94 THE DIATOMACE.E OF PHILADELPHIA AND VICINITY 



these three species the lateral areas are more or less striated or punctate. Cleve does not 

 consider this a distinction of any importance, although certain varieties are founded upon 

 it. All three species are very common in the blue clay and along the coast, but their 

 varieties are too numerous to describe or figure. 



NAVICULA SPECTABILIS VAR. EMARGINATA CL. 



Valve elliptical; lateral areas broad, narrowed in the middle, delicately striated; mar- 

 ginal striae, 10 in 10 M- L. 70 /x. 

 Blue clay. 

 PL 25, Fig. 7. 



NAVICULA PYG1VLEA KUETZ. 



Valve elliptical, appearing hyaline; axial and central areas faint; lateral areas con- 

 vergent in the middle; striae indistinct, about 25 in 10 M. L. 23 ju. 

 Brandywine Creek (Palmer). 

 PL 27, Fig. 23. 



DECUSSATE CL. 



Valve elliptical or lanceolate; axial area narrow; central area small; striae punctate, 

 in transverse and oblique, curved rows. 



NAVICULA PLACENTA EHR. 



Valve elliptical, with short, rostrate-capitate ends; axial area narrow; central area 

 elliptical; striae in two directions, the transverse about 22 (to 27, CL) in 10 ju, the 

 oblique striae crossing in both directions in curved lines appearing "coarser than the trans- 

 verse" (Lewis). 



A very peculiar species which, as Cleve remarks, seems not to be allied to any other. 

 L. about 35 p, quite constant in size. It is reported from Finland, Scotland, Hungary and 

 New Zealand. Dr. Lewis found it in the Delaware River. It is occasional in the Schuyl- 

 kill River and the blue clay, and very abundant on Marchantia and mosses on the wet 

 rocks of the upper Wissahickon (F. J. Keeley). 



PL 27, Fig. 17. 



LlNEOLATjE CL. 



Valve more or less lanceolate; axial area narrow or indistinct; striae radiate or parallel, 

 lineate, that is, with the puncta closer than the striae. 



NAVICULA RADIOSA KUETZ. 



Valve lanceolate with sub-rostrate apices; axial area indistinct; central area small; 

 striae radiate in the middle, from 6 to 8 in 10 M, and convergent at the ends, about 12 in 



10 M. L. 47 M. 



Very common in fresh water. 

 PL 26, Fig. 17; PL 40, Fig. 9. 



NAVICULA PEREGRINA EHR. 



Valve lanceolate, obtuse; axial area narrow; central area large, rounded or slightly 

 irregular; striae coarse in the middle, 5 in 10 /i, radiate; convergent at the ends, 7 or 8 in 10 ju. 

 Abundant in brackish water. Delaware River. 

 PL 26, Fig. 20. 



