Keel - a ridge projecting from the valve -surface, enclosing the "canal" 



raphe, usually not medial on the valve (see Nitzschia , p. 89) 

 Linear - long and nearly uniform in width. 

 Micron - 0.001 millimeter. 

 Multiseriate - having more than one row of punctae (see Stephanodiscus 



astrea , p. 28) 

 Nodule - internal thickening of the cell wall in the central area or 



terminal portions (poles) of the valves of pennate diatoms. 

 Ocellus - a raised, rounded or ovate thickening of the valve surface 



having the appearance of a large pore (see Cyclotella ocellata , 



P- 27) 



Poles - extreme ends of the valves of pennate diatoms. 



Pseudoraphe - a smooth, linear space between the medial ends of the 



striae or costae on the valves of pennate diatoms. A term applied 



only to valves without a true raphe (see Synedra ulna, p. k-5) 

 Punctae - small holes (pores) or thin, circular, sieve-like areas in the 



frustule . 

 Raphe - a fissure or slit in the valve face which may be along or eccentric 



to the medial axis of the valve; when located in a keel or wing it is 



referred to as a "canal" raphe. 

 Rhomboid - a parallelogram in which the angles are oblique and the adjacent 



sides are unequal (see Nitzschia , p. 89) 

 Septae - internal partitions or cross walls, usually appearing as dark 



lines (see Tabellaria fenestra ta , p. 32) 

 Shadow-lines - dark "diffraction" lines which appear in the frustule wherever 



abrupt changes in thickness of the valve face occur (see Caloneis, p. 63) 



