Figure 2.

Images of nautilus shells and petrified echinoids. (a) Hooke's drawing of nautilus shells, intended to demonstrate the morphological similarities with the ‘snake-stones’ in figure 1a. (British Library, Ms Add. 5262, no. 153. Paper size 169 mm × 196 mm. Copyright © British Library Board; reproduced with permission.) (b) Intaglio table of nautili and fossilized echinoids. ‘Fig. 10’ in the drawing (figure 2c) was moved next to ‘fig. 9’, allowing a direct comparison between petrified and non-petrified objects. (R. Hooke, Posthumous works (1705), Tab: IIa and Tab: IIIa, between pp. 284 and 285, plate size 324 mm × 211 mm. Copyright © The Royal Society.) (c) Hooke's drawing of ‘helmet stones’ and ‘button stones’, which he described as filled ‘Echini shells’ (i.e. petrified echinoids). At ‘fig. 10’ Hooke showed a type of (contemporary) echinoids commonly found in Devon or Cornwall. Traces of red powder can be observed in the area around ‘fig. 6’ of the drawing. (British Library, Ms Add. 5262, no. 154. Paper size 231 mm × 190 mm. Copyright © British Library Board; reproduced with permission.) (Online version in colour.)