Terpsinoë, 34 americana (Bail.) Ralfs, 34 novæ-cæsareæ Boyer, 34 _Tessella_ _interrupta_ Ehr., 38 Trachyneis, 79 aspera var. intermedia Grun., 79 Trachysphenia, 47 australis Petit, 47 _Triceratium_ _alternans_ Bail., 33 _favus_ Ehr., 31 _obtusum_ Br., 33 _pileotus_ Ehr., 30 _punctatum_ Br., 33 _sculptum_ Shad., 33 Trinacria, 30 pileolus (Ehr.) Grun., 30 _Tripodiscus_ _argus_ Ehr., 26 Tropidoneis, 68 lepidoptera (Greg.) Cl., 69 _Tryblionella_ _punctata_ Wm. Sm., 116 _scutellum_ Wm. Sm., 118 _Vibrio_ _paxillifer_ O. F. Mueller, 119 PLATES PLATE 1 MELOSEIRA 3-4 Meloseira roeseana var. epidendron (Ehr.) Grun. 15 5-6 Meloseira roeseana Rab. 15 8-9 Meloseira distans (Ehr.) Kuetz. 14 10 Meloseira granulata (Ehr.) Ralfs 15 11-12 Meloseira sulcata Kuetz. 15 15-16-17 Meloseira undulata (Ehr.) Kuetz. 15 GAILLONELLA 13-14 Gaillonella nummuloides (Dillw.) Bory 16 LYSIGONIUM 7 Lysigonium moniliforme (Muell.) Link. 16 18-19 Lysigonium varians (Ag.) De Toni 17 HYALODISCUS 20 Hyalodiscus scoticus (Kuetz.) Grun. 18 21 Hyalodiscus radiatus var. arctica Grun. 17 22 Hyalodiscus stelliger Bail. 17 NOTE.--The figures in all of the plates, except when otherwise noted, are magnified 800 diameters. [Illustration: PLATE 1] PLATE 2 STEPHANOPYXIS 1-2 Stephanopyxis turris (Grev.) Ralfs 18 3 Stephanopyxis corona (Ehr.) Grun. 18 CYCLOTELLA 4 Cyclotella meneghiniana var. stelligera Cl. and Grun. 20 5-6 Cyclotella operculata (Ag.) Kuetz. 20 7 Cyclotella comta (Ehr.) Kuetz. 20 8 Cyclotella meneghiniana Kuetz. 19 9 Cyclotella striata (Kuetz.) Grun. 19