Choanoceratidae

Choanoceratidae is a family of upper Silurian nautiloids included in the Ascocerida, named for the genus Choanoceras. Shells are slightly curved with a gradual rate of expansion. Septa form deep asymmetrical cones. Siphuncles are subcentral. The body chamber in the mature ascoceroid section is large in proportion to the phragmocone retained.

References: W.M. Furnish and Brian F. Glenister, 1964. Nautiloidea - Ascocerida. Treatise on Invertebrate Paleontology, Part K.