148 Clarence J. Elmore 



cc. Ovate. 



d. Costae extending to the median line. 



e. Long-oval. 3. S. saxonica. 



ee. Broadly oval. 4. S. striatula. 

 dd. Costae shortened leaving a clear space along the median 

 line. 



e. Costae heavy. 5. S. robusta. 



ee. Costae delicate. 6. 5". elegans. 



bb. Costae marginal, valves sometimes twisted. 7. 6". ovalis. 



AA. Valves twisted into the form of a figure "8." 8. 5. spiralis. 



1. Surirella linearis W. Sm. Brit. Diat., I, p. 31, pi. 8, fig. 58. 



1853- 

 ^ PI. 21, figs. 785-788. 



Oblong or linear, 16-46 /x long, 8-9 /x wide, sometimes somewhat 

 constricted in the middle, apices cuneate ; costae 3-7 in 10 /x, mar- 

 ginal or extending almost to the pseudoraphe. The costae in this 

 species are described as 2-3.5 ""^ ^O/^- ^^"^ otherwise specimens 

 from Nebraska agree with the type. 



Common in tanks, springs, rivers, etc. : Alma, Andrews, Arago. Ashland, 

 Auburn, Benkleman, Blue Springs, Brock, Broken Bow, Brownlee, Cairo, 

 Central City, Columbus, Cook, Crawford, Culbertson, Dismal River, Fair- 

 bury, Gordon Creek, Grand Island, Hackberry Lake, Lincoln, Lodi, Long 

 Pine, Louisville, Mason City. Milford, New Helena, O'Neill, Orleans, 

 Phalaris Lake, Ruby, St. Michael, St. Paul, Salem, Seneca, Stromsburg, 

 Talmage, Tekamah, Thedford, Valentine, Weeping Water, West Point, 

 York. 



Be!videre, Blackpipe, Rosebud, S. Dak. ; Cheyenne, Wyo. ; Chippewa 

 Falls, Wis. ; Blackhand, New Concord, Rio Grande, Rodney, Ohio. 



2. Surirella biseriata Breb. Alg. Falaise, pi. 7. 1838. 

 PI. 21, fig. 789. 



Lanceolate to elliptical, 96-170 /a long, 25-52 ^a wide, apices 

 sometimes slightly rostrate; costae very heavy, 1.75-2 in 10 /^. 

 somewhat radiate; var. elliptica is a form more elliptical and 

 smaller than the type, some specimens only 39 ix long. 



In creeks, etc. : Andrews, Crawford, Oakdale, Tekamah. 



Fossil : Greeley County. 



Little White River, Rosebud, S. Dak. ; Stockton, Cal. 



