We have offered some amazing and rare specimens of prehistoric marine and this remarkable fossil is certainly no exception. It is an extraordinary LARGE block of an entire layer of intensely packed sea urchins in rare preserved form with their spines, from the Middle Jurassic. The species is called Acrosalenia hemicidaroides. This is not a fossil found from any commercially mining operation and was privately collected making it unique and likely a one-of-a-kind find likely not to be repeated. We have seen very small fragments of this layer available for sale for hundreds of dollars but never a specimen anywhere near as large as this giant and UNBROKEN layer block. The entire block is a large portion of the entire layer and the sea urchins and spines fill this entire large thick specimen. A piece like this is certainly the perfect candidate to be the centerpiece for any very advanced fossil collection. Many sea urchin fossils with spines are prepared with acid which dissolves the matrix and loosens the spines so that they come off the plate. The spines are then reassembled around the central portion called a TEST, to restore the appearance of the urchin. Such specimens are unnatural and we have seen several on the market in the recent past.