Gyrosigma Hassall (1845)
(gyros, curved, and sigma)
Valve lanceolate, sigmoid; axial area very narrow, central area small; striæ punctate, in transverse and longitudinal rows.
Chromatophores two, in long and narrow bands, perforated, differing from those of Pleurosigma. The elæoplasts are also arranged differently in the two genera. (Mereschkowsky, Études sur l'Endochrome des Diatomées, Imperial Academy of Petrograd, 1901, Vol. 11, No. 6, p. 18 et seq.)
The arrangement is according to Peragallo.
(1) Longitudinal Striæ More Distant Than The Transverse
GYROSIGMA HIPPOCAMPUS (EHR.)
Valve lanceolate, sigmoid, with obtuse ends; raphe nearly central; transverse striæ 15-17, longitudinal, 10-12 in 10 µ.
Navicula hippocampus Ehr.
Pleurosigma hippocampus (Ehr.) Wm. Sm.