Just add the S.
hippo-cr-it
The plural form of him, her, or it is them. (objective pronouns)
Italy does not have a plural form.
The plural form of beauty is beauties.
The plural form is spelt : subpoenas.
The plural form of quiz is quizzes.
The plural form of radius is radii.
Trout is plural
The plural form of the noun 'sea' is seas.
The plural form for the noun coach is coaches.
The plural form for the noun index is indexes.
The plural form of "atlas" is "atlases."
The plural is Tuesdays. No apostrophe.