I have not seen any specimens south of New England, but they will probably occur.
(4) Striæ Alike, Extremities Produced
GYROSIGMA FASCIOLA (EHR.) CL.
Valve lanceolate, attenuated into curved beaks turned in opposite directions; raphe central, straight, except at the beaks; transverse striæ, 22, longitudinal, 24 in 10 µ (Per.).
New York Bay.
Pl. [23], Fig. 9.
Frustulia AG. (1824); em. GRUN. (1865)
(frustulum, a small piece)
Valves naviculoid, similar, usually free but sometimes enclosed in gelatinous tubes or embedded in mucus. Median line between two thickened ribs. Central and terminal nodules frequently elongated. Surface of valve with fine puncta in longitudinal and transverse lines appearing hyaline under medium powers.
Chromatophores, two, extending along the girdle. They differ from those of Navicula in being separated from the wall in the middle by a hemispherical mass of protoplasm. According to Pfitzer, each chromatophore is divided in the middle, allowing a connection between the hemispherical mass and the central plasma mass. Schmitz states that the chromatophore is thickened in the middle and contains a pyrenoid.