What is "hesperoceras"

Hesperoceras is an orthocerid cephalopod belonging to the subfamily Michelinoceratinae which comes from the lower Mississippian of New Mexico.

Hesperoceras has a straight, orthoconic, shell with a subrectangular cross section. The sutures are straight and transverse on the narrow sides but form broad rounded lobes on the wide sides, and the siphuncle is small and central.