What is "asymptoceras"

Asymptoceras is an aipoceratid genus (Nautiloidea) similar to Aipoceras but tightly coiled and with only part of the body chamber divergent from the previous whorl. Shell evolute, expanding fairly rapidly; umbilicus open, perforate; whorl section ovoid to subquadrate.

Asymptoceras is known from Mississippian (Lower Carboniferous) sediments in Europe and North America.