The Geologist/Volume 5/Note on König's Sea-Urchin. (Cyphosoma Kœnigi, Mantell.)
Fig. 1.
Fig. 2.
CYPHOSOMA KŒNIGI.
[From the Upper Chalk of Gravesend, Kent.]
In the National Collection, British Museum.
THE GEOLOGIST.
FEBRUARY 1862.
NOTE ON KÖNIG'S SEA-URCHIN. (Cyphosoma Kœnigi, Mantell.)
By S. P. Woodward, F.G.S.
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 κυφὸς, curvus; σῶμα, 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 out by Dr. Mantell in his original description of the species, and serves to distinguish it from another form, nearly equally common in the chalk, which is figured and described by Goldfuss as C. granulosus, but is generally regarded as a (perhaps sexual?) variety, having a more tumid shell, and with the additional rows of tubercles on the upper surface rudimentary or obsolete.
The pairs of ambulacral pores in Cyphosoma Kœnigi, form ten winding lines from the mouth-opening (peristome) to the apical orifice (periproct). They are somewhat crowded at the mouth, but extend in single file to a little above the circumference, and then fall into double series on the upper part of the shell. The specimen represented by fig. 1 exhibits a portion of the dental apparatus, lying in the peristome, and consisting of one of the five pairs of jaws which are similar in all the Echinidæ, and form the 'lantern' of Aristotle.
Young and half-grown specimens of Cyphosoma Kœnigi are comparatively rare. They may be recognized by the flatness of the under surface, which distinguishes them at all ages, while in the little C. corollare (Parkinson) the base is rendered concave by the curling inwards of the margin of the peristome. In the other common little species, C. spatuliferum (Forbes), the ambulacral pores are ranged in single file throughout their course.
The spines of Cyphosoma Kœnigi are awl-shaped and rather short and stout, with spatulate ends. In the second example figured, a multitude of spines of all sizes were preserved in connexion with the shell, and have been cleared from the matrix with great skill and ingenuity by Mrs. W. H. Allen.
There is another specimen in the British Museum with the spines remaining in situ, which was obtained more than a century ago, and formed one of the ornaments of Sir Hans Sloane's collection.
Although common in the chalk-pits of the Thames Valley, and in those near Brighton and Lewes, the Cyphosoma Kœnigi appears to be unknown to the collectors of fossils from the uppermost division of the chalk at Norwich, or in the corresponding bed at Ciply in Belgium, and Meudon near Paris. It is said to be found at Montolieu, in the department of Drome, at Dusseldorf, and in the island of Rugen in the Baltic.