The Weyland–Yutani Extrasolar Species Catalog was a guide concerning various alien species compiled by the Weyland-Yutani Corporation. Though it was widely known on the Frontier, a number of species were left out of the publication; these included Anathemas, on the grounds that no official specification could be applied to them, and creatures classified under the Company's XX bracket such as Xenomorphs and Proto-Xenomorphs.