.S. Securities and Exchange Commission that it has received a second, higher offer from Simon Property Group Inc. for the 51 regional malls it owns, including Southridge Mall in Des Moines. Simon is an unsolicited suitor for Macerich, which was founded in Central Iowa and is now based in Santa Monica, Calif. The most recent bid is $95.50 per share, or $16.8 billion. On March 9, Simon offered $91 a share, or $16 billion. Macerich turned down the first offer, saying it undervalued the company, and it raised questions about the legality of the deal. Macerich has adopted board governance rules that are designed to protect it from future takeover attempts.