The Diatoms of Nebraska 87 



Elliptic with apices sometimes tapering, obtuse, 57-1 14^0, long, 

 21-36 /A wide (one specimen was only 33 ju, long) ; striations punc- 

 tate, 12-16 in JO fx, radiate, interrupted by a longitudinal sulcus, 

 leaving a single row of puncta next to the raphe, the puncta closer 

 near the margin of the valves ; also interrupted by a transverse 

 sulcus forming a pseudostauros which usually extends much nearer 

 one margin of the valve than the other. The typical specimens of 

 this species have rostrate apices, but many are regularly elliptic. 

 These elliptic forms seem to belong to N. polygramma, a species 

 which Cleve, Naz'. Diat., II, p. 6, states is a form of A'', sculpta 

 (rostrata). Many of the specimens from Devils Lake have the 

 regularly rhomboidal form shown in fig. 392. 



In fresh or brackish water, usually where diatom conditions are good, 

 also fossil : Anselmo, Big Alkali Lake, Clear Lake, Dismal River, Hack- 

 berry Lake, Halse3% Lakeside, Little Alkali Lake, North Platte, Orella, 

 St. Paul, Sheridan County, Snake River, Thedford, Valentine, Whitman. 



Fossil : Greeley County, Hay Springs, Loup City, Mullen, Spalding, 

 Thedford. 



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



53. Navicula sphaerophora Kiitz. Bacill., p. 95, pi. 4, fig. 77. 



1844. 



PI. II, figs. 398-400. 



Elliptic- or oblong-lanceolate with rostrate-capitate apices, 32- 

 55 /A long, 10-20 /x wide; striations radiate, punctate, interrupted 

 by a longitudinal sulcus which is narrower than in N. rostrata, and 

 by a transverse sulcus that forms a pseudostauros, about 16 in 10 ;u.. 

 Differs from N. rostrata in its narrower longitudinal sulcus, capi- 

 tate apices, and usually smaller size. 



In creeks, rivers, etc., usually with other algae, also fossil : Arago, Brock, 

 Broken Bow, Brownlee, Cherry County, Clear Lake, Dismal River, Dun- 

 bar, Fremont, Grand Island, Hackberry Lake, Halsey, Humboldt, Julian, 

 Long Pine, New Helena, Peru, Phalaris Lake, Ruby, St. Paul, Salem, 

 Seneca, Sheridan County, Talmage, Valentine, Whitman. 



Fossil : Greeley County, Loup City, Mullen, Thedford. 



Blackpipe, Rosebud, S. Dak. 



9. Serianteae 



54. Navicula serians (Breb.) Kiitz. Bacill., p. pj>, pi. 50, fig. 2j; 



pi. 28, fig. 4^. 1844. 

 Frustulia serians Breb. ex spec. 



