216 CHAPTER OF CRITICISM. 



Each crystal invariably occupies a separate plate, its base never extending 

 over a suture. They are consequently disposed in rows, the size of each crystal 

 diminishing from the base towards the apex of the Echinus. Now, wherever 

 the chalk formation contains flint nodules in any considerable quantity, a certain 

 proportion of the Echini have their cavities filled with silex, and if by natural 

 or artificial means the shell (which is not itself silicified) be removed, we obtain 

 a very accurate cast of the interior. These siliceous casts are generally 

 abundant wherever the chalk has been abraded by currents of water, the im- 

 bedded flints being left in the form of superficial gravel. It is obvious 

 that a deposition of calcareous crystals, in the cavity of an Echinus, would be 

 no obstacle to a subsequent infiltration of silex, but a cast formed under these 

 circumstances, instead of presenting elevations, corresponding to the sutures and 

 ambulacra! perforations of the shell, would exhibit the impression of these 

 crystals. The history, therefore, of the Honey-comb Echinites is readily under- 

 stood, but the existence of the crystals is, perhaps, deserving of some further 

 consideration. 



The writer in the Archiv mentions, that in one specimen the crystals were 

 outside the shell. I have never known an instance of this nature, and I do not 

 consider it possible for the exterior surface of the Echinus to regulate the size 

 and disposition of the crystals in the same manner as the interior. 



Perhaps the above brief notice may to some of your readers place the matter 

 in a clearer light than the passage of which you have given a translation. 



Your obedient servant, 



Edward Charlesworth. 



Neville Wood, Esq. 



On the Discovery of Cinclidium stygium in Britain. 

 To the Editor of the Naturalist. 



Sir ? — I have this moment seen, for the first time, the number of The Naturalut 

 for May, and am not a little surprised to find myself mentioned in it (p. 101) 

 as having presented to the Botanical Society of London a new plant found on a 

 Moor near " Malkham Farm" Yorkshire, and named by me Cinclidium styrzi- 

 cum. Now it is quite true that I did, some time ago, communicate to the 

 Society, through the medium of the Curator, Mr. Daniel Cooper, a specimen 

 or two of a Moss new to Britain, but it was neither discovered nor named by me. 

 It is the Cinclidium stygium, and has long been known as a native of the North 

 of Europe. I believe it was first described by Swartz in Diario Schrcederi, 

 and subsequently by Wahlenberg in Flora Lapponica, p. 355; it is also 

 figured in the Flora Danica, tab. 1422. 



This very interesting addition to the British Flora was discovered on the 



