Greek Grammar

...they are, according to the consistency of the perittosyllabic declension, they also have the accusative case as perittosyllabic ending in -a. For example, krēpis boot, krēpidos, krēpida; chlamys, chlamydos, chlamyda.
But if they are barytone not having an acute accent on the last syllable, they have the accusative case not only perittosyllabic ending in -a, but also isosyllabic having the same number of syllables ending in -n. The Paris, Paridos, Parida and Parin.
Likewise, the mēnis, mēnidos, mēnida and mēnin; epēlys foreigner, epēlydos, epēlyda and epēlyn for both genders.

Concerning the vocative case.

Note concerning the vocative case: that generally the Attics have the same forms for the nominative and the vocative. And also for neuter nouns, generally the nominative, accusative, and vocative are the same. Apart from these, those that are declined isosyllabically, if they end in -as, as in the first declension, they form the vocative by the removal of the sigma. Similarly, those that are declined isosyllabically ending in -ēs, as in the same first declension, behave the same way, unless they are derived from a verb, or contain a tau, or are ethnonyms, in which case they form the vocative by the removal of the sigma.