The Diatoms of Nebraska 151 



Cells solitary, free, disk-shaped, disk twisted or saddle-shaped ; 

 valves round-elliptic with short, mostly radiate ribs and a margin^ 

 keel concealing the raphe ; pseudoraphe median, but at right angles 

 in the two valves. Chromatophores as in Sphinctocystis. 



A. Central space with coarse dots. 



h. Valves bent. i. C. clypcus. 



bb. Valves very much bent. 2. C. hibcrnicus. 



AA. Dots lacking in the central space which is somewhat rectangular. 



3. C. bicostatus. 



1. Campylodiscus clypeus Ehr. AbJi., p. 201. 1840. 

 PI. 21, fig. 808. 



Nearly circular. 85-200 /a in diameter, saddle-shaped; costae 

 reaching about half way to the center, about 1.5 in 10 /a; striations 

 among the costae, 20-21 in 10 /a. consisting of elongated dots; 

 central portion of the valve filled with coarse dots irregularly or 

 radially arranged. 



Typically a marine species : Big Alkali Lake ; pool by lake, Lakeside. 

 Devils Lake, N. Dak. 



2. Campylodiscus hibernicus Ehr. Bcr. Bed. Akod., p. 1^4. 



1845. 



PI. 21, fig. 809. 



Nearly circular, 90-100 /a in diameter, very much bent; costae 

 1.5-2 in 10 /x, very heavy near the margin, tapering toward the 

 center, where they leave a nearly square punctate space. 



In Rapid Creek at Rapid City, S. Dak. 



3. Campylodiscus bicostatus ^^^ Sm. Brit. Diaf., II, p. 88. 



1836. 



PI. 21, fig. 810. 



Nearly circular, 30-50 /x in diameter, with narrow costae the 

 spaces between which are jnmctate ; central space somewhat rec- 

 tangular with rounded angles, the center of which has no dots. 



With Cladophora in creek : Cheyenne, Wyo. 



