Fig. 5 represents the formation of a sporangial frustule which differs from the usual form in its inflated ends prolonged into rostrate apices. Figs. 1 and 6 are sporangial frustules.
SYNEDRA BICEPS (KUETZ.) SCHMIDT
Valve sublanceolate, inflated at the ends, apices rounded; central space not always distinct; pseudoraphe narrow; striæ radiate at the ends.
This is not Kuetzing's species, if the descriptions and figures are accepted, nor is it H. L. Smith's Type No. 545, which is S. ulna var. danica, nor is it S. biceps Wm. Smith, but it is exactly Schmidt's form (Atlas, Pl. 303, Figs. 10-15).
Schuylkill River.
Pl. [11], Fig. 3.
SYNEDRA DANICA KUETZ.
Valve lanceolate, suddenly constricted at the rounded apices; central space frequently absent.
Very common in streams.
Pl. [11], Fig. 2.