282 



" The spines are not sulphate of lime, but 1 consider them to be 

 silica ; for after much boiling in silver vessels, although they scarcely 

 seemed afPected by caustic alkali, yet, when heated to redness, they 

 fused and lošt all traces of regular form, and the whole of the fused 

 mass, small as it was, became entirely soluble in water. When mu- 

 riatic acid was added, the silica vpas precipitated with the usual gela- 

 tinous and flocculent appearances ; the only chance is that alumina 

 may possibly be present. I tried one of the blowpipe tests for alu- 

 mina, and there seemed to be the appearance of this substance ; but 

 I think the tęst is subject to fallacy. So I conclude that the sub- 

 stance is silica only ; the water — does it proceed from cells, or is it 

 held accidentally ? 



" I shall be curious to know the history, which I believe you pro- 

 mised after my reportiug upon their composition, and of course wish 

 to know how far you consider this examination corresponds to the 

 impression on your own mind ; for I think you told me that more 

 than one chemist had given an opinion, which possibly may differ 

 from mine. 



" Believe me to be, 



" Respectfully and sincerely, 



"Thomas John Pearsall." 



The sponge to which it is attached has no real connection with 

 the coral, except as affording it the means of support, and is of the 

 common structure. 



Some fibres of the axis of this coral were in the coUection of Sir 

 Hans Sloane, and it was doubtful to which kingdom these isolated 

 siliceous threads could belong, until the arrival in this country of the 

 specimen, which was sent from Canton by Mr. Reeves, under the 

 name of Glass plant, described by me in the paper above referred to. 



There can be no doubt, after the examination of the two speci- 

 mens in the British Museum, one in my own collection, one in Paris, 

 and several iu the Leyden Museum, that the bark evidently belongs 

 to the axis, and that this coral is a true zoophyte, and not a sponge 

 covered with a parasitic zoophyte, as it is regarded by M. Valen- 

 ciennes. See Milne-Edwards, British Fossil Corals, 81. 



Suborder II. Lithophyta. 



Axis calcareous, continued or jointed, effervescing with muriatic 

 acid. 



In the genus Subergorgia the axis is cork-like ; in the other 

 genera it is ligneous, more stony and hard at the base ; in others 

 it is entirely stony and hard, and usually of a white colour ; but in 

 Coralliutn it is generally deep bright red, but sometimes pink or 

 white. In general it is solid, and formed of concentric laminae. In 

 Melifcea and Solanderia (?) it is cavernous, pierced with cylindrical 

 tortuous canals. 



