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. The figure represents an unusually large form. It differs from S. ulna only in its apices. SYNEDRA CAPITATA EHR. Valve long, linear, dilated into triangular acute apices; pseudoraphe distinct; striæ radiate at the ends. Blue clay. Pl. 11, Fig. 8. SYNEDRA ACUS KUETZ. Valve very narrow, lanceolate, acicular, with obtuse apices. Common in the Schuylkill River. Pl. 11, Figs. 9 and 18. SYNEDRA GOULARDI BRÉB. Valve constricted in the middle; apices sub-acute, sometimes slightly rostrate or capitate; central space evident. Neshaminy Creek (Palmer). Blue clay. Crum Creek. Pl. 11, Figs. 12 and 13. SYNEDRA PULCHELLA (RALFS) KUETZ. Valve lanceolate, tapering to the sub-acute, rostrate or slightly capitate apices; dilated at the central hyaline space; pseudoraphe distinct. Very variable in size. Crum Creek. Schuylkill River. Rather common. Pl. 11, Figs. 14, 15, 16. SYNEDRA PULCHELLA VAR. ABNORMIS MACCHIATI? Valve as in type form, except that one end is curved like a beak, as in S. hamata Wm. Sm., which it resembles. Not uncommon in the Schuylkill River. Pl. 11, Fig. 17. SYNEDRA OXYRHYNCHUS VAR. UNDULATA GRUN. Valve linear-lanceolate with produced rostrate apices, asymmetrical, sigmoid; pseudoraphe narrow; pseudo-nodule large. Common in fresh water. Pl. 12, Fig. 1. {49}SYNEDRA PULCHELLA VAR. FLEXELLA N. VAR. Frustule slightly attenuated at the ends, truncate, somewhat tumid in the middle and flexed. Valve lanceolate, with obtuse or subcapitate apices and with two almost imperceptible constrictions at the middle producing a tumid appearance; pseudoraphe distinct; pseudo-nodule absent. L. 56 µ; striæ, 14-16 in 10 µ. Some valves are bent and incised on one side. The outline of the valve is that of pulchella. Common at Newtown Square. Pl. 12, Fig. 2. SYNEDRA RADIANS KUETZ. Frustules linear, in small fasciæ. Valve 34 µ in length, linear, with apices rostrate, obtuse, sometimes slightly capitate; pseudoraphe distinct; striæ about 20 in 10 µ. Fresh water. Pl. 10, Figs. 32 and 33.