Promicroceras planicosta Ammonite, from Moumouth Beach, Lyme Regis, UK (No.155)

Promicroceras is a species of Ammonite is found in rocks of Lower Jurassic age and came from Europe.

This genus is characterised by an evolute shell, with the individual whorls overlapping only slightly; all the whorls are clearly visible. In cross-section the whorls are rounded. Thick, well-spaced ribs cross the shell and radiate from the central umbilicus. As the ribs reach the ventral surface they curve slightly and become flattened.