32 Clarence J. Elmore 



g. Terminal nodules near the ends, raphe more 

 or less curved. 



30. CymhcUa, page 115. 

 gg. Terminal nodules usually distant from the 

 ends, raphe straight. 



31. Encyoncma, page 122. 

 ff. Raphe and central nodule close to the ventral 

 margin. 



2>2. Amphora, page 124. 

 ce. Valves with transverse ribs ; raphe not evident. 



2,2,- Cystopleura, page 125. 

 cc. Cells usually elongated ; rachis usually on the margin of the 

 valve, so that striations are not interrupted by it; valves 

 with a dotted keel (Fam. Bacillariaceae). 



34. Homococladia, page 130. 

 ccc. Cells usually oval or elliptical, seldom elongated ; with two 

 wings (Fam. SurircUaceae). 

 d. Valve surface undulate. 35. Sphinctocystis, page 145. 



dd. Valve surface not undulate. 



c. Valves cuneate, reniform, elliptical, or linear. 



2>6. Surirclla, page 147. 

 ee. Valves nearly circular, bent into saddle shape. 



2,7. Campylodiscus, page 150. 



Class Bacillarioideae 

 One-celled aquatic plants living in filaments, or more commonly 

 broken into single cells ; free, attached to the substratum, epiphytic 

 on other plants, or enclosed in gelatinous tubes ; cell wall of cellu- 

 lose infiltrated with silica; the wall of each cell (frustule) consist- 

 ing of two plates (valves) which form the ends of the cell and are 

 connected by two or more girdles, the one fitting outside the other 

 like the cover of a box. Protoplasm parietal and forming a large 

 mass in the center of the cell in which the nucleus is located and 

 which separates the central vacuole into two parts. Chromato- 

 phores plate-like or granular ; chlorophyll obscured by a brownish 

 coloring matter, phycoxanthin. In the elongated, free-swimming 

 families, Naviculaccae, Bacillariaceae, and Surirellaccac, there is a 

 longitudinal slit (raphe) which in Naviculaccae is median, or nearly 

 so, and in the other families is lateral. Propagation by cell divi- 

 sion in which each daughter cell retains one of the valves of the 

 mother cell. Reproduction by the sexual or asexual formation of 

 auxospores. 



