"His are small. Theirs are big."
Translation:Zȳha byka issi. Pōja rōva issi.
It's the Terrestrial plural. In this context, zȳha is the plural of zȳhon "his," and pōja is the plural of pōjon "theirs." The possessive pronouns (mine, yours, etc.) are Terrestrial, so their plural forms that end in -a and the adjectives likewise have the Terrestrial endings.