The Diatoms of Nebraska 137 



Fossil : Mullen. 



Belvidere, Rapid City, Rosebud. S. Dak. ; Devils Lake, N. Dak. ; Stock- 

 ton, Cal. ; New Concord, Ohio ; Emporia, Kansas. 



5. SiGMATA 



A. Keel with coarse projecting dots. 11. H. fasciculata. 



AA. Keel with rather delicate dots. \2. H. sigma. 



11. Homoeocladia fasciculata (Grim.) Kuntze. Rez>. Gen. Plant., 



Ill, p. 409. i8p8. 



Nitsschia fasciculata Grim. Alg. Kasp. Mcer, p. iig. iSyS. 



PI. 19, fig. 717. 



More or less sigmoid, 67-95 /^ lorig, 6-7 /i. wide ; keel excentric 

 with 4-6 dots in 10 /a, dots somewhat elongated; striations 28-30 

 in 10 /a; girdle face sigmoid. 



Pleasant Dale. 



12. Homoeocladia sigma (Kiitz.) Kuntze. Rev. Gen. Plant., Ill, 



p. 40Q. 1898. 



Nitsschia sigma (Kiitz.) W. Sm. Brit. Diat., I, p. 59. 18 j^. 



Synedra sigma Kiitz. BacilL, p. 6/, pi. 50, fig. 14. 1844. 



PI. 19, figs. 718-724. 



Linear, slightly sigmoid, 88-250 /x long, 5-11 fx wide; keel some- 

 what excentric with 7-9 dots in 10 /a; striations 22-30 in 10 /x,; 

 girdle face sigmoid with tapering apices. Variable and presenting 

 many forms represented by var. rigidula, figs. '/22-'j22, ; var. rigida, 

 fig. 721. Very much sigmoid in var. interccdens, fig. 720. 



In creeks, springs, ponds, etc., with Spirogyra and other algae : Ashland, 

 Auburn, Dunning, Emerald, Fairbury, Grand Island, Hyannis, Julian, Lin- 

 coln, Milford, North Platte, Oakdale, Orella, Sheridan County, Stanton, 

 Stromsburg, Tekamah, Trenton, Valentine. Wahoo. 



Belvidere, Cutmeat, S. Dak. ; Stockton, Cal. 



6. Obtusae 



13. Homoeocladia arcus (Buhln.) Kuntze. Rev. Gen. Plant., Ill, 



p. 409. 1898. 

 Nitzschia arcus Buhln. in Hcdzvigia, II, p. 22, pi. 2, fig. t. 18 ^^9. 

 Nitzschia obfusa W. Sm. Brit. Diat., I, p. ^9, pi. /?, fig. 109. 



1853- 

 PI. 23, fig. 861. 



