Systematic Paleontology
Order Bactritida
Family Bactritidae
Genus Cyrtobactrites
Cyrtobactrites is a bactritid, named by Erben in 1960, that lived during the Early Devonian, found in the lower Devonian of northern France and Germany. The shell (conch) is curved exogastrically, the venter with siphuncle on the outer convex side. Whorl section is narrowly oval. Growth lines indicate a ventral sinus - for the hydro-jet hyponome, and lateral sinuses - for the eyes. Sutures form ventro-lateral saddles. A dorsal saddle, in the inner, concave surface, is slightly developed or lacking.
Cyrtobactrites is derived from Lobobactrites and in turn is ancestral to the ammonoids.
References
H. K. Erben 1964. Bactrioidea. Treatise on Invertebrate Paleontology, Part K. Cyrtobactrites, fig 358.7, p. K500 & p. 501