Calycoceras

Calycoceras spinosum, from here.

Belongs within: Acanthoceratoidea.

Calycoceras is a genus of evolute ammonites with depressed whorls known from the Upper Cretaceous (Cenomanian) (Wright et al. 1996).

Characters (from Wright et al. 1996): Rather evolute, with whorl section depressed and subcircular, oval, polygonal, or subquadrate; ribs strong, generally straight, continuous over rounded or flat but not concave venter; on early whorls at least umbilical, ventrolateral, siphonal, and, in most specimens, midlateral tubercles; in multituberculate forms umbilical tubercle more prominent than midlateral; tubercles may disappear with age and may or may not be rejuvenated on last part of shell. Marked dimorphism in size apparently general.

<==Calycoceras
    |--C. andranovaritelense K79
    |--C. asiaticum K79
    |--C. boulei K79
    |--C. canitaurinum K79
    |--C. hourcqi K79
    |--C. jeanneti K79
    |--C. latelobatum K79
    |--C. leonense K79
    |--C. (Calycoceras) naviculare (Mantell 1822) [=Acanthoceras naviculare] KK08
    |--C. newboldi K79
    |--C. orientale K79
    |--C. spinosum K79
    |--C. stoliczkai K79
    `--C. tarrantense K79

*Type species of generic name indicated

REFERENCES

[K79] Kauffman, E. G. 1979. Cretaceous. In: Robison, R. A., & C. Teichert (eds) Treatise on Invertebrate Paleontology pt A. Introduction. Fossilisation (Taphonomy), Biogeography and Biostratigraphy pp. A418–A487. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[KK08] Kennedy, W. J., & H. C. Klinger. 2008. Hypermorphosis in Salaziceras, a Cretaceous ammonite, from Madagascar. African Natural History 4: 113–116.

Wright, C. W., J. H. Callomon & M. K. Howarth. 1996. Treatise on Invertebrate Paleontology pt L. Mollusca 4, Revised vol. 4. Cretaceous Ammonoidea. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).