In the course of a re-investigation into the vexed question of the origin and nature of Chalk flints, the very natural suggestion occurred to me that the remains of a fresh water sponge might probably be found in the “flints” of the Purbeck limestones, and a recent visit to Lulworth afforded the opportunity of verifying the conjecture. Patches of spicules with valves of Cypris, etc., etc., occur in most of the specimens then obtained.