London. It has the inventory number NHMUK 3775 (earlier BMNH R3775). It was found in a layer of the Tunbridge Wells Sand Formation dating from the Valanginian, about 137 million years old. This holotype is the best specimen and is composed of the front end of a skeleton minus most of the head and the forelimbs, though only the parts on the face of the stone block are easily studied. The block measures about 135 by 75 centimetres. The holotype consists of the rear of the skull and perhaps lower jaws, ten vertebrae, both scapulae, both coracoids and several spikes and armour plates. The skeleton is viewed from below. For a long time no further preparation had taken place, beyond the assembly and chiselling out by Mantell himself, but in the early twenty-first century the museum began to further free the bones by both chemical and mechanical means. This has proven difficult because the acids used tended to dissolve the glue and gypsum with which the fossils had been repaired, causing the blocks to fall apart. The limited information gained by the preparations by Mark Graham since 2003, was published in 2020, together with a revised description. Several finds from the mainland of Britain have been referred to Hylaeosaurus armatus. However, in 2011 Paul Barrett and Susannah Maidment concluded that only the holotype could with certainty be associated with the species, in view of the presence of Polacanthus in the same layers. Additional remains have been referred to Hylaeosaurus, from the Isle of Wight, (the Ardennes of) France, Bückeberg Formation, Germany, Spain and Romania. The remains from France may actually belong to Polacanthus and the other references are today also considered dubious. However, possible remains were reported from Germany in 2013: a spike, specimen DLM 537 and the lower end of a humerus, specimen GPMM A3D.3, which were referred to a Hylaeosaurus sp. Later species Hylaeosaurus armatus Mantell 1833 is currently considered the only valid species in the genus. However, three others have been named. In 1844, Mantell named Hylaeosaurus oweni based on the same specimen as H. armatus, wanting to honour Richard Owen. This has been sunk as a junior objective synonym of H. armatus. In 1956 Alfred Romer renamed Regnosaurus into Hylaeosaurus northhamptoni. Polacanthus Owen 1865 was by Walter Coombs in 1971 renamed into Hylaeosaurus foxii. These last two names have found no acceptance; H. foxii remained an