Children of Daniel [sic, appears to be typo, accompanying text is about Samuel] Peirce [#23] and Rebecca Converse: 6) Ruth, b. 21 Nov 1728, m. James Thomas.
As cited, Pierce says that Ruth married James Thomas. Based on the text of his entry on sister Mary, (saying she is not mentioned in the probate record), this identification of Ruth's marriage may be based on a perusal of probate. It would also appear that Ruth is the "cousin Ruth Thomas" [i.e., meaning niece in colonial times] mentioned in the will of her uncle.
There is a birth in Boston of a daughter Joanna to James and Ruth Thomas in Boston 1747. There is a James Thomas in Salem who has a daughter Ruth bp. 1752 (plus other children, and d. 1803, aged 83). There is a marriage in Scituate of James Thomus and Ruth Brooks in "174[8]". These records need to be sorted out to see which, if any, or perhaps all, apply to this Ruth.