This mature Psiloceras planorbis displays vivid flashes of red, bronze, green, and golden iridescence, making it one of the most visually striking British Jurassic ammonites. Measuring 6.5 cm in diameter, the shell retains crisp, well-defined whorls, with its elegant spiral growth beautifully preserved across the matrix. The surrounding limestone slab is itself display-worthy, featuring two additional partial iridescent ammonites that add depth and interest to the piece. Psiloceras planorbis is the defining index ammonite of the base of the Jurassic Period, marking the dawn of this new era in Earth’s history. Recovered from the Somerset Jurassic Coast near Watchet, the specimen has been stabilised with a museum- standard 5% Paraloid B-72 conservation coating, applied sparingly to enhance preservation and protect surface detail. A rare combination of vivid natural beauty and scientific significance, this ammonite is ideal for display or study. Specimen Details Species: Psiloceras planorbis Diameter: 65 mm Matrix Size: Approx. 150 × 150 × 25 mm Age/ Era: Lower Jurassic. ~ 199–203 million years old Stratigraphy: Lower Lias, Hettangian Age: Circa 199–203 million years Locality: Beach find, near Watchet, Somerset, England Formation: Somerset Jurassic Coast Conservation: Stabilised with 5% Paraloid B-72 (museum standard) Condition: Excellent, very well preserved, with natural red, bronze, green, and golden iridescence. No restoration; only professional preparation and conservation.