Arthraster cristatus (Spencer)
This exceptionally rare form of Arthraster from the White Chalk is distinguished from Arthraster dixoni by the crater-like pits on the central ridges of the ossicles.
1). Type specimen; reconstructed arm portion, viewed (A) aborally and (B) laterally (from the side); (x4.0, Seaford Chalk, Micheldever, Hampshire, BMNH (British Museum (Natural History) London) E20266. Images © 2005 The Natural History Museum, by kind permission.
2). Detail of the above specimen; each ossicle possesses a central ridge ornamented with crater-like pits, some of which are rimmed (x8.0). Image © 2005 The Natural History Museum, by kind permission.