Page:The Geologist, volume 5.djvu/59



One of the commonest fossils of the chalk in the London district is the beautiful Sea-Urchin, of which we here give two figures, from examples in the national collection. It was named by Dr. Mantell, in honour of Mr. Charles König, the distinguished German savant, who in his youth was Librarian to Sir Joseph Banks, and became afterwards the Keeper of the Natural History Collections in the British Museum. By the country people in Wiltshire it is called the "Shepherd's Crown."

The König's Sea-Urchin belongs to a subdivision of the old Linnean genus Cidaris, to which the name of Cyphosoma was given by Agassiz (from, curvus; , corpus). The five ambulacral bands are nearly as broad as the inter-ambulacral, and are ornamented with a double series of tubercles equal in size to the rest. These tubercles are placed on crenulated bosses, but are not perforated as in most of the Cidaridæ.

The upper and under sides of this fossil Urchin are so different that drawings of them might be taken to represent two distinct species. The under side exhibits ten pairs of rows of tubercles, largest at the margin, and diminishing gradually to the central orifice. On the upper surface the tubercles are much smaller, and there are two additional rows on the inter-ambulacral bands, external to those which are continued downwards over the base. This character was pointed