The Diatoms of Nebraska 53 



5. Fragilaria harrisonii (W. Sm.) Grun. Oest. Diat., p. ^6g. 

 1882. 



Odontidium harrisonii W. Sm. Brit. Diat., II, p. 18. 18^6. 



PI. 2, fig. 86. 



Cells cruciform, 20-50 /x long; striations very distinct, shortened, 

 leaving a broad rachis, 4-5 in 10 /x. 



Burge, Long Pine, North Platte, St. Paul, Valentine. 



Fossil : Agate. 



Blackpipe, Rapid City, S. Dak. 



14. Synedra 



Synedra Ehr. in Ber., p. 40. 18^0. 



Etym., Gr. awiSptov, sitting together, the cells being united in 

 clusters. 



Dcsmogonimn Ehr. ; Echinella Breb. ; Exilaria Grev. ; Tabularia 

 Kiitz. 



Cells usually attached, single or in fan-shaped clusters, sessile or 

 stipitate ; very much elongated, more or less lanceolate-linear, some- 

 times more or less wrinkled ; usually with a pseitdoraphe, some- 

 times with false central and polar nodules ; chromatophores, two 

 plates with lobed margins. 



A. Striations extending throughout nearly the breadth of the valve. 

 b. Valves with a pseudonodule. i. S. pulchclla. 



bb. Without a pseudonodule. 



c. With median hyaline space (hyaline space sometimes lacking"). 

 d. Narrowly linear-lanceolate. 



e. Striations distinct, about 13 m 10 m. 



2. S. tcnuissiDia. 

 ee. Striations fine, 16-18 in 10 m. 3. S. radians, 



dd. Linear-oblong or lanceolate. 4. S. familiaris. 



ddd. Narrowly linear. 5. S. ulna, 



cc. Without median hyaline space. 



d. Very large with apices triangular-capitate. 



6. 5". capitata. 

 dd. Not triangular-capitate. 



e. Cells large. 5. S. ulna. 



ee. Cells small. 



/. Striations and pseudoraphe distinct. 



7. 5". amphiccphala. 

 ff. Striations fine; pseudoraphe indistinct. 



8. 5". famelica. 

 AA. Striations marginal. 9. S. tahulata. 



