Tlie Diatoms of Nebraska 85 



Belvidere, Interior, Little White River, Norris, Rosebud, S. Dak. ; Court 

 Lake, Devils Lake, fresh water near Devils Lake, N. Dak. ; Stockton, Cal. ; 

 Ft. Collins, Colo. 



50. Navicula mucronata n. sp. 



PI. 10, %. 387. 



Rectangtilar, 40-50 /^ long, 14-16 ^u, wide, apices abruptly 

 pointed ; striations nearly perpendictilar to the raphe, shghtly radi- 

 ate, about 15 in 10 fx, extending nearly to the raphe, leaving a 

 narrow space which is shghtly enlarged opposite the central 

 nodule. 



In roadside ditch and in Wood River at Grand Island, and in Cody Lake 

 in Cherry County. 



51. Navicula ambigua Ehr. Verb., p. i2g, pi. 2, fig. 9. 184^. 

 PI. 10, figs. 374-377, 381, 383-386, 388. 



Like N. fulva, but ustially smaller and with rostrate-capitate 

 apices. Van Heurck, Diat., p. 214, states that A^. ambigua is 

 probably only a variety of A^ fulva (cuspidata), but gives it a 

 place as a species. But Schonfeldt, Diat. Ocst. und Seine, p. /6, 

 makes it only a variety. The two forms occur together with 

 all gradations between them, making it appear as if they were 

 only forms of the same species. But the resting condition de- 

 scribed for A^. fnlva occurs also in A^. ambigua. This condition, 

 as far as observed, occurs only in the typical forms of the two 

 species and never in any of the intermediate forms except possibly 

 in the form represented in fig. 382, and this would indicate that 

 the two species are distinct, for a sporangial condition wotikl not 

 be likely to be found in any but mature forms. 



Common in creeks, ponds, tanks, etc. : Alma, Andrews, Anselmo, Ash- 

 land, Bellevue, Brock, Broken Bow, Brownville, Central City, Clear Lake, 

 Cody Lake, Columbus, Crawford, Crete, Culbertson, Dismal River, Dun- 

 ning, Fremont, Gordon Creek, Grand Island, Hackberry Lake, Haigler, 

 Halsey, Hemingford, Holbrook, Humboldt, Johnson, Lakeside, Lincoln, 

 Little Alkali Lake, Louisville, Nebraska City, New Helena, Norfolk, 

 North Platte, Oakdale, Omaha, O'Neill, Orella, Peru, Pleasant Dale, Red 

 Cloud, Rupert, Ruby, St. Michael, St. Paul, Scottsbluff. Seneca, Seward, 

 Sheridan County, Snake River, Stanton, Stromsburg, Talmage, Tecumseh, 

 Tioga, Trenton, Valentine, Wahoo, Wann, Weeping Water, West Point, 

 Whitman. 



