The Diatoms of Nebraska 71 



times faint; apices capitate, 30-80 /x long, 10-16 /x wide; striations 

 radiate in the center, converging at the ends, shortened, leaving a 

 hyaline space along the raphe about one-third the width of the 

 valve, 9-12 in 10 ju. 



In springs, creeks, pools: Auburn, Brock, Broken Bow, Dismal River, 

 Emerald, Grand Island, Hackberry Lake, Long Pine, Valentine, West 

 Point. 



Fossil : Agate, Cherry County, Loup City, Mullen. 



Turtle River, Rosebud, S. Dak. ; Cheyenne, Wyo. 



18. Navicula nodosa Ehr. Inf., p. lyp, pi. XIII, fig. p(f). 1838. 

 PI. 22, fig. 842. 



Valves linear, from strongly tritindulate and capitate to nearly 

 straight and rostrate, SS~95 1^ ^'^^^S' 9~^~ f^ wide; raphe fine, citrved 

 at the ends; striations 8-10 in lO/t, slightly radiate at the center 

 and converging at the ends, shortened, extending only a little more 

 than one-fourth of the width of the valve, lacking opposite the 

 central nodule. 



In creek, New Helena. 



19. Navicula acrosphaeria (Breb.) Kiitz. Bacill., p. p/, pi. 5, 



fig. II. 1844. 



Frustidia acrospJtaena Breb. Consp. Diat., p. ip. 1838. 



PI. 8, fig. 279. 



Linear, more or less gibbous in the middle, or straight and 

 slightly swollen or constricted at the ends, 18-32 /x long, 7-20 ja 

 wide ; costae radiate near the middle and converging at the ends, 

 lacking in the middle, forming a pseudostauros, 9-14 in 10 /x, 

 shortened, leaving an axial area about one-third the width of the 

 valve or extending nearly to the raphe, axial area granular. 



Crawford : in pond, Orella. 



II. Radiosae 



A. Middle striations radiate, terminal converging. 

 b. Striations fine. 



c. Terminal striations in broken lines. 20. A^. oblonga. 

 cc. Striations in continuous lines. 



d. Middle striations alternately long and short. 

 e. Broadly lanceolate. 



/. Not rostrate-capitate. 



