90 Clarence J. Elmore 



the margins, about i8 in io/a, not reaching to the raphe, leaving a 

 hyahne space along the raphe considerably wider, and rounded 

 opposite the central nodule. Dried specimens usually brownish. 



In same locations as A'', silicula: Alma, Andrews, Arago, Ashland, 

 Auburn, Columbus, Crawford, Crete, Culbertson, Dismal River, Fremont, 

 Gordon Creek, Grand Island, Halsey, Hyannis, Lincoln, Louisville, Mil- 

 ford, North Platte, Oakdale, Pleasant Dale, Rupert, St. Paul, Scottsbluff, 

 Seneca, Stanton, Talmage, Thedford, Trenton, Valentine, Wann, Weeping 

 Water, Whitman, Woodlawn. 



Fossil : Loup City, Mullen. 



Belvidere, Blackpipe, Corn Creek, Rapid City, Rosebud, S. Dak. ; Chey- 

 enne, Wyo. ; Ft. Collins, Colo. ; Rio Grande, Ohio ; Emporia, Kansas. 



12. Affines 



Van Heurck, Syn., p. 221, places all of these forms under A', iridis. 

 Cleve, Syn. Nav. Diat., I, p. 67, states that all of these forms may be 

 varieties of one species. Since there is no definite information as to the 

 life history of the various forms, it seems best in the present work to 

 retain the species as described. 



A. Elongated, 3-6 times as long as wide. 

 b. Margins parallel. 



c. Ends rounded. 60. N. hisulcata. 



cc. Ends cuneate. 61. A^. aiuphigomphus. 



ccc. Ends rostrate. 62. A'', affiiiis. 



bb. Margins convex, ends rounded or sub-rostrate. • 



63. A", iridis. 



bbb. Margins undulating. 62. A", affinis. 



AA. Two to three times as long as broad. 64. A'', dubia. 



60. Navicula bisulcata Lagerst. Spctz. Dial., p. si, pi. L fig. 8. 



1873- 



PI. 12, fig. 429. 



Linear, 40-70 /i, long, 8-12 /x wide, apices rounded ; raphe straight, 

 the central ends bent in opposite directions ; striations punctate, 

 oblique, about 16 in 10 jx, interrupted near the margin of the valve 

 by a deep sulcus, shortened opposite the central nodule, leaving a 

 transversely elongated hyaline space. Dried valves usually brown. 



In creeks, etc.: Andrews, Dunning, St. Paul, Thedford. 

 Fossil : Agate, Greeley County, Spalding. 



