Both of these varieties, with numerous intermediate forms, are abundant near Newtown Square. Varieties of Grunow, known as breve, ovate-lanceolate; productum, ovate-lanceolate with produced apices; capitulatum, lanceolate with capitate extremities, are mingled together in the same gathering. DIATOMA ANCEPS (EHR.) KIRCHN. Valve linear with rostrate apices; costæ robust; striæ delicate, 20 in 10 µ. Zone view quadrangular. Common in fresh water. Pl. 10, Figs. 5 and 6. Fig. 11, Pl. 40, shows frustules containing the nuclei and chromatophores. DIATOMA HIEMALE (LYNG.) HEIB. Valve ovate-lanceolate to lanceolate; apices obtuse, not produced. Costæ not numerous, robust; striæ moniliform. Zone view quadrate, the costæ as septa deeply dividing the valve into convex elevations. Common in springs. Pl. 10, Figs. 7 and 8. In all species of Diatoma a punctum, or pore, is observed, usually at alternate ends of the two valves, by means of which a communication exists between adjoining frustules and causes them to adhere in zig-zag chains when partially separated. PLAGIOGRAMMA GREV. (1859) (plagios, on the side, and gramma, a letter) Frustules quadrangular, adnate in fasciæ, or free. Valve linear, elliptical, or elliptical-lanceolate, divided by two or more median and two terminal costæ or with a central and two terminal hyaline spaces. Valve with two median and two terminal costæ: Linear, pseudoraphe distinct pygmæum Linear, with striæ at the ends wallichianum Ovate-lanceolate obesum Valve without costæ but with central and terminal nodules: pseudoraphe absent tessellatum {43}PLAGIOGRAMMA PYGMÆUM GREV. Valve linear-elliptical; pseudoraphe distinct; rows of granules transverse, usually six in each compartment, moniliform, three on each side. Blue clay. Not common. Pl. 10, Fig. 13. PLAGIOGRAMMA WALLICHIANUM GREV. Valve linear, rounded at the ends; pseudoraphe absent; transverse rows of granules, six or seven in each compartment, and two or three rows of smaller granules at each end. Blue clay. Not common. Pl. 10, Fig. 14. PLAGIOGRAMMA OBESUM GREV. Valve rhombic-lanceolate, the costæ scarcely visible; pseudoraphe rather wide; rows of granules, about seven in each compartment, slightly radiating. Blue clay. Not common. Pl. 10, Fig. 12. PLAGIOGRAMMA TESSELLATUM GREV. Valve elliptical-lanceolate; central space transversely elliptical to the major axis, half the diameter of the valve; terminal spaces more or less circular or ovate. Granular markings large, quadrangular, in transverse rows. Pseudoraphe not distinct. As the central space does not reach the margin, it is a question whether this form is a Plagiogramma or a new genus. Blue clay. Rare. Pl. 10, Fig. 11. OPEPHORA PETIT (1888) (ope, an opening, and phoreo)