M,G2E. 



263 



99. Desmidium. Frustula forming simple angular pseudo- 

 articulated filaments, hyaline at the eremite angles, at length se- 

 parating-. 



Tribe XXIII. Fkagilaiuk.e. Filaments plane, extremelg 

 fragile, composed of rectilinear fr ust ula; ( frustula sometimes ap- 

 parently radiating from a centre and not presenting the appear- 

 ance of a Ji lament. ) 



100. FftAGILARIA. Frustula forming plane, p^eudo-artien- 

 lated, densely striated, fragile filaments, separating at the stria- 

 (not cohering at their angles). 



101. Achnanthes. Frond stipitate, standard-shaped, coin- 

 posed o£ few frustula, which at length separate (without coher- 

 ing at their angles). 



102. Diatoma. Frustula forming pseudo-articulated, plane 

 filaments, at length separating and cohering at their angles. 



103. Frlstllia. Frustula linear, free or imbedded in a 

 shapeless mass, solitary or binate. 



TRIBE XXIV. Styllakik.i:. Frustula plane, wedge-shaped. 



104. STYLLABIA. Frustula wedge-shaped, separate, stem- 

 less, not united into plane lamina'. 



105. LlCMOPHORA. Frustula wedge-shaped, flabelliform, 

 stipitate. 



106. Mebj'dion. Frustula wedge-shaped, in plane sessile 

 circles <>r segments of circles. 



Tribe XXV. Cymbellrs. Frustula elliptical, 



107. Gomphonema. Frustula subgeminate, terminating a 

 vt-iy Blender, Bimple or branched filament 



108. HoM<BO< LABIA. FrttStula arranged in numerous, bi- 

 nate, distant, parallel series, within a tubular from/. Ag. 



109. Bebjklbya. Frustula in longitudinal series, within 

 simple mucous filaments, which are free at the extremity, but 

 united below into a roundish gelatinous ma—. 



1 10. Mn romeoa. Frustula arranged in longitudinal series, 

 within a cartilaginous or gelatinous frona\ Ag. 



111. Si hizonema. Frustula in longitudinal series and in- 

 closed in r simple or branched, filiform, mucous, memhrtaaceous 



frond. 



112. Cymbslla. Frustula elliptical, binate, free, or imbed- 

 ded in a mucous mass. 



