Figure 1. Nitsschia dissipata (arrow), the most common diatom species at the 

 confluence of the Yellowstone and Bighorn Rivers in early April 

 1973. (1000X) 



I 



k.-» 



o- 





a* 





Figure 2. a. Fragilaria crotonensis , a true planktonic diatom probably derived 

 from Bighorn Lake. b. Cocconeis placentula var. euglypta . c. Ach - 

 nanthes minutissima. (UOOX) 



•13- 



