Page:The Geologist, volume 5.djvu/60

42 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.