C2 Clarence J. Elmore 



River, Dunning, Durly Lake, Grand Island, Hackberry Lake, Hastings, 

 Ithaca, Johnson, Lakeside, Long Pine, Milford, North Platte, Pelican Lake, 

 Plattsmouth, Ruby, Seneca, St. Michael, Stromsburg, Talmage, Thedford, 

 Valentine, West Point, Whitman. 



Fossil: Cherry County, Loup City, Williams's Canyon. 



Cutmeat, Dallas, Kadoka, Rapid City, Turtle River, S. Dak.; Devils 

 Lake, N. Dak.; Stockton, Cal. ; Put-in Bay, Ohio. 



3. Fragilaria construens (Ehr.) Grun. in Wien. Verh., p. S/i- 



1862. 



Staurosira construens Ehr. Abh., p. 424. 1841. 



PI. 2. figs. 73-84; pi. 22, fig. 816. 



Very variable, from oval to cruciform, or sometimes contracted 

 in the middle, ii-i6;a long; rachis lanceolate, striations 10-18 in 

 10 /a; cells tmited in short filaments. Var. venter and var. binodis 

 have been described, but they are probably mere forms. 



Very common in creeks, rivers, ponds, etc., especially where the water 

 is quiet and conditions for algae are good, also fossil : Andrews, Burge, 

 Clear Lake, Crawford, Culbertson, Dewey Lake, Dismal River, Dunning. 

 Gordon Creek, Grand Island, Halsey, Ithaca, Long Pine, Melia, New 

 Helena, Niobrara River, Norfolk, North Platte, Oakdale, O'Neill, Red 

 Cloud, Seneca, Thedford, Valentine, West Point. 



Fossil: Agate, Cherry County, Hay Springs, Greeley County, Loup City, 

 Merriman, Mullen, Spalding, Thedford, Wheeler County, Williams's Can- 

 yon. 



Turtle River and Rosebud, S. Dak. 



4. Fragilaria mutabilis (W. Sm.) Grun. Ocst. Diat., p. $69. 



1882. 

 Odontidmm niutabile W. Sm. Brit. Diat., II, p. IJ, pi. S4, fiO- 



2po. i8j6. 

 PI. 2, fig. 85 ; pi. 22, fig. 817. 



Cells from almost circular to oval, elliptical, or linear-acuminate, 

 5-25 ;a long; striations distinct, not resolvable into beads, 7-10 

 in lO/x. 



St. Paul, Seneca, Snake Creek. 



Fossil : Cherry County, Mullen, Wheeler County. 



Blackpipe, S. Dak. 



