150 THE MICROSCOPIST. 



84. Rhizoselenia. Fr. elongate, subcylindrical, marked 

 with transverse or spiral lines, ends oblique or conical, 

 and with one or more terminal bristles ; marine. 



85. Hemiaulus. Fr. single, compressed, rectangular; 

 angles produced into tubular direct processes, those on 

 one valve longer than on the other ; fossil. 



86. Syringidium. Fr. single, terete, acuminate at one 

 end, two-horned at the other ; marine. 



87. Periptera.Fr. single, compressed ; v. unequal, one 

 simply turgid, the other with marginal wings or spines ; 

 fossil. 



88. Didadia. Fr. single; v. unequal, one turgid and 

 simple, the other two-horned ; fossil. 



COHORT 18. ANGULAT^E. Valves angular. 



89. Triceratium. Fr. free ; v. triangular, each angle 

 with a minute tooth or horn ; marine. 



90. Syndendrium. Fr. single, subquadrangular ; v. un- 

 equal, slightly turgid, one smooth, the other with numer- 

 ous median spines, or little horns branched at the ends. 



B. Frustules enveloped in a mass of Gelatin, or contained in 

 Gelatinous Tubes, forming a Frond. 



91. Mastogloia. Frond mammilate ; fr.Jike Navicula, 

 but hoops with loculi ; aquatic and marine. 



92. Dickieia: Frond leaf-like ; fr. like Namcula or 

 Stamoneis ; marine. 



93. Berkeley^. Frond rounded at base, filamentous at 

 circumference ; fr. navicular ; marine. 



94. Homoeocladia. Frond sparingly divided, filiform ; 

 fr. like Nitzschia ; marine. 



95. Colletonema. Frond filamentous, filaments not 

 branched ; fr. like Namcula or Gyrosigma ; aquatic. 



96. Schizonema. Frond filamentous, branched ; fr. like 

 Namcula; marine. 



