142 THE MICROSCOPIST. 



hundred characteristic forms, is a valuable assistance. 

 The following table, from the Micrographic Dictionary, 

 gives an analysis of tribes and genera : Fr. denotes the 

 frustules in front view; v. the valves; granular striae 

 means striae resolvable into dots ; and continuous striae 

 signify costae or caualiculse. 



A. Frustules not contained in a Gelatinous Mass or Tube. 



TRIBE I. STRIAE. Frustules usually transversely stri- 

 ate, but neither vittate nor areolate. 



f Valves without a Median Nodule. 



COHORT 1. EUNOTIEJE. Fr. arcuate, single, or united 

 into a straight filament. 



1. Epithemia. Fr. single or binate, with transverse or 

 slightly radiant striae, some continuous ; no terminal nod- 

 ules; aquatic and marine. 



2. Eunotia* Fr. single or binate; v. with slightly ra- 

 diant granular striae and terminal nodules; aquatic. 



3. -Himantidium. Fr. as in Eunotia, but united into a 

 filament; striae parallel, transverse; aquatic. 



COHORT 2. MERIDE.E. Fr. cuneate, single, or united 

 into a curved or spinal band; v. with continuous or gran- 

 ular striae. 



4. Meridion. Fr. cuneate, united into a spiral band; 

 striae continuous ; aquatic. 



5. Eucampia. Fr. united into an arched band ; v. punc- 

 tate; marine. 



6. Oncosphenia. Fr. single, cuneate, uncinate at the 

 narrow end; striae granular; aquatic. 



COHORT 3. FRAGILLARIEJE. Fr. quadrilateral, single, or 

 united into a filament or chain; v. with continuous or 

 granular striae. 



7. Diatom a. Fr. linear or rectangular, united by the 



