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.