Trigonoceratidae comprise members of the order Nautilida characterized by a loosely coiled to evolute shell generally bearing longitudinal ribs or ridges with a whorl section that is oval to subquadrate and varying from compressed (squeezed) to depressed (flattened).

The Trigonerceratidae were derived from the core Centroceratidae (basis for the name Centroceratina) early in the Mississippian along with the longer lived Grypoceratidae.

It is the only genus included that has a subtriangular whorl section consisting of a broad concave venter and narrow dorsum.

Those with straight or slightly sinuous sutures are Apogonoceras, Diodoroceras, Discitocdras, Rineceras, Stroboceras, and Thrincoceras; with a discernible ventral lobe: Aphelaeceras, Epistroboceras, Lispoceras, Maccoyoceras, Pararineceras, Subclymenia, and Vestinutilus; and with a ventral saddle: Chouteauoceras and Leuroceras.

Ventral saddles are also found in the Centroceratidae in Carlloceras and Phacoceras, in the Grypoceratidae in Stenopoceras and Parastenopoceras, and in the Syringonautilidae.