102 Clarence J. Elmore 



times one or both margins bent in at the ends, abnormal forms 

 also occurring; upper surface arched, upper valve with narrow 

 pseudoraphe, lower valve with fine but distinct raphe, distinct 

 terminal and central nodules ; striations of the upper valve finely 

 granular, on the margin in the middle often united in twos, slightly 

 radiate, granules of the striations irregular, giving with oblique 

 illumination an undulating appearance; lower valve with narrow 

 area along the raphe, somewhat wider at the central nodule ; stri- 

 ations extending almost to the margins of the valve, leaving onl}' a 

 narrow structureless marginal ring; length 15-30^, breadth 10- 

 20 IX, striations 17-18 in 10 /a. 



C. placentula var. lineata Ehr., Amer., p. 81, is larger and with 

 striations on the upper valve forming zigzag longitudinal lines. 

 Fig. 506, Valentine, Dewey Lake. 



Epiphytic on filamentous algae, very common: Andrews, Ashland, Ben- 

 kleman. Broken Bow, Burge, Central City, Cody Lake, Columbus, Culbert- 

 son, Dewey Lake, Dismal River, Dunning, Fairbury, Fremont, Grand 

 Island, Hackberry Lake, Halsey, Hyannis, Lakeside, Lodi, Long Pine, 

 Louisville, Norfolk, North Platte, Northport, Orleans, Pelican Lake, Ruby, 

 Rupert, St. Paul, Seneca, Stanton, Tioga, Trenton, Valentine, West Point, 

 Wann, Woodlake. 



Fossil : Agate, Cherry County, Greeley County, Hay Springs, Thedford. 



Cheyenne, Wyo. ; Court Lake, Devils Lake, and fresh water near Devils 

 Lake, N. Dak. ; Belvidere, Blackpipe, Little White River, Norris, Rapid 

 City, S. Dak. ; Muskingum River, pond on island in Lake Erie, Ohio. 



3. Cocconeis disculus (Schum.) CI. in CI. & Jentssch Alhiv. Diat. 

 Norddciitsch., p. I2p. 1882. 

 Navicida discuhts Schum. Preuss. Diat., p. 21, pi. 2, fig. i*j. 



1864. 

 PI. 13,%. 508. 



Broadly elliptical, 11-20 /a long, 9-15 /tt wide; striations 8-13 in 

 10 /x, composed of coarse dots, shortened, leaving a lanceolate 

 hyaline space ; lower valve with very delicate, scarcely visible 

 raphe ; striations radiate, consisting of 3 or 4 heavy elongated dots. 



In Loup River near Lodi. 



