









Gomphonema ottvaceum 



Figure 2. GompJionema olivaceum. The illustration at the bottom represents several 

 soft thalli attached to and completely covering a rock. The mottled dark area represents 

 bare rock at a point where an algal thallus has been cut away. The upper drawings represent 

 successive magnifications of the area cut away. Insect larvae which feed on these diatoms are 

 shown within the algal mass. 



^i-M^^ji'.^^ -^-x 



l^ivularici sp 



Figure 3. Rivularia sp. Stippled portion represents a rock to which several subspherical 

 colonies of Rivularia are attached. The upper drawings show increasing magnification of a 

 single colony or thallus. Calcium carbonate cr)stals are shown as they appear in the gelatin 

 between adjacent algal filaments. 



357 



