362 CLYPEUS 



Description. — This well-known and widely distributed urchin was first figured by 

 Dr. Plot in his ' History of Oxfordshire,' tab. ii, figs. 9, 10, and was accompanied with the 

 following quaint remarks : 



" Of Brontia, therefore, or Omhria (call them which you will), we have several sorts 

 in Oxfordshire, which yet all agree in this, that they are a sort of solid irregular hemi- 

 spheres ; some of them oblong, and having somewhat of an oval ; others either more 

 elevated, or depressed on their bases. All of them divided into five parts, most times 

 inequal, rarely equal, by five rays issuant from an umbilicus or center, descending from it 

 down the sides of the body, and terminating again somewhere in the base. They are 

 never found in beds together, like some other formed stones, nor that I have yet heard of 

 (says the ingenious Mr. Kay*) in great numbers in one place : but in the latter I must 

 take leave to inform him, that though I think it in the main to be true, yet that at 

 Tangley Pulbrook, and all about Burford, they are found in such plenty, that I believe it 

 were easy in a little time to procure a cart-load of the first sort of them, carefully 

 exhibited in tab. ii, figs. 9, 10, whose innermost texture, though it seem to be nothing 

 more than a coarse rubble-stone, yet is thinly cased over with a fine laminated substance 

 (the plates lying obliquely) much like Lapis Judaicus. In form they are flat, depressed 

 upon the basis, in colour generally yellow, their rays made of a double rank of transverse 

 lines, with void spaces between the ranks, visible enough on the top of the stone (fig. 9), 

 but not so distinguishable on the bottom (fig. 10) ; the whole body of the stone, as well 

 as the spaces included within the rays, being elsewhere filled with annulets much more 

 curiously wrought by nature than by the tool of the graver. 



" The center of these rays, by Pliny called modiolus, by Aristotle umbilicus, is never 

 placed on the top of the stone, but always inclining to one side, as that at the bottom does 

 to the other ; the axis lying obliquely to the horizon of the stone. Which gave occasion 

 to a learned Society of Virtuosi, that during the late usurpation lived obscurely at 

 Tangley, and had then time to think of so mean a subject, by consent to term it the Polar- 

 stone, having ingeniously found out by clapping two of them together, as suppose the 

 figs. 9 and 10, that they made up a globe, with meridians descending to the horizon, and 

 the pole elevated, very nearly corresponding to the real elevation of the pole of the place 

 where the stones are found. "f 



Klein j gave the following diagnosis of this urchin : " Species 1, Plotii ; maximus discum 

 referens; Burfordinensis, Hist. Oxon., tab. ii, figs. 9, 10. Luydii prope Fulbrock in agro 

 Oxon. Integra testa intra demissos circulos stellata, superficiem quinque, taeniae profundae 

 duplicatae ac crenatae et unus altus sulcus laevis in undecim, basin vero quinque sulci 

 angustiores in totidem segmenta dividunt," In tab. xii, this author figured a large 



* 'Observations Topograph.,' p. 116. 



t Plot's 'History of Oxfordshire,' pp. 90, 91. 



X 'Naturalis Dispositio Echinodermatuni,' p. 22. 



