(named after Dr. Suriray, a physician of Havre) Valve linear, elliptical or ovate; pseudoraphe linear or lanceolate; a marginal keel forming wings or alæ seen in zone view; costæ short or reaching the pseudoraphe, frequently with intercostal striæ more or less evident. The genus is divided by Grunow according to the length and form of the costæ. I include Stenopterobia. Section 1.--Costæ of nearly equal width throughout, reaching the pseudoraphe. Section 2.--Costæ short or marginal. Section 3.--Costæ dilated at the margin, attenuated toward the pseudoraphe. Section 4.--Valve having the appearance of Nitzschia, with inconspicuous alæ (Stenopterobia). The endochrome consists of two laminate chromatophores, one on each valve. The auxospores are single, originating from the union of two frustules (H. L. Smith). SECTION 1 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.