Valve elongated, asymmetrical with respect to the transverse axis; striæ transverse, usually radiate, punctate. Chromatophore band single, the middle lying on one zone. In conjugation, according to Thwaites and Pfitzer, from two mother cells, which do not form a positive union, two auxospores are developed parallel to the original frustules. In Plate 19, Fig. 19, I have drawn a representation of the auxospore formation as I have frequently observed it in a gathering sent me by Mr. T. C. Palmer, containing G. angustatum, a common species in this locality. The sagittal plane of the valve of the auxospore is at right angles to the plane of the valve of the mother cell. Two valves of one of the mother cells are seen separated, one on each side of the auxospore which is nearly twice the length of the original frustules. The two valves of the other mother cell are not shown as they are not usually found closely united. In the figure one valve alone of the auxospore is seen, the opposite valve not being in focus. The valves of the auxospore are usually more or less arcuate, as in Cymbella, to which the genus is closely allied. Grunow divides Gomphonema into two groups, Asymmetricæ and Symmetricæ, according to the presence or absence of stigmas. Cleve suggests Stigmaticæ and Astigmaticæ as more suitable in order to agree with the Cymbellæ. The Stigmaticæ are found chiefly in fresh water, sometimes in brackish. All of the marine forms belong to the Astigmaticæ, which, however, include some common fresh-water forms. Many species of Gomphonema are stipitate, some occur in gelatinous masses, and others are free. {71}GOMPHONEMA MONTANUM SCHUM. Valve slightly biconstricted, with obtuse apex and basis, somewhat cuneate; axial area linear, widened in the middle unilaterally; stigma, one; striæ about 11 in 10 µ, more distant in the middle, punctate. _Gomphonema subclavatum_ var. _montana_ (Schum.) Cl. Pavonia, N. J., artesian well. Rare. Pl. 19, Fig. 3. GOMPHONEMA GEMINATUM LYNG. Valve biconstricted, with large, rounded, sub-truncate apex and broad, sub-truncate basis; striæ, 9 in 10 µ, radiate in the middle, alternately longer and shorter, transverse at the basis and near the apex where they again radiate, coarsely punctate, puncta, 12 in 10 µ. Axial area linear; central area rounded, with several large stigmas in a longitudinal row; terminal fissures hook-shaped. Blue clay. Pl. 19, Fig. 4. GOMPHONEMA LANCEOLATUM VAR. INSIGNIS (GREG.) CL. Valve lanceolate; axial area narrow; central area unilateral with one stigma; striæ with coarse and distant puncta. Common and variable. _Gomphonema insigne_ Greg. Pl. 19, Figs. 6 and 12. Fig. 12 shows a unilateral central area. Fig. 6 is more clavate in outline with small central area. In both forms the coarse puncta are in distinct longitudinal lines in the middle. GOMPHONEMA ACUMINATUM VAR. TURRIS (EHR.) CL.?