166 alg^:. 



85. Chroolepus. Filaments rigid, subsolid, opaque, torulose, 

 falling to powder. 



86. Protonema. Filaments subarticulated, rooting (among 

 mosses.) 



87. Hygrocrocis. Filaments hyaline, interwoven into a 

 uniform membrane or gelatine. 



88. Leptomitus. Filaments hyaline, erect, parasitical. 



Div. IV. Diatomace^. Plants growing in the sea or in 

 fresh tvater, small, and for the most part very minute and para- 

 sitical ; composed of rigid, fragile, more or less transparent cor- 

 puscles (frustula), variously united in parallel series, in circles, 

 or in filaments ; or scattered through a mucous mass; or dis- 

 posed in longitudinal series, through gelatinous branched fronds. 



Tribe XXII. DesmidiEjE. Filaments cylindrical or angular, 

 at length separating into frustula. 



89. Meloseira. Frustula forming simple, pseudo-articu- 

 lated filaments, constricted at the articulation. 



Tribe XXIII. Fragilarieje. Frustula plane, rectilinear, 

 disposed in circles or filaments. 



90. Fragilaria. Frustula forming densely striated, fragile 

 filaments (not cohering at the angles.) 



91. Diatoma. Frustula forming fragile plane filaments, at 

 length separating and cohering at the angles ; or sessile, and 

 arranged in a fasciculate or flabellate manner. 



92. Frustulia. Frustula linear, free or imbedded in a ge- 

 latinous mass. 



Tribe XXIV. Styllarieje. Frustula plane, wedge-shaped, 

 disposed in circles or fans. 



93. Licmophora. Frustula stipitate, flabelliform. 



94. Meridion. Frustula united into circles or segments of 

 circles, sessile. 



Tribe XXV. Cymbelle;e. Frustula elliptical. 



95. Gomphonema. Frustula subgeminate, terminating a 

 very slender, simple or branched filament. 



96. Schizonema. Frustula in longitudinal series, and en- 

 closed in a simple or branched, filiform, mucous, membrana- 

 ceous frond. 



