63 



in diameter. These from their frequent union have assumed other 

 forms also, and particularly that approaching to an oval, resulting 

 from the formation of one trunk, by the junction of two or three 

 branches. 







The superior termination of these branches appears from one or 

 two, which have remained unchanged in their form, at one end of the 

 specimen, to have been a concave star of a very elegant figure, formed 

 by perpendicular plates converging from the circumference. The stars 

 are also plainly seen on the polished surface of the specimen. It is 

 there seen that the perpendicular plates, some much larger than 

 the rest, reach in a straight line to the centre, and that in the trian- 

 gular space between every two of these, are smaller plates which 

 pass from the circumference in different lengths towards the centre. 

 These smaller plates are decussated by other perpendicular plates 

 concentrically disposed, and thereby forming a species of net-work 

 within each small triangular cavity. This structure, not exactly in- 

 deed expressed in the engraving, gives to the stars a peculiar richness 

 of appearance, which is still farther increased by the alternately greater 

 and less projection of the ends of the straight plates beyond the peri- 

 phery of the circle formed by the most external of the concentric 

 plates. 



The fossil madrepores with distinct, finely striated branches, ter- 

 minating with the madreporean star, have been considered by the 

 earlier oryctologists as petrified reeds, (junci lapidei). Thus Mercatus 

 gives the representation of a madreporite of this kind under the de- 

 signation ofjuncus lapideus; but Lancisius remarks that this stony reed 

 of Mercatus differs very little from millepora Imperati. 



Madreporites bearing this reedy appearance are found in several 

 parts of this island. They are frequently met with in Derbyshire, of 

 two inches in thickness, and upwards of two feet in length. 



A small specimen of this kind of fossil madrepore from Derbyshire, of 

 rather a conical form, is figured at Plate VI. Fig. 2. Sufficient of the 



