The LOrdship of Napier of Merchiston now passes through female lines, which is how it got into the Scott of Thirlestane family.
Archibald, 3rd Lord Napier of Merchistoun, d. shortly before 7 Aug 1683; in 1676 he resigned his peerage and in 1677 received a new grant thereof, with remainder to heirs male of his body, then to his eldest sister and her heirs male, then to the eldest heir female of her body, then to his other sisters in like manner, then to heirs male, and then to heirs and assigns; on his death the Baronetcy (Napier of Merchiston, cr 1627) became dormant until claimed in 1817.
Sir William Scott, of Thirlestane, 2nd Bt., married Elizabeth, dau of John Brisbane by Margaret, suo jure 5th Baroness Napier of Merchistoun, and passed the Napier Barony to the Scotts, who then took the surname Napier. The Baronetcy held by the present Lord Napier is the Scott Baronetcy on 1666, which seems to pass to heirs male only.
The original Napier Baronetcy stayed in the Napier family.