a. Greek neuters with nominative singular in -a (as poéma) frequently end in -ís in the dative and ablative plural, and rarely in -órum in the genitive plural; as, poématís (for poématibus), poématórum (for poématum).
b. A number of monosyllabic nouns with mute stems want the genitive plural (like cor). See §103. g. 2.