50 CFR 17.50 - General.
(a) Whenever a species which is not Endangered or Threatened closely resembles an Endangered or Threatened species, such species may be treated as either Endangered or Threatened if the director makes such determination in accordance with section 4(e) of the Act and the criteria of paragraph (b) of this section. After the Director has made such determination in accordance with the notification procedures specified in the Act, such species shall appear in the list in § 17.11 (Wildlife) or § 17.12 (Plants) with the notation “(S/A)” (similarity of appearance) in the “Status” column, following either a letter “E” or a letter “T” to indicate whether the species is being treated as Endangered or Threatened.
(1) The degree of difficulty enforcement personnel would have in distinguishing the species, at the point in question, from an Endangered or Threatened species (including those cases where the criteria for recognition of a species are based on geographical boundaries);
(3) The probability that so designating a similar species will substantially facilitate enforcement and further the purposes and policy of the Act.