The Diatoms of Nebraska 89 



rounded; striations transverse or slightly radiate, 15-18 in 10 /u,, 

 lacking in the center, forming a pseudostauros. Var. niinuta is 

 probably only a small form of the same. 



Among other diatoms, more often in ditches, muddy pools, etc. : 

 Andrews, Brownlee, Callaway, Crete, Dunning, Fremont, Grand Island, 

 Lakeside, Louisville, North Platte, Orella, Pleasant Dale, St. Paul, Scotts- 

 bluff, Seneca, Wann, West Point. 



Fossil : Loup City. 



Cutmeat, Turtle River, S. Dak. ; Sully's Hill, N. Dak. ; Chippewa Falls, 

 Wis. 



58. Navicula silicula Ehr. Amer., p. i^i. 1843. 

 Navicula limosa Kiitz. BacilL, p. loi, pi. j, fig. jo. 1844. 

 PI. II, figs. 419-425- 



Linear with three slight inflations, 15-85 /i, long, 7-14 /x wide, 

 apices obtuse, often somewhat apiculate ; striations slightly radiate 

 or nearly transverse, interrupted by a narrow sulcus parallel to the 

 margins, not reaching to the raphe and often leaving a hyaline 

 space along it one-third the width of the valve, more shortened 

 opposite the central nodule, leaving a lanceolate or rounded space. 

 Var. gibberula (figs. 424-425) is a form with larger inflations and 

 closely connected with A'^. trinodis. Dried valves sometimes iri- 

 descent. 



In ditches, etc., also fossil : Andrews, Ashland, Benkleman, Brownlee, 

 Central City, Cody Lake, Crawford, Culbertson, Dismal River, Fremont, 

 Gordon Creek, Grand Island, Halsey, Holt County, Lakeside, Lodi, Louis- 

 ville, Mason City, Norfolk. North Platte, O'Neill, Orella, Pleasant Dale. 

 Polk, Rupert, Ruby, Scottsbluflf, Snake River, Stanton, Talmage, Tekamah. 

 Thedford, Trenton, Valentine, Wann, West Point. 



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



Blackpipe, Corn Creek, Rapid City, Redleaf, Rosebud, Turtle River, 

 S. Dak. ; fresh water near Devils Lake, N. Dak. ; Cheyenne, Wyo. 



59. Navicula trinodis Lewis. Proceed. Acad. A^af. Sci., Phil., p. 



66, pi. II, fig. 6. 1861. 



PI. II, figs. 426-428. 



Linear with two constrictions making a median and two terminal 

 inflations, 22-57 /a loi^g. 7^15/* wide, median inflation as wide as 

 the terminal or wider, apices from broadly roimded to cuneate or 

 attenuate ; striations nearly parallel, tending to be perpendicular to 



