ERSKINE, James 6th Earl of Buchan, jure uxoris

  General Notes:

"In 1617 the earldom came to James Erskine (died 1640), a son of John Erskine, 2nd or 7th Earl of Mar, whose wife Mary had inherited it from her father, James Douglas (died 1601); and from that time the Erskines have retained the title."

from Wikipedia

James married Mary DOUGLAS Countess of Buchan, suo jure, daughter of James DOUGLAS 5th Earl of Buchan and Anne OGILVY, on 18 June 1615. (Mary DOUGLAS Countess of Buchan, suo jure was born about 1601.)