62 Clarence J. Elmore 



extending to the ends of the valves. The form described as var. 

 dansei Thw,, Schonf. I.e., is more nearly represented by figs. 174- 

 175, being more linear with cimeate ends. 



Lakeside, North Platte, Scottsbluff. 



Devils Lake and fresh water near Devils Lake, N. Dak. 



3. Mastigloia grevillei W. Sm. Brit. Diat., II, p. 65, pi. 62, fig. 

 389. 1856. 



PI. 5, figs. 176-177. 



Linear-elliptical, slightly tapering at the ends, 35-60/* long, 

 10-12 ju, wide; striations coarsely granular, radiating, 10-15 ^^ ^O/^' 

 shortened opposite the central nodule, leaving a rounded hyaline 

 space; marginal rows of cells about 8 in 10 jx. 



In pond w^ith Cladophora, Scottsbluff. 



19. Navicula 



Navicula Bory, Diet. Class., XI, p. 4/2. 1826. 



Etym., Lat. diminutive of navis, boat, from the boat-shaped 

 valves. 



Cells single, free or enclosed in gelatinous tubes, or rarely coher- 

 ing in chains ; elliptical to linear-lanceolate in valve view, rectangu- 

 lar and straight in girdle view ; with or without interzones, inter- 

 zonal septa not marginally chambered ; valves bilaterally symmetri- 

 cal with a straight or slightly curved raphe, no keel ; with round 

 central and polar nodules ; surface transversely punctate-striate or 

 ribbed. Auxospore formation : two mother cells lying parallel to 

 each other surround themselves with a gelatinous envelope, cast off 

 the old valves, and the contents of the two unite, forming two 

 auxospores which are surrounded by a siliceous sheath (peri- 

 zonium). 



A. With costae, i.e., heavy ribs. 



h. Costae not composed of rows of dots. i. Pinmilarlae, page 63. 



bb. Striations heavy appearing like costae, but composed of rows of 

 dots. 2. Radio sac, page 71. 



AA. Striations consisting of rows of dots. 



b. Valves with striations interrupted by two sulci near the raphe. 



3. Lyratac. page 81. 

 bb. Valves more or less lanceolate, elliptic, or linear-lanceolate, with- 

 out a sulcus. 



