Cyrtoceras

{{Short description|Extinct genus of nautiloid}}

{{For|the plant species also known as Cyrtoceras elegans|Hoya celebica}}

{{Automatic taxobox

| fossil_range = {{fossil range|Middle Ordovician|Middle Devonian|ref={{cite journal |doi=10.2183/pjab.63.135 |journal=Proceedings of the Japan Academy, Series B: Physical and Biological Sciences |volume=63 |issue=5 |pages=135–138 |year=1987 |title=The Ancestry of the Cephalopoda: From Helcionella to Plectronoceras |author=Teiichi KOBAYASHI |doi-access=free |bibcode=1987PJAB...63..135K }}}}{{dead link|date=July 2012}}

| image = Cyrtoceras NT small.jpg

| image_caption = Digital life restoration of "Cyrtoceras sp"

| taxon = Cyrtoceras

| authority = Conrad, 1838

}}

Cyrtoceras is an dubious extinct genus of oncoceridan nautiloids that was used for fossils from the middle Ordovician to the middle Devonian, in Africa, Europe, North America and South America.

As for 1964, this genus is no longer considered as valid, as it has not been correctly established.{{Cite journal |last=Teichert |first=C. |last2=Kummel |first2=B. |last3=Sweet |first3=W. C. |last4=Stenzel |first4=H. B. |last5=Furnish |first5=W. M. |last6=Glenister |first6=B. F. |last7=Erben |first7=H. K. |last8=Moore |first8=R. C. |last9=Nodine Zeller |first9=D. E. |date=1964 |title=Cephalopoda – general features, Endoceratoidea – Actinoceratoidea – Nautiloidea – Bactritoidea In R. C. Moore (Ed.), Treatise on Invertebrate Paleontology, Part K, Mollusca 3 |url=https://journals.ku.edu/InvertebratePaleo/issue/view/467 |journal=Lawrence: The University of Kansas Press |pages=1-519}}{{Cite journal |last=Afhüppe |first=Lukas |last2=Becker |first2=R. Thomas |date=2022-09-01 |title=A new discosorid and some other nautiloids from the Givetian of the Rhenish Massif, Germany |url=https://link.springer.com/article/10.1007/s12549-022-00541-3 |journal=Palaeobiodiversity and Palaeoenvironments |language=en |volume=102 |issue=3 |pages=613–627 |doi=10.1007/s12549-022-00541-3 |issn=1867-1608|doi-access=free }}