§43. Case-Forms in the First Declension

a. The genitive singular anciently ended in -āī (dissyllabic), which is occasionally found: as, aulāī. The same ending sometimes occurs in the dative, but only as a diphthong.

b. An old genitive in -ās is preserved in the word familiās, often used in the combinations pater (māter, fīlius, fīlia) familiās, father, etc., of a family (plur. patrēs familiās or familiārum).

c. The Locative form for the singular ends in -ae; for the plural in -īs (cf. p. 34, footnote): as, Rōmae, at Rome; Athēnīs, at Athens.

d. The genitive plural is sometimes found in -um instead of -ārum, especially in Greek patronymics, as, Aeneadum, sons of Æneas, and in compounds with -cŏla and -gĕna, signifying dwelling and descent: as, caelicolum, celestials; Trōiugenum, sons of Troy; so also in the Greek nouns amphora and drachma.

e. The dative and ablative plural of dea, goddess, fīlia, daughter, end in an older form -ābus (deābus, fīliābus) to distinguish them from the corresponding cases of deus, god, and fīlius, son (deīs, fīliīs). So rarely with other words, as, līberta, freed-woman; mūla, she-mule; equa, mare. But, except when the two sexes are mentioned together (as in formulas, documents, etc.), the form in -īs is preferred in all but dea and fīlia.