Intermediate forms occur between N. rhyncocephala and N. cryptocephala.
Pl. [31], Fig. 9.
NAVICULA LONGA (GREG.) RALFS
Valve slender, rhombic, elongated, with acute ends; axial area indistinct; central area small; striæ, 6 or 7 in 10 µ, radiate in the middle, elsewhere transverse; central pores closely approximate. L. 120 µ.
New Rochelle, N. Y.
Pl. [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.
Mesoleiæ Cl.
Valve linear or elliptical; axial area narrow; central area quadrate; striæ radiate, finely punctate.
NAVICULA MUTICA KUETZ.