11. _Grunowia._--As in the group Epithemioideæ, except that the costæ are shorter, not extending across the valve; keel very excentric. 12. _Scalares._--Like Grunowia, but with sharper, somewhat excentric keel; transverse section of frustule quadrangular. 13. _Insignes._--Like Scalares, but with more central keel so that many of the forms are near the group Perrya; frustule somewhat sigmoid. 14. _Bacillaria._--Keel central or nearly so; valve somewhat arched; keel sharp, as in the group Insignes. 15. _Vivaces._--Keel moderately excentric; valve, according to position, semi-lanceolate, with keel puncta in short rows, or lanceolate with quite central keel. The valves have in many positions a resemblance to Hantzschia, so that N. vivax frequently becomes confounded with a form of H. amphioxys. The median keel puncta are not distant and a central nodule is not evident as is the case in all species of Hantzschia. 16. _Spathulatæ._--Like the group Bacillaria, but usually with very delicate striated valves; keel in valve view usually bordered with two parallel lines. 17. _Dissipatæ._--Like Vivaces and Spathulatæ, but with smaller central keel and without parallel lines. Valves usually small, very delicately striated; no central nodule. 18. _Sigmoideæ._--Keel quite central; no parallel lines; frustule sigmoid; valve without longitudinal furrow; keel puncta not extended; no central nodule evident. 19. _Sigmata._--Like Sigmoideæ, but with a more excentric keel. 20. _Obtusæ._--Like Sigmata, with a more or less excentric keel which has in the middle a small bending to the inside; middle keel puncta somewhat more distant than the others, and between them a central nodule evident. {116}21. _Spectabiles._--Valve large, slightly arcuate, with excentric keel; no longitudinal folds; keel puncta somewhat extended over the valve but much less than in the group Insignes, and often scarcely perceptible. 22. _Lineares._--Keel somewhat excentric, but less than in Spectabiles; frustule straight, sometimes a little constricted in the middle, so that a transition is shown to the groups Dubiæ and Bilobatæ. Valve without longitudinal fold; keel puncta round or somewhat angular, scarcely extended. 23. _Lanceolatæ._--Valve lanceolate, linear-lanceolate or rarely elliptical, with very excentric keel; not folded; keel puncta not extended. 24. _Nitzschiella._--Valve with excentric keel and long, produced apices. TRYBLIONELLA NITZSCHIA TRYBLIONELLA HANTZSCH Valve elliptical-lanceolate, with subacute apices; longitudinal fold well marked; striæ coarse, transverse, 5 in 10 µ; indistinct puncta intermediate between the striæ. L. 45 µ. Quite variable. Blue clay. Pl. 32, Fig. 8. NITZSCHIA GRANULATA GRUN. Valve elliptical or elliptical-lanceolate; striæ in double rows, each row of three or four small puncta along the margin and rows of large puncta about 6 in 10 µ across the valve. L. 28-44 µ. Blue clay. Along the coast. Pl. 32, Fig. 3.