io6 Clarence J. Elmore 



centric; transverse striations 20-23 in 10 ^u,, longitudinal 24-27 in 



lO/A. 



In San Joaquin River, Stockton, Cal. 



5. Gyrosigma spencerii (W. Sm.) CI. Syn. Nav. Dial., I, p. 117. 



i8p4. 

 Pleurosigma spencerii W. Sm. in Ann. Nat. Hist., p. 12, pi. 2, 



fig. 15. 1852. 

 PI. 13, figs. S18-519. 



Linear-lanceolate, 58-220 /* long, 10-25 /a wide, tapering toward 

 the rounded ends ; transverse striations more distant than the 

 longitudinal; transverse 17-22 in 10 /x, longitudinal 22-24 in lO/*; 

 raphe sigmoid, median. 



In creeks, rivers, ponds, etc. : Brock, Crete, Grand Island, Johnson, 

 Lincoln, Norfolk, Peru, Pleasant Dale, Rulo, St. Michael, Salem, Stroms- 

 burg, Talmage, Wahoo, Weeping Water, West Point. 



Stockton, Cal.; Emporia, Kansas. 



6. Gyrosigma scalproides (Rabenh.) CI. Syn. Nav. Diat., I, p. 



118. i8p4. 



Pleurosigma scalproides Rabenh. Alg. Eu., No. iioi. 186 1. 



PI. 13, fig. 520. 



Linear, slightly sigmoid, 57-58/4 long, 9-10/1 wide, apices 

 obliquely rounded ; raphe median, nearly straight ; central nodule 

 elongated ; transverse striations more distant than the longitudinal, 

 transverse about 22 and longitudinal about 29 in lo/t. 



In creeks with Spirogyra, Oscillatoria, etc. : Alma, Cook, Grand Island, 

 Lincoln, Norfolk, Orleans, Stanton, Talmage, Weeping Water, West 

 Point. 



Stockton, Cal. 



7. Gyrosigma attenuatum (Kiitz.) CI. Syn. Nav. Diat., I, p. 



115. 1894. 



F.rustulia attenuata Kiitz. Dec, No. (?j (according to Lagerst.). 



PI. 23, fig. 857. 



Sigmoid, tapering from the middle to the obtuse ends, 180-260 /* 

 long, 25-28/* wide; raphe central; longitudinal striations 10-12 in 

 lO/x, transverse striations 14-16 in 10 /t. 



Dunning, Norfolk. 



Fossil in Pleistocene stratum, Valentine. 



