30 



88. Odontella: 



(polymorpha). 



Frustula tabellata, basi stipitata, 

 isthmis (x. x.) concatenata, septis 

 internis loculosa , angulis proces- 

 sibus instructa. 



89. Lithodesmium : 

 (undulatum). 



Frustula in fascias conjuncta (b), fronte (a) triangularia. 

 90. Zygoceras: (Rhombus). 

 i, 



Frustula libera , non concatenata , compressa , fronte (b) naviculacea, 

 latere (a) cingulo medio instructa. 



