Promicroceras planicosta Sowerby.
Calcite septaria. In the centre are a cluster of 3d Ammonites some with the original white shell preserved.
Jurassic, Upper Sinemurian, Obtusum Zone, 'Ammonite Marble'.
Marston Magna, Somerset.
Septaria : 8 x 6.3 x 3.5 cm.
