The genus is part of the Classification system in use in all the Creatures series games.
The genus is the second number in the classification system, and defines the category to which any particular object belongs. Creatures will call any object in the same genus by the same name and, due to the limitations in their brain structure, cannot differentiate between objects beyond this level. For this reason it is important to make all COBs or agents in the same genus behave in similar ways so that creatures can learn about their world effectively.
As creatures are effectively "blind," and in C3/DS navigate by smells emitted by the CAOS script of an object, and the fact that there are actually very few smells (Cellular Automata) that creatures understand, they will be unable to tell the difference between any given two toys.
The plural of genus is "genera."