A class that doesn't work is not a class

http://en.wikipedia.org/wiki/Biological_classification

http://en.wikipedia.org/wiki/Class_%28biology%29

Mammals (formally Mammalia /məˈmeɪli.ə/) are members of a class of air-breathing vertebrate animals characterized by the possession of hair, three middle ear bones, and mammary glands functional in mothers with young.[...]http://en.wikipedia.org/wiki/Mammalia