Loosely coiled; early whorls typically irregularly helical; later whorls with several, more or less straight shafts in one plane, but some are helical throughout. Ventrolateral tubercles normally on at least some ribs and commonly lateral tubercles as well.

Coiled in open spiral, in one plane or slightly helicoid, with terminal hook or with several more or less straight shafts; ribs rectiradiate, weak or absent on dorsum, with ventrolateral and in some species midlateral tubercles on some or all ribs; ribs joining tubercles across venter may be flattened but not doubled.

with three subparallel shafts; ribbing on phragmocone oblique; fine or almost obsolete; ribs of phragmocone on and between periodic, strong folds or with periodic, large flat spine bases covering several ribs; on body chamber ribs bolder and distant; tuberclesw, if persisting, covering only 1 rib. Suture more florid than in Protanisoceras.

Differs from Protanisoceras primarily in its more helicoid coiling, fibulate ribbing, and more complex suture with regularly bifid L and U; occasional subtrifid lobes occur.

Coiling rather irregular, in one plane; ribs radial or oblique, with a pair of ventral tubercles joined normally only by single rib on venter; lateral tubercles rarely present.

Reference:

Wright C.W. 1996. Treatise on Invertebrate Paleontology; Part L MOLLUSCS 4 Revised (Volume 4: Cretaceous Ammonoidea)