SECTION 1. Surirella Biseriata (ehr.) Bréb.

SURIRELLA BISERIATA (EHR.) BRÉB.

Valve lanceolate, subacute at the ends; costæ robust, about 2 in 10 µ, parallel in the middle, radiate at the ends; pseudoraphe narrow. L. 100 µ.

Surirella bifrons Ehr.

Fresh water.

Pl. 39, Fig. 12; Pl. 35, Fig. 2 (smaller form).

SURIRELLA LINEARIS WM. SM.

Valve linear, with cuneate ends, slightly constricted in the middle; costæ parallel, 2-3 in 10 µ. L. 90 µ.

Fresh water.

Pl. 35, Fig. 8.

SURIRELLA AMPHIOXYS WM. SM.

Valve oblong-linear, with cuneate ends; pseudoraphe narrow; costæ, 3-4 in 10 µ; striæ, 14-16 in 10 µ, somewhat radiate. L. 34-54 µ.

Surirella moelleriana Grun.

Fresh and brackish water. Common along the coast.

Pl. 35, Figs. 12 and 13.

SURIRELLA ROBUSTA EHR.

Valve linear-ovate; pseudoraphe wide; alæ prominent; costæ wide, 1¼ in 10 µ. Frustule in zone view clavate. L. 200-365 µ.

Fresh water.

Pl. 36, Fig. 2.

{125}SURIRELLA SPLENDIDA (EHR.) KUETZ.

Valve ovate; costæ, 1½ to 2 in 10 µ; pseudoraphe linear, narrow. L. 125-200 µ.

Fresh water.

Pl. 35, Fig. 3.

S. splendida is smaller than S. robusta and wider in proportion, but, as intermediate forms occur, it is difficult to distinguish between them.

SURIRELLA ELEGANS EHR.

Valve ovate, rounded at one end and acute at the other; pseudoraphe lanceolate, narrow; costæ, 1½ in 10 µ; striæ subtle, 22 in 10 µ. Frustule in zone view cuneate. L. 180-220 µ.

Fresh water.

Pl. 36, Fig. 1.

SURIRELLA STRIATULA TURPIN

Valve broad, obovate or elliptical, rounded at each end; costæ, 1¼ in 10 µ, curved at the ends; striæ, 14 in 10 µ. Frustule in zone view cuneate; marginal alæ quite robust. L. 100-160 µ.

Blue clay. Brackish water.

Pl. 34, Fig. 1.

In the specimen figured, the outline is exactly elliptical, although the species is usually conical at one end.

SURIRELLA GEMMA EHR.

Valve ovate or ovate-elliptical, rounded at each end, sometimes asymmetrical along the longitudinal axis; pseudoraphe very narrow; costæ distant, at irregular intervals, about 2 in 10 µ, somewhat radiate, reaching the pseudoraphe; striæ, 20 in 10 µ, punctate. Frustule in zone view cuneate. L. 70-120 µ.

Along the coast.

Pl. 36, Fig. 4.

SURIRELLA TENERA GREG.

Valve ovate; pseudoraphe narrow, well-defined; costæ indistinct, 2½ in 10 µ, their margins invisible; striæ about 14 in 10 µ, punctate, more evident near the margin. L. 90 µ.

Surirella diaphana Bleisch.

Pavonia, N. J., artesian well.

Pl. 35, Fig. 6.

The figure is that of the var. nervosa A. S. (Atlas, Pl. 23, Fig. 15), which differs from the type in having the position of the costæ indicated by scattered puncta.

{126}SECTION 2

SURIRELLA GUATIMALENSIS EHR.

Valve ovate; pseudoraphe very narrow and indistinct; costæ short, marginal, 2-2½ in 10 µ, absent from the rounded end. L. 120 µ.

Surirella cardinalis Kitton.

Smith's Island, Delaware River.

Pl. 36, Fig. 5.

SURIRELLA OVALIS BRÉB.

Valve ovate; costæ short, marginal, radiate, 3-6 in 10 µ, often unequal; central area ovate, indistinctly costate; striæ scarcely visible, about 18 in 10 µ; pseudoraphe narrow. L. 45-93 µ.

Surirella davidsonii A. S.

Fresh or brackish water.

Pl. 35, Fig. 5; Pl. 39, Fig. 11.

The smaller specimen is from the Delaware River, and the larger from the Hudson River.

SURIRELLA CRUMENA BRÉB.

Valve nearly orbicular; costæ short, marginal, radiate; pseudoraphe narrow, indistinct; central area indistinctly costate, sometimes interrupted.

On account of the extreme confusion in the names of many forms which appear to be variations of S. ovalis, I have followed Van Heurck in retaining the original names as specific. De Toni gives S. crumena as a variety of S. ovalis.

Fresh and brackish water. Quite common in the Delaware River.

Pl. 35, Fig. 4.

SURIRELLA PINNATA WM. SM.

Valve ovate or oblong-ovate; costæ reaching the linear pseudoraphe, about 6 in 10 µ. L. 40 µ.

Surirella ovalis var. pinnata (Wm. Sm.) De Toni.

S. pinnata is the type of a number of small forms usually found together, including S. panduriformis, S. angusta and S. minuta.

Fresh water. Media (Palmer).

Pl. 36, Fig. 7; Fig. 9 (abnormal).

Var. minuta, a small form of S. pinnata, occurs with the type.

SURIRELLA PANDURIFORMIS WM. SM.

Valve linear-oblong, with rounded ends, more or less constricted in the middle; otherwise as in S. pinnata. L. 54 µ.

Fresh water.

Pl. 36, Fig. 6.

{127}SURIRELLA ANGUSTA KUETZ.

Valve linear, with cuneate ends; otherwise as in S. pinnata.

Fresh water.

Pl. 36, Fig. 8.

S. pinnata, S. panduriformis, and S. angusta have a narrow central area, and differ from S. ovalis which has short costæ.

SURIRELLA OBLONGA EHR. ?

Valve elliptical-lanceolate, with obtuse ends; costæ, marginal, 2½ in 10 µ; median area granulate; pseudoraphe narrow, lanceolate, scarcely visible; striæ about 18 in 10 µ. L. 60 µ.

Blue clay. Rare.

Pl. 35, Fig. 9.

This has the outline and appearance of S. oblonga Ehr. (Mik. Pl. 15, Fig. 48), but the costæ are closer.

SURIRELLA RECEDENS A. S.

Valve ovate; costæ, 2-2½ in 10 µ; pseudoraphe narrow, not reaching the ends of the valve; intercostal spaces more evident near the middle. L. 50 µ.

Blue clay. Not uncommon.

Pl. 35, Fig. 7.

SURIRELLA CRUCIATA A. S.

Valve ovate; pseudoraphe very narrow; costæ, 2 in 10 µ; the outline of several of the median costæ strongly emphasized, while the other costæ are indistinct. L. 54 µ.

Blue clay.

Pl. 35, Fig. 10.

SURIRELLA GRACILIS GRUN.

Valve linear, with sub-cuneate ends, slightly constricted in the middle; pseudoraphe very narrow; costæ, 6-7 in 10 µ; transverse striæ about 26 in 10 µ, punctate. L. 75 µ.

According to De Toni (p. 598), this form is a Nitzschia. It has, however, a narrow pseudoraphe.

Pavonia, N. J., artesian well. Rare.

Pl. 35, Fig. 11.