Promicroceras planicosta are an extinct species of ammonite which lived in the lower lias of the Jurassic period, between 200 to 174 million years ago, they are well known and sought after due to their evolute shells, which exhibit strong, deep ribbing. The shells also show an open umbilicus (centre of the coil), though this cannot always be viewed, as the centres of ammonoid shells are often the most fragile part. They can be found across Europe in marine strata, particularly abundant within other Jurassic rocks in the South west of England. One of the main sought after points of these ammonite fossil specimens, particular from the UK is that the shells have been agatised during fossilisation, giving them a pearly lustre. Overall, the shells are not too large, our stock exhibits the shells still within their matrix, sizes of the actual specimen are between 15 to 25 mm in diameter, where as the size of the matrix will vary. Each piece will come supplied in a card tray with an information label.