The Latin masculine noun collis (a hill) has a singular genitive collis and a plural genitive collium.

The genitive case is used to show possession or relationship between nouns in a sentence. It can also indicate the origin or material of something.

The Latin masculine noun tumulus (a rounded hill, a burial mound or grave) has the genitive singular tumuli and genitive plural tumulorum.

Animalis is the genitive of "animal", which means "animal". (In the genitive = "of the animal".)

The form farmers' is the plural possessive form.