Complex sentence: Genitive singular of these nouns ends in-αο or-εω, rather than-ου, eg, Ἀτρεΐδαο, as opposed to Ἀτρεΐδου.
Split into simpler sentences: Genitive Singular of these nouns ends in-αο or-εω, rather than-ου. For example, Ἀτρεΐδαο, as opposed to Ἀτρεΐδου.