Valve linear-elliptical, broad; axial area broad, widened in the middle; striæ slightly radiate in the middle, 3 in 10 µ; median line oblique, the terminal fissures hook-shaped. L. 86 µ.
Valve linear, with rounded or sub-truncate ends; axial area about one-fourth the width of the valve, widened in the middle; median line with large hook-shaped terminal fissures; striæ, 4 or 5 in 10 µ. L. 54 µ.
Blue clay. Occasional in fresh water in a smaller form. Specimens occur intermediate between P. lata and P. borealis.
PINNULARIA BOREALIS VAR. SCALARIS (EHR.) CL.
Valve narrow, linear; axial area broad, widened into a transverse fascia; striæ, 8 in 10 µ. L. 32 µ.
Valve linear, with rounded ends; axial area less than one-third the width of the valve, gradually widened in the middle to a transverse fascia; on each side of the central nodule is a lunate space; striæ divergent in the middle, convergent at the ends, 13 in 10 µ; terminal fissures very long, bayonet shaped. L. 75 µ.
Cleve describes a variety continua as not interrupted. In some forms the fascia is marked by very faint, short striæ on the margin.
Valve linear, tapering to the subcapitate ends; axial area dilated in the middle; striæ, 10-11 µ, divergent in the middle, convergent at the ends. L. 80 µ.
Valve linear, gibbous in the middle, ends subcapitate; axial area narrow, widened in the middle to a large orbicular space; striæ strongly divergent in the middle, convergent at the ends, 11 in 10 µ. L. 60 µ.
Valve linear, with slightly triundulate margins tapering to the subcapitate ends; axial area more than one-third the width of the valve, slightly widened in the middle; median line with approximate central pores and semicircular terminal fissures; striæ divergent in the middle, convergent at the ends, 11 in 10 µ. L. 82 µ.
Some of the forms are more triundulate than the specimen figured.
PINNULARIA STAUROPTERA VAR. INTERRUPTA CL.
Valve linear, tapering to the subcapitate ends; axial area broad, widened in the middle to a transverse fascia; striæ divergent in the middle, convergent at the ends, 10 in 10 µ; median pores approximate. L. 118 µ.
Valve linear, gibbous in the middle and tapering to the subcapitate ends; axial area about one-third the width of the valve, widened in the middle; median line with approximate central pores and bayonet-shaped terminal fissures; striæ sometimes unilaterally interrupted, divergent in the middle, strongly convergent at the ends, 9 in 10 µ. L. 138 µ.