Deltocymatoceras is an involute cymatoceratid (Nautilioidea-Nautilida) with broadly arched whorl sides, strongly convergent on a narrow venter that bears a slight, rounded, keel-like ridge, and with no distinct ventro-latera shoulders.

Deltocymatoceras is probably derived form Cymatoceras by a rounding of the ventro-lateral shoulders resulting in a narrowing of the venter, coupled with the development of a pointed ventral saddle.

Eucymatoceras from the Lower Cretaceous is similar, except for lacking the vernal keel.

Contemporary, Upper Cretaceous Epicymatoceras is involute, discoidal.

Deltoidonautiluds with its similar name, and converging sides, belongs to the Hercoglossidae.