is called the pseudoraphe and may be present in one or both valves. 

 In some forms there are cross partitions or longitudinal partitions 

 called septa. 



To identify Diatoms it is usually necessary to observe empty 

 frustules or cleared cells. The wall markings, costae and puncta, 

 the septa and the raphe must be discerned. A number of genera 

 may be identified in the living or 'filled' condition, but it is ad- 

 visable to follow a technique for clearing the frustule so that tax- 

 onomic characters become apparent. Special terms are used to 

 describe and differentiate Diatom genera and species. Some of 

 these appear in the following simple glossary. 



Diatoms are found in a variety of habitats, both acid and basic 

 waters; on and in soil. Although some genera occur commonly in 

 acid habitats, the majority are found in basic water and often occur 

 in profusion with blue-green algae. They are macroscopically 

 visible as brownish films on submerged objects, sand, and leaves 

 of aquatic plants. Whereas most genera occur as solitary cells, 

 many are filamentous and some are arranged in tufts and in at- 

 tached, gelatinous colonies. (See reference, p. 660). 



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