Verse 31 follows the summarizing formula of verse 5 (see comments there) and verse 20.

These are the sons of Shem: These now refers back to all the names in verses 21-30. See verses 5 and 20 for the translation of this formula.

Quoted with permission from Reyburn, William D. and Fry, Euan McG. A Handbook on Genesis. (UBS Helps for Translators). New York: UBS, 1997. For this and other handbooks for translators see here .