Smith and Anderson, on Thomas Riggs of Gloucester and Hawkshead, The American Genealogist 82 (2007)

Known from quotations online and from the authors’ final version posted at the link. Cites the Drapers’ Company binding book: “Thomas Rigg filius Rob[er]ti Rigg de Hauckshead in Com’ Lancastrie Agricol’,” apprenticed 3 Feb 1646/7 for nine years to Richard Barlowe, scrivener, of Tower Street, London; and the Hawkshead register: “bap: 1633 March xxv Thomas Rigg fil : Robti.” The authors call the identification with Thomas Riggs of Gloucester “very probabl[e]”. A Robert Rigge of Hawkshead Field, buried 5 Sept 1670, was “possibly” the father. Anderson inspected the original records in 2006.

Also used:

• Y-DNA (p. 125): two male-line descendants of Thomas Riggs Jr., “with classic genealogical proofs of descent from Thomas’s son, Thomas”, gave samples that matched descendants of Edward Riggs of Roxbury, so the two immigrants “have a close common ancestor”.
• Thomas Riggs’s notebook (p. 122), quoting the Boston Sunday Globe, 16 Mar 1913, p. 7: a pigskin book inscribed “Thomas Riggs, his Booke, 1656”, with 12 pages of shorthand no one could read and the verse “And if this booke whereon you Looke by Casualty be loste, restor to me, for I am he That knowe best what it Coste.” The authors could not find the notebook. The same article (p. 122 n. 14): “After his marriage he had a curious arrangement with his father-in-law [Thomas Millett], who paid Mr. Riggs for his board at the rate of two days’ labor a week.”
• Mary Millett’s birth (p. 120 n. 2), quoting the printing in NEHGR 5 (1851): 244: “Mary the daughter of Thomas Millet & Mary his wife was borne 27o (6o) 1639”, a day later than the Record Commissioners’ printing.