Valve large, cymbiform, arcuate on the dorsal, slightly gibbous on the ventral side; axial area linear, broad, slightly widened in the middle; no row of puncta on the ventral side. The puncta form curved longitudinal lines and the innermost row on the ventral side appears sometimes distant from the others, but not as in C. cistula. _Cocconema asperum_ Ehr. _Cymbella gastroides_ Kuetz. {62}Not Cymbella gastroides H. L. Smith, Type No. 118, which is C. mexicana A. S., having a punctum in the middle of the central nodule; in outline it is like C. gastroides var. minor Kuetz. Blue clay. Pl. 18, Fig. 1 (an unusual form, but it resembles Grunow's. (Diat. Franz Jos. Land, Pl. 1, Fig. 7.) CYMBELLA CYMBIFORMIS (KUETZ.) BRÉB. Valve cymbiform, slightly gibbous on the ventral margin; apices broad, somewhat truncate; a punctum occurs on the ventral side of the median line; striæ, 8 in 10 µ, closely punctate. Kirkwood Pond, N. J. Pl. 18, Fig. 2. CYMBELLA CISTULA (HEMPR.) KIRCHN. Valve cymbiform, with gibbous ventral margin and truncate apices; a distinct row of several puncta occurs below the median line in typical forms. Blue clay. Pl. 18, Fig. 3. CYMBELLA LANCEOLATA (EHR.) KIRCHN. Valve cymbiform, with gibbous ventral margin; apices truncate; axial area very narrow, scarcely widened in the middle; striæ with fine close puncta. Kirkwood Pond, N. J. Pl. 18, Fig. 4. CYMBELLA MEXICANA (EHR.) A. S. Valve broad, with gibbous ventral margin and sub-rostrate, truncate apices; median line with reflexed terminal fissures; striæ with coarse puncta; a large punctum occurs in the centre of the central area. Blue clay. Pl. 18, Fig. 5. CYMBELLA TUMIDA (BRÉB.) V. H. Valve cymbiform, with gibbous ventral margin and abruptly rostrate ends; median line arcuate; axial area narrow; central area large, orbicular; below the central nodule is a punctum; striæ punctate. Crum Creek. Pl. 18, Fig. 7. SECTION 3.--ENCYONEMA. FRUSTULES IN TUBES CYMBELLA VENTRICOSA KUETZ. Valve lunate, with straight or slightly gibbous ventral margin; axial area indistinct; median line straight or nearly so; striæ punctate. Very common, but extremely variable. The ventral margin is sometimes straight and sometimes quite gibbous. Pl. 18, Figs. 14, 22; Pl. 38, Fig. 16; Pl. 40, Fig. 8. {63}C. ventricosa is considered by some authors to be equivalent to C. affinis var. semicircularis Lagerst., Encyonema prostratum (Berk.) Ralfs, E. cæspitosum Kuetz. and E. auerswaldii Rab. H. L. Smith's Type Slide of C. ventricosa Ag. is said to equal C. affinis Kuetz., but the specimens appear to me to be equivalent to C. ventricosa Kuetz. Cleve unites many forms, including E. cæspitosum, under C. ventricosa. CYMBELLA PROSTRATA (BERK.) CL.