Polygrammoceras is an orthoconic nautiloid that lived during the period from the middle Ordovician to the early Devonian in what is now North America and Eurasia.

The Polygrammoceras shell bears longitudinal ribs or striae separated by narrow grooves or flat shallow inner areas. As common for orthocerids

Orthocerida

Orthocerida is an order of extinct nautiloid cephalopods also known as the Michelinocerda that lived from the Early Ordovician possibly to the Late Triassic . A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous...

sutures are straight and transverse. The siphuncle is between the center and the venter, and is empty of organic deposits with segments expanded into the chambers.

References

• Sweet, Walter C. 1964. Nautiloidea-Orthocerida. Treatise on Invertebrate Paleontology, Part K. Geological Soc of America, and Univ Kansas Press.
• Polygrammoceras Paleobio db