Will of "Samuel Smith, 3d, of Wellfleet", dated 5 Jan 1779, names "Joshua Mayo Smith, son of my late Bro. Zoheth Smith".
[Note: this source, and others, were apparently confused about which Samuel Smith wrote this will, and hence, Joshua Mayo Smith, is often given to his grandfather, rather than his father. Besides carefully identifying the other persons mentioned in this will, consideration of Susanna Knowles' father's name may help.]