Coiling rather irregular, typically in open, plane spiral ending in 2 or 3 more or less parallel shafts; early part may be helical. Section circular to compressed; ribs annular or interrupted on dorsum; no tubercles. The earliest hamitids, some with subtrifid L, appear in the upper Lower Albian and are presumably derived from early Anisoceratidae by loss of tubercles.

Typically with 3 well-separated, subparallel shafts, but initial spiral or even helical coiling may persist; whorl section circular, depressed or compressed; straight, rectiradiate or oblique ribs typically fine and dense to coarse and distant, but may be obsolescent.

Reference:

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