Section 424.01 - Scope and purpose(a) Part 424 provides regulations for revising the Lists of Endangered and Threatened Wildlife and Plants and designating or revising the critical habitats of listed species. Part 424 provides criteria for determining whether species are endangered or threatened species and for designating critical habitats. Part 424 also establishes procedures for receiving and considering petitions to revise the lists and for conducting periodic reviews of listed species.(b) The purpose of the regulations in part 424 is to interpret and implement those portions of the Act that pertain to the listing of species as threatened or endangered species and the designation of critical habitat. 81 FR 7438 , Feb. 11, 2016