Here is an assortment of figures of various specimens, all belonging to a species pertaining to tomorrow's Taxon of the Week (attribution to follow):
In the lower figure the whorl height is 3.2 cm. Because the general kind of organism involved is fairly obvious, I'm going to ask for a reasonable amount of specificity to count as a successful ID. But to give you a hand with being specific, I'll at least tell you that the age of the specimens is lower Upper Bathonian (during the Jurassic).
Update: Identity now available here. Upper figure from Rawson (1982); lower figure from Poulton (1987).
23 hours ago in The Phytophactor