Antigyroceras is a genus of nautiloids in the order Discosorida, known from central Asia, that lived during Late Silurian and Early Devonian times. It is contemporary with the discosorid Endoplectoceras.
References
Sepkoski, J.J. Jr. 2002. A compendium of fossil marine animal genera. D.J. Jablonski & M.L. Foote (eds.). Bulletins of American Paleontology363: 1–560. Sepkoski's Online Genus Database (CEPHALOPODA)