Barnesoceras

Barnesoceras Temporal range: Early Ordovician
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	Nautiloidea
Superorder:	Plectronoceratoidea
Order:	Ellesmerocerida
Family:	Ellesmeroceratidae
Genus:	Barnesoceras Flower, 1964

Barnesoceras is a moderately large, Lower Ordovician ellesmoerceratid genus with a simple, but strongly cyctoconic shell that expands in the vertical dimension more rapidly than in the horizontal, resulting in its being laterally compressed. The aperture is simple, unconstricted, and straight sided from in front. Growth lines show a broad crest on either side that swings forward above the ventral hyponomic sinus. Septa are close spaced and have a shallow curvature. The body, or living, chamber takes up much of the shell. The siphuncle is ventral, close to the longitudinally concave side.

All eight species named and described, including the type, Barnsoceras clavum Flower, 1964, were found in the Threadgill Limestone of the Lower Ordovician Tanyard Formation in Texas.

References

• R.H. Flower, 1964. The Nautiloid Order Ellesmeroceratida (Cephalopoda). Memoir 12. New Mexico Bureau of Mines and Mineral Resources, Socorro NM.