Protozoa 49 



8 — Cells cuneate in girdle view (i.e. valves not parallel) rachis median, interzones pres- 

 ent 9 



^Cells rectangular in girdle view, or if cuneate the rachis not median, interzones present 

 or absent 10 



9 — ^Valves without transverse ribs, cells not stalked Sceptroneis 



—Valves finely transverse-striate and with transverse ribs (fig. 11) Meridion 



10 — Rachis median, without central eye 11 



— Rachis near one margin 12 



11 — Valves with transverse ribs (figs. 12, 13, 14) ( = Odontidium) Diatoma 



— Valves without transverse ribs. Cells arranged radially (fig. 37) Asterlonella cells in 

 filaments or zig-zag chains, valves flat (fig. 15) Fragilaria; cells single or forming 

 fan like stalked clusters (figs. 21, 22) Synedra 



12 — Ends of valves alike. Pseudoraphe and central nodule evident, Ceratoneis pseudo- 



raphe and central nodule not evident (figs. 6, 7) Eunotia 



— Ends of valves unlike ( = Actlnella) Tibiella 



13 — Rachis containing an elongate slit (raphe) through the cell waU 14 



— Rachis evident as a narrow, unmarked strip or keeled; valve with 2 lateral wing keels, 

 each enclosing a raphe 23 



14 — Rachis commonly median, often more or l6ss lateral, not keeled or when keeled not 



punctate, interzones present or absent 15 



— Rachis lateral, less often median, punctate keeled raphe not plainly visible Keel 

 median, Bacillaria; keel at one edge (figs. 19, 20) (Homoeocladia) Nitzschia 



15 — Valves parallel 16 



— Valves not parallel 21 



16^Rachis of valve not keeled 17 



— Rachis of valve with a keel; keel (including raphe) sigmoid, median Amphiprora 



17 — Raphe almost straight 18 



— Raphe strongly sigmoid. Cell not twisted (fig. 23), Gyrosigma; cell twisted 



Scoliopleura 



18 — Raphe with a simple border 19 



— Raphe bordered by 2 ridges. Central nodule small or only slightly elongated Brebis- 

 sonia; central nodule much elongated, riblike Amphipleura 



19 — Septa of interzones (when present) not fenestrated 20 



— Septa of interzones fenestrated. Both valves with a raphe, Mastogloia; only one 

 valve with a raphe Cocconeis 



20 — Cells straight in girdle view. Including the subgenera Stauroneis (fig. 16), Frustulia 



(fig. 18), and Pinnularia (fig. 34). (Figs. 24, 25, 26, 27) . . _. . .Navicula 



— Cells curved. Both valves with a raphe, Rhoiconeis; only one valve with a raphe, 

 Achnanthes including Achnanthldium (figs. 39, 40). 



21 — Ends of valves approximating. Cells straight in girdle view (figs. 20, 30) Gompho- 



nema ; ceUs curved in girdle view Rhoicosphenia 



— Edges of valves approximating 22 



22 — Valves without transverse ribs. Girdle narrow, not striate (fig. 2>Z), Cymbella; girdle 



broad, striate (fig. 41) Amphora 



— Valves with transverse ribs, raphe not evident. (Fig. 35). . (Cystopleura) Epithemia 



23 — Valve surface undulate ( = Cymatopleura) Sphinctocystis 



— Valve surface not undulate. Valve cuneate, reniform, elliptical or linear (fig. ^ 38), 

 Surirella; valves subcircular, saddle shaped (figs. 31, 32) Campylodiscus 



PROTOZOA 



1 — Animals with tentacles, and when adult usually attached by a stalk. . . .SUCTORIA 

 — Animals with speudopods, flagella or ciha 2 



2 — Animals with pseudopods 3 



— Animals with cilia or flagella 4 



