44 



the diameter in one direction that it possesses in another. By a mo- 

 derate stroke against the side of one of these angular columns, one or 

 more of them may be detached from the general mass. The sides 

 of these columns will' be found to be finely and closely striated lon- 

 gitudinally, the striae being intersected by very fine and closely set 

 transverse ridges. In those specimens in which the apices of the 

 columns happen to be complete, they are concave, and have a pro- 

 minent star, one third of the diameter of the concavity, arising out of 

 its centre. 



A careful examination of the beautiful web-formed star, which is ren- 

 dered visible in every column, by a transverse polished section, as well as 

 the striated plumose appearance which is manifested by a longitudinal 

 section, shews the internal structure of the stone, and of course the 

 curious fabric of the madrepore from which it derived its origin. 

 Numerous and exceedingly slender longitudinal lamellae correspond- 

 ing with the external striae, are seen disposed perpendicularly from 

 the circumference to the centre in a stellated form ; which are inter- 

 sected by proportionally numerous and equally delicate lamellae, per- 

 pendicularly disposed nearly in concentric circles : other lamellae, 

 answering to the external transverse ridges passing horizontally through 

 both sets of the perpendicular lamellae. From the curious arrange- 

 ment of these, and from their extreme minuteness and delicacy re- 

 sults that particular figure which has been by different authors so aptly 

 compared with the texture of the spider's web. Mr. Da Costa, speak- 

 ing of this fossil, says, " When polished, all these angular columns shew 

 themselves on the surface, in a fine net-work of heptagonal, hexagonal, 

 pentagonal, &c. meshes, and each mesh is adorned with a fine radiated 

 star in it ; and what with the beauty of the network and stars, and 

 exquisite polish and fine surface it is capable of, it is as elegant a 

 fossil as any of the fossil kingdom*. 



* A Natural History of Fossils, by Emanuel Mendes Da Costa. Vol. I. P. 247. 



