TAXONOMY 



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ends of stalks, while others are held in gelatinous masses. Their 

 siliceous skeleta are deposited constantly on the floor of ponds, rivers, 

 lakes and seas, often in such abundance as to form Diatomaceous 

 earths or Kieselguhrs (Siliceous Earths). Huge geological deposits 

 of this material have been found in various parts of the world. The 

 most remarkable for extent as well as for the number and beauty of 

 the species contained in it is that at Richmond, Virginia. It is in 

 many places 25 to 40 feet in depth and extends for many miles. 



PIG. 116. Licmophora flabellata, a diatom with wedge-shaped frustules borne 

 on the ends of stalks, producing a fan-like arrangement. (After Carpenter.} 



Many of the diatomaceous earths are useful as absorbent and polish- 

 ing powders. The United States Pharmacopoeia IX recognizes, 

 under the name of Terra Silicea Purificata (Purified Siliceous Earth), 

 a powder consisting of the frustules and fragments of diatoms which 

 has been purified by boiling with diluted hydrochloric acid, washed 

 and calcined. 



Diatoms exhibit two modes of reproduction, viz., fission and for- 

 mation of an auxospore. The more common method is that of 



