This species can scarcely be referred to Dillwyn's Conferva pectinalis, as, in his description, quoting Mueller, he says that "the filaments are of a dirty green color; seldom exceeding half an inch in length." Dillwyn's form is probably Fragilaria virescens, which equals Fragilaria pectinalis Ehr., while Kuetzing's species is Fragilaria pectinalis Ralfs. It is not impossible to confuse Fragilaria virescens and Eunotia pectinalis when the zone only is seen under a low power and their mode of growth is similar.
EUNOTIA PECTINALIS VAR. UNDULATA RALFS
Valve as in type form, but with undulate margins.
Common in the cedar swamps of New Jersey.
Pl. [13], Figs. 8 and 10.
EUNOTIA PECTINALIS VAR. SOLIEROLII (KUETZ.)
Valve as in type, but with internal divisions as though in the process of reduplication.
Not common. Moorestown, N. J. (Palmer).
Pl. [13], Fig. 9.
EUNOTIA PECTINALIS VAR. VENTRICOSA GRUN.