Cyrtonybyoceras is a genus of slightly exogastric members of the Wutinoceratidae, a family of actinocerids and probably derived from an earlier Wutinoceras .

The siphuncle is ventral but not marginal, in general form like that of Nybyoceras.

Upper and lower septal necks are recumbent or narrowly free.

Cyrtonybyoceras is so far known only from the Whiterock Stage in North America.

It has also been found in the Antelope Valley Limestone in the Toquima Range in Nevada.