13 



26a Valves with longitudinal "shadow"-lines or blank 



spaces 27 



26b Valves without longitudinal lines or blank spaces 29 



27a Transverse striae continuous, crossed by one or two 



longitudinal "shadow "-lines paralleling valve margin.... 



Caloneis (p. 63) 



27b Transverse striae discontinuous, interrupted by blank 



spaces or "shadow"-lines 28 



28a Longitudinal "shadow "-lines or blank spaces near valve 



margins; ends of raphe near central nodule usually turned 

 in opposite directions Neidium (p. 6^) 



28b Longitudinal "shadow"-lines or blank spaces scattered, 

 central pores of raphe near central nodule turned if at 

 all in the same direction Anomoeoneis (p. 65) 



29a Valves and raphe s igmoid 30 



29b Valves and raphe not sigmoid 31 



30a Valves with transverse and longitudinal striae 



Gyros igma (p. 67) 



30b Valves with transverse and oblique striae 



Pleurosigma (p. 67) 



31a Frustules with septae Mastogloia (p. 68) 



31b Frustules without septae 32 



32a Raphe enclosed in a siliceous rib Diploneis (p. 68) 



32b Raphe not enclosed in a siliceous rib 33 



33a Valves with chambered striae appearing as heavy costae; 



valves usually with parallel sides and broadly rounded poles. 



Pinnularia (p. 70) 



33b Valves with striae appearing otherwise 3^ 



