by Craig_Thomas » Wed Jul 11, 2012 10:06 am
The genitive tells you that the stem is Aenēid- and that it belongs to the third declension, so: Aenēis, Aenēidem, Aenēidis, Aenēidī, Aenēide. (It might also be expected to follow the Greek declension with accusative Aenēida and genitive Aenēidos.)