THE DIATOMACE^ OF PHILADELPHIA AND VICINITY 97 



NAVICULA OBLONGA KUETZ. 



Valve linear-lanceolate, with broad, rounded ends; margin sometimes undulate; axial 

 area narrow; central area large, orbicular; striae in the middle distant, radiate, convergent 

 at the ends and curved or sharply bent, 7 in 10 n, lineate. L. 70-200 M (Cleve). 



Blue clay. Occasional in fresh water. 



PI. 27, Fig. 21. 



NAVICULA HASTA PANT. 



Valve lanceolate, gently tapering to the obtuse, produced ends; axial area lanceolate, 

 widened to an orbicular space in the middle; striae radiate, the median coarse and quite 

 distant, 5 in 10 n, becoming closer at the ends where they are 12 in 10 ju, lineate. The dis- 

 tance between the median strise gives the appearance of a stauros. 



Occasional in the blue clay. 



PI. 27, Fig. 13. 



NAVICULA HASTA VAR. PUNCTATA N. VAR. 



Valve as in type but with strise in the middle distinctly punctate and reaching the 

 median line. 



Greenwich Point, Philadelphia. 

 PI. 27, Fig. 14. 



NAVICULA RHYNCOCEPHALA KUETZ. 



Valve lanceolate, with produced ends ; axial area indistinct ; central area small, rounded ; 

 striae radiate in the middle, convergent at the ends, 10-11 in 10 p., punctate. L. 42 /j. 

 Fresh water. Common. 

 PL 31, Fig. 8. 



NAVICULA CRYPTOCEPHALA KUETZ. 



Valve lanceolate, with rostrate ends; axial area indistinct; central area small; striae, 

 16 in 10 /a, lineate, radiate in the middle, convergent at the ends. L. 28 n. 

 Common in fresh water. 



Intermediate forms occur between N. rhyncocephala and N. cryptocephala. 

 PI. 31, Fig. 9. 



NAVICULA LONGA (GREG.) RALFS 



Valve slender, rhombic, elongated, with acute ends; axial area indistinct; central 

 area small; striae, 6 or 7 in 10 /*, radiate in the middle, elsewhere transverse; central pores 

 closely approximate. L. 120 p.. 



New Rochelle, N. Y. 



PI. 31, Fig. 10. 



Cleve refers this form to N. directa var. remota Grun. Some specimens are found in 

 this locality showing the "generally twisted" median line mentioned by Gregory. 



MESOLELE CL. 



Valve linear or elliptical; axial area narrow; central area quadrate; striae radiate, 

 finely punctate. 



NAVICULA MUTICA KUETZ. 



Valve ovate, elliptical or lanceolate; axial area narrow; central area dilated into a 

 stauros not reaching the margin; striae about 20 in 10 n, more distant in the middle, 

 radiate, punctate. A punctum occurs on one side of the central nodule. 



