ii8 Clarence J. Elmore 



convex, more or less gibbous, 20-56 /a long, 8-12 /a wide; ends 

 obtuse, slightly attenuate ; raphe curved toward the dorsal margin ; 

 striations nearly perpendicular to the margins, finely granular, 8-1 1 

 in 10 ;a in the middle on the dorsal side, closer elsewhere, extending 

 nearly to the raphe, leavmg a narrow space which is not wider 

 opposite the central nodule, or only slightly so. Van Heurck's 

 figure of C. Icptoccras var. clongata, Diat., pi. i, fig. SS, closely 

 resembles the form found here. 



On muddy banks : Benkleman, Mason City. 

 Rapid City, S. Dak. 



6. Cymbella affinis Kiitz. Bacill., p. 80, pi. 6, fig. 75. 1844. 

 PI. 16, fig. 593. 



Semi-elliptical or semi-lanceolate, 25-40 ;u, long, 7-1 3 /a wide; 

 dorsal margin convex, ventral margin nearly straight, slightly gib- 

 bous, ends rounded, sometimes more or less capitate ; raphe curved 

 toward the dorsal margin ; striations extending nearly to the raphe, 

 not shortened opposite the central nodule except the central one 

 on the ventral side, which is shorter, and in the space which is 

 left by it there is a single dot; striations 9-1 1 in 10 ^u on the dorsal 

 side in the middle, closer elsewhere, finely granular, radiate. 



In creeks : Crawford, Meadow. 



7. Cymbella naviculiformis Auersw. in Kirch. Alg. ScJilcs., p. 



187. 1878. 



PI. 16, figs. 594-598- 



Elliptic-lanceolate, 30-48 /* long, 9-16 /x wide, apices attenuate- 

 rostrate or capitate ; raphe nearly straight ; striations radiate, 10-14 

 in 10 ju. in the middle on the dorsal side, closer elsewhere, short- 

 ened, leaving a narrow space along the raphe, those opposite the 

 central nodule more shortened, leaving a rounded space. 



In lakes, creeks, etc. : Andrews, Clear Lake, Dunning, Hackberry Lake, 

 Pelican Lake, Thedford, Whitman. 

 Weta, S. Dak. 



8. Cymbella aequalis \Y . Sm. Brit. Diat., II. p. 84. 1856. 

 Cymbella ohtusa Greg, in Mic. Journ., IV, p. 5, pi. i, fig. p. 



PI. 16, figs. 599-600. 



