Valve lanceolate, suddenly constricted at the rounded apices; central space frequently absent.
The figure represents an unusually large form. It differs from S. ulna only in its apices.
Valve long, linear, dilated into triangular acute apices; pseudoraphe distinct; striæ radiate at the ends.
Valve very narrow, lanceolate, acicular, with obtuse apices.
Valve constricted in the middle; apices sub-acute, sometimes slightly rostrate or capitate; central space evident.
Neshaminy Creek (Palmer). Blue clay. Crum Creek.
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.
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.
Valve linear-lanceolate with produced rostrate apices, asymmetrical, sigmoid; pseudoraphe narrow; pseudo-nodule large.
{ 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.
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.
There is difficulty in recognizing S. radians K. as described and figured by different authors. On Plate 12, Fig. 8, I have drawn a specimen from H. L. Smith's Type Slide No. 574, labelled S. radians Kuetz., not Wm. Smith, which, however, corresponds closely to Smith's figure (Brit. Diat. 1, Pl. 11, Fig. 89). De Toni gives S. radians Kuetz. as equivalent to S. tenera Wm. Sm. Van Heurck's figure of S. radians, and also the figure of ulna var., said to be synonymous with H. L. Smith's S. radians, which does not correspond to the specimens on Smith's slide in my possession, are confusing. In Van Heurck's Synopsis the striæ are said to be 16 or 17, while De Toni describes them as subtle and from 17 to 24 in 10 µ. The length is quite variable.