Fifteen star Secession Flag in use in Texas during February and March of 1861.  This version is a variation of the flag of the Republic of Texas.
Frank Wilson Kiel, "A Fifteen-Star Texas Flag: A Banner Used at the Time of Secession: February 1861 and March 1861," The Southwestern Historical Quarterly 103, no. 3 (January 2000): 356-365.
Glasshouse