Endowed, then, with acute vision which was trained to a high degree along certain lines, and gifted with the first glimmerings of artistic taste, prehistoric man learned to appreciate any conspicuous and attractive-looking fossil. That very common chalk fossil, which seems to have settled down finally to the name of _Porosphaera globularis_, and which is by general consent now regarded as a sponge, was a special favourite with men of the Barrow period. This small, spherical fossil, unfortunately nameless among common folk, occurs somewhat plentifully as a flint “pebble” in drift gravels which have originally been eroded from the chalk. Sometimes the _Porosphaera_ has a natural perforation, corresponding with one of its diameters, and thus the searcher could obtain a ready-made bead. By stringing together these fossils, a necklace was formed, and of these necklaces, the “threads” of which have perished, the number of flint “beads” found in the barrows supply convincing testimony. The salient fact is that, in several recorded instances, [Illustration: FIG. 60. Specimens of the fossil sponge _Porosphaera_ (= _Coscinopora_) _globularis_, with orifices artificially enlarged. A, B, C, sections of the fossil; A, with hole artificially enlarged at both ends; B, in the middle; C, at one end only. D, E, F, show the natural shapes of _Porosphaera_, and the attempts made to enlarge the openings. H, J, K, L, exhibit sections of the “beads,” which contained a little organic matter, probably the remains of the ligament by which the beads were strung. G is a perforated fossil shell. ] the fossils were found in groups; thus precluding natural agencies as a cause of their occurrence. In ordinary circumstances, the fossils would be isolated and scattered throughout the gravels somewhat sparingly. Moreover, Mr James Wyatt, who examined over 200 specimens of _Porosphaera_, believed, from markings which were visible when sections were cut, that in several cases the hole had been artificially enlarged with a drill[761] (Fig. 60). To enumerate barrows which have yielded this particular fossil would be wearisome, but another globular fossil, the beautifully ornamented echinoderm known as _Cidaris_, deserves a note. Evans records his having seen specimens of this fossil bored so as to form part of a Saxon necklace, and, in other cases, to serve as spindle-whorls[762].