79 



Without central nodules. 176 



With a central nodule or with two or more nodules away from the 

 centre. 



In side view appearing as if bent. ACHNANTHE^:. 



In side view, unsymmetrical, with one edge convex, the other nearly 



straight. CYMBELLE.E. 

 Symmetrical in both front and side views. 



In side view rectangular. In front view long, with a nodular infla- 

 tion at each end as well as in the centre. TABELLARIE.E. 



In side view rounded or truncate at the ends. In front view boat 

 shaped ; with a central, longitudinal line ; usually with small, 

 not inflated, terminal nodules. Sometimes in place of the central 

 nodule there is a transverse space free from striae. NAVICULACE^E. 



In side view rectangular. In front view oval or elliptical. 



FRAGILARIE.E. 



176. With longitudinal or marginal keels. 176, b 

 Without keels. 



In front view somewhat crescent shaped. Uninterruptedly ribbed, 

 striated, or dotted. EUNOTIE^:. 



In front view oval, elliptical, or nearly circular. In side view some- 

 times rectangular, sometimes flexuous. With radiating, or inter- 

 rupted, transverse ribs, often with the intervals dotted. 



SURIRELLEJ-:. 



In front view elliptical or oval, sometimes attenuated at the ends. 

 Smooth, ribbed, or interruptedly striated transversely. In side 

 view rectangular, linear. FRAGILARIE.E. 



176, b. In front view oval or elliptical, sometimes contracted at the 

 central part. Edge furnished with a keel. Transversely striated 

 or ribbed. SURIRELLK i . 



Not transversely striated. With one to three longitudinal keels or 

 ribs. Cylindrical or spindel form. AMPHIPLEURE.*:. 



Transversely ribbed. Ribs very short, or not continuous. Keel 

 usually nearer one margin than the other. Pointed at the ends 

 in one view and generally in both. NITZSCIIIEJE. 



