Nucula is genus of salt water bivalves which belong to the clam family, they are fairly small in size, even the modern day species, with these fossil specimens measuring around 1 to 1.5 cm in size. These are also not the actual fossil shells themselves, but a trace fossil, of the internal mould of the animal. An internal mould is often formed when the animal becomes fossilised and the inside of the shell also fills with sediment, which over time lithifies into rock. After which the outer shell begins to erode away, leaving the internal mould only present. These are of Jurassic age, between 200 to 145 million years old. They were found in the Cordatum zone of the Oxford clay at Weymouth, Dorset, UK. The specimens will come supplied in a packet with a label.