genus Castor vs mammal genus

genus Castor and mammal genus both are nouns.

Word	Noun	Adjective	Verb	Adverb
genus Castor	Yes	No	No	No
mammal genus	Yes	No	No	No

As nouns, mammal genus is a hypernym of genus Castor; that is, mammal genus is a word with a broader meaning than genus Castor:

genus Castor (noun)	mammal genus (noun)
type genus of the Castoridae: beavers	a genus of mammals