The Family PRIONITIDAE is a nightmare of taxonomy. The amount of intraspecific variation, or even intrageneric variation is overwhelming. Most generic assignments are based on the shape, size, amount, and/or lack of ribs, bullae, nodes, whether they cross the venter or stop short, whether the nodes are mid flank or start near the umbilicus, whether the inner whorls or the outer whorls are smooth. A lot of specific and generic assignments are arbitrary, a slightly arched venter instead of a flat venter is cause for different generic assignment of forms that basically look exactly alike.
Tozer, 1994, in his monograph of Canadian Triassic Ammonoids, discussed the differences between Population Taxonomy and Typological Taxonomy and admitted that his classification, especially of the Prionitidae, was arbitrary, and to use a strictly typological taxonomy would mean almost every specimen was a seperate species. He also talked about using the typological method just to show what the taxon looked like.
To see a Prionitid, it is easily assigned to the Prionitidae, and the
beds containing it are easily assigned to the Late Smithian, and usually
to the biozone and/or beds known for the Prionitidae. Is it really necessary to split them into a bunch of different species or genera? I suppose I could live with a few nominal species divided amongst a few genera for the time being, at least until the family is revised and a more natural classification determined. Still, what a Prionite-mare.
For references see THIS old post, along with an old rant of the same topic. ;)