86 Clarence J. Elmore 



shortened around the central nodule, but not alternately long and 

 short, distinctly punctate, sometimes coarsely so. 



Among other algae in creeks, rivers, and ponds, also fossil : Grand 

 Island. 



Fossil : Mullen. 

 Turtle River, S. Dak. 



Professor Cleve, Syn. Nar. Diat., II. p. 2^, says of these three 

 species: " Navicula placentula is very nearly akin to Navicula 

 gastrum\, and it is questionable whether they should not be united 

 into one species. The median striae are in Navicula gastruvi, but 

 not in Navicula placentula, alternately longer and shorter, but this 

 characteristic is subject to great variation, the variety jenisseyensis 

 having only a few, and the variety latiscula no shorter median 

 striae. Of more importance is it that Navicula placentula has 

 coarsely lineate, or almost punctate striae. Navicula anglica is 

 nearly akin to Navicula gastruin and might be considered a variety 

 of it. There exists, in fact, no limit between these three species. 

 * * * On the other hand, Navicula placentula is by its coarsely 

 punctate striae allied to the section Punctatae, among which 

 Navicula amphibola is nearly akin to Naz'icula placentula. Smaller 

 forms of Navicula gastrum closely resemble smaller forms of 

 Navicula peregrina var. inenisculus, from which they differ by the 

 terminal striae being radiate throughout, but this characteristic is 

 sometimes exceedingly delicate." 



39. Navicula dicephala (Ehr.) Kiitz. BacilL, p. ()6, pi. 28, figs. 

 60, 62. 1844. 



Pinnularia dicephala Ehr. Inf., p. 18 j. i8j8. 



PI. 9, figs. 346-350. 



Linear to linear-lanceolate, with rostrate-capitate ends. 17-40JU, 

 long, 5-12 /A wide; striations granular, 8-12 in 10 ju., all radiate, 

 those around the central nodule usually shortened, but not alter- 

 nately, leaving a transverse hyaline space. 



In creeks, lakes, rivers, also fossil : Andrews, Ansehno, Benkleman, 

 Brownlee, Central City, Clear Lake, Cody Lake, Crawford, Dismal River, 

 Dunning, Fairbury, Fremont, Gordon Creek, Grand Island, Hackberry 

 Lake, Halsey, Holbrook, Long Pine, Louisville, New Helena, Norfolk, 

 Oakdale, O'Neill, Orella, St. Paul, Seneca, Snake River, Thedford, Val- 

 entine, Wann, West Point, Whitman. 



