Albert Barnes Commentary 1 Chronicles 9:31

"And Mattithiah, one of the Levites, who was the first-born of Shallum the Korahite, had the office of trust over the things that were baked in pans." — 1 Chronicles 9:31 (ASV)

Mattithiah, the firstborn of Shallum the Korahite — This Shallum seems to be the person mentioned in 1 Chronicles 9:19, whose actual firstborn was Zechariah (1 Chronicles 26:2). Mattithiah may have been his eldest lineal descendant at this time.