2 Auricula mucronata (H. L. Smith) Peragallo 69 [Illustration: PLATE 15] PLATE 16 ACHNANTHES 1-2 Achnanthes longipes Ag. 58 3 Achnanthes brevipes Ag. 59 4-5-6 Achnanthes subsessilis Kuetz. 59 7-8 Achnanthes inflata (Kuetz.) Grun. 59 9 Achnanthes coarctata (Bréb.) Grun. 59 10-11-12 Achnanthes lanceolata (Bréb.) Grun. 59 13 Achnanthes danica (Floegel) Grun. (lower valve) 60 14-15 Achnanthes exigua Grun. 59 16-17 Achnanthes linearis forma curta H. L. Smith 59 COCCONEIS 18 Cocconeis scutellum var.? 57 19-20 Cocconeis placentula Ehr. 57 21 Cocconeis scutellum Ehr. (upper valve) 57 22 Cocconeis dirupta Greg. (lower valve) 58 23-24 Cocconeis pediculus Ehr. 57 25-26 Cocconeis pellucida Grun. 58 27-28 Cocconeis scutellum var. ornata Grun. 57 29 Cocconeis placentula var. lineata (Ehr.) V. H. 58 ANORTHONEIS 30-31 Anorthoneis excentrica (Donk.) Grun. 56 [Illustration: PLATE 16] PLATE 17 FRUSTULIA 1 Frustulia lewisiana (Grev.) De Toni 77 2 Frustulia rhomboides (Ehr.) De Toni 77 3 Frustulia rhomboides var. amphipleuroides Grun. 77 4 Frustulia vulgaris (Thwaites) De Toni 77 5 Frustulia interposita (Lewis) De Toni 78 6 Frustulia rhomboides var. saxonica (Rab.) De Toni 77 BREBISSONIA 7 Brébissonia boeckii (Kuetz.) Grun. 79 8 Brébissonia palmerii n. sp. 80 AMPHIPLEURA 9 Amphipleura pellucida Kuetz. 78 10-11 Amphipleura rutilans (Trentepohl) Cl. 78 ANOMOEONEIS 12 Anomoeoneis serians (Bréb.) Cl. 80 13 Anomoeoneis serians forma minor 80 14 Anomoeoneis follis (Ehr.) Cl. 80 TRACHYNEIS 15 Trachyneis aspera var. intermedia Grun. 70 MASTOGLOIA 16 Mastogloia kinsmanii Lewis 87 17 Mastogloia angulata Lewis 87 18 Mastogloia lanceolata Thwaites 87