Valve elliptical or panduriform; median line enclosed in strongly siliceous horns corresponding to the lyre-shaped areas of Navicula lyra but never punctate; central nodule, quadrate; valve costate, or striate, or both; between the horns and the outer part are thinner spaces or sulci, and, in some species, outside of the sulci are narrow spaces known as lunulæ. Chromatophores, two, upon the girdle or the valves. Pyrenoids have been found in one species only, D. interrupta. DIPLONEIS ELLIPTICA (KUETZ.) CL. Valve elliptical; central nodule large; sulci narrow, curved, close to the horns; striæ punctate, in rows radiating more and more toward the ends. Variable in size and in the coarseness of puncta which are from 10 to 13 in 10 µ (Cleve). Cleve describes D. ovalis Hilse as having the central nodule rounded, but otherwise about the same as D. elliptica, and as equivalent to Navicula ovalis A. Schmidt (Atlas, Pl. 7, Figs. 33 to 36). Very common in fresh water and occasional in brackish. Pl. 20, Fig. 14. DIPLONEIS SMITHII (BRÉB.) CL. Valve elliptical; central nodule not broad; furrows evenly curved on the outer edge, crossed by costæ and double oblique rows of alveoli. Variable in size and in the curvature of the furrows. Cleve forms a new species, D. major, of the large form figured by Schmidt (Atlas, Pl. 7, Figs. 18, 19, 21 and 22), stating that the structure is much coarser and the form is larger with broad furrows. In the specimen here figured the size is median and the furrows are as in D. major. Marine and brackish. Common. Pl. 20, Fig. 17. {85}DIPLONEIS CRABRO VAR. PANDURA (BRÉB.) CL. Valve constricted, segments tongue-shaped; central nodule small; horns narrow, nearly parallel, with a row of large puncta; costæ, 4 in 10 µ, convergent in the middle, radiating at the ends, alternating with a double row of puncta, 11 in 10 µ. Pavonia, N. J. (artesian well). Pl. 20, Fig. 4. DIPLONEIS CRABRO VAR. EXPLETA (A. S.) CL. Valve slightly constricted, segments tongue-shaped; costæ robust, 5 or 6 in 10 µ, alternating with double rows of rather coarse puncta. L. 56 µ. Port Penn, Delaware River. Pl. 20, Fig. 15. DIPLONEIS CRABRO VAR. PANDURELLA CL.? Valve constricted, the lobes elliptical; central nodule large, with horns parallel in the middle, convergent at the ends; furrows wide, with faint costæ; no lunula; costæ parallel in the middle, radiate at the ends, 9 in 10 µ, alternating with very fine double rows of puncta (not shown in the figure). L. 65 µ. Blue clay. Pl. 20, Fig. 13. DIPLONEIS CRABRO VAR.? Valve constricted, segments elliptical; costæ, 8 in 10 µ, converging in the middle, radiating at the ends; horns narrow; furrows wide, costate; lunulæ indistinct. L. 75 µ. Resembles var. pandurella except in the convergence of the costæ and in the lunula. Squan River. Marine. Pl. 20, Fig. 9. DIPLONEIS FUSCA VAR. DELICATA (A. S.) CL.