130 p. T. CLEVE, SYNOPSIS OF THE NAVICULOID DIATOMS. 



Var. lineata Cl. — L. of V. 0,08 5; B. 0,oi5 mm. Striae 12 to 13 in 0,oi mm., composed of 

 puncta (about 9 in 0,oi ram.) forming straight, longitudinal rows. — A. litoralis Cl. M. D. N:o 255. 



Marine: Mouth of Somme! 



Var. minor Grun. (1880). — Frustule elliptical, truncate. L. 0,o3 to 0,o37; B. 0,oi7 to 

 0,019 mm. Divisions about 8 in 0,oi mm. Striae 17 in 0,oi mm. — A. D. p. 25. Cl. M. D. N:o 142. 



Marine: West coast of Sweden! 



Var. helgica G-eun. (1880). — Frustule rectangular. L. 0,033 to 0,048; B. 0,02i to 0,022 

 mm. Divisions of tlie zone about 9 in 0,oi mm. Striae on the zone 18 in 0,oi mm. Valve with 

 16 to 17 finely punctate striai in 0,oi mm. — V. H. Syn. p. 5fi V. H. T. N:o 74. 



Marine: Belgium! 



16. A. laevis G-reg. (1857). • — Frustule hyaline and membranaceous, rectangular, with more 

 or less truncate ends. L. 0,o4 to Odo; B. 0,o2 to 0,04 mm. Zone with numerous divisions, 6 to 

 9 in 0,01 mm. Striae fine, about 22 in 0,oi mm. — D. of Clyde p. 514 PI. XIl f. 74 o, h, c. 

 A. S. Atl. XXVI f. 10. Grtjn. A. D. p. 24 PI. I f. 8 (var of A. ostrearia?). Dannf. D. of the 

 Baltic p. 20 PI. I f. 5. 



Brackish and marine: Finmark! North Sea! Balearic Islands! Java (A. S. Atl.). 



A. Icevis difi'ers from A. ostrenria by being more transparent and thin. The striae are much 

 more delicate, and scarcely visible on the connecting zone. In some specimens the stauros is only 

 imperfectly developed, in which case A Icevis offers a remarkable likeness to A. lineolata. Akin 

 to A. Imvis is probably A. nobilis Flogel Pommerania Exp. p. 88 f. 9. 



Var. Imvissima Greg. (1857). — F. very thin. L. 0,06 to 0,07 6; B. 0,023 mm. Divisions 

 of the zone obscure. Striae 27 to 28 in 0,oi mm. -■ A. Icevissima Greg. D. of Clyde p. 513 PI XII 

 f. 72. A. S. Atl. XXVI f. 3, 13, 14. V. H. T. N:o 8. 



Brackish and marine: Sea of Kara! Finmark! Scotland! England! 



Var. minuta Cl. — Frustule in L. about O.oss; B. 0,o2 mm. Striae very delicate. — 

 A. loivissima H. L. Sm. T. N:o 615. 



Marine: Helgoland! 



Y&v. per minuta Grun. — Frustule in L. 0,ni6 to 0,oi8; B. 0,oo85 mm. Striae very delicate. 

 — A. leeviss. var. permin. Grun. in V. H. T. N:o 9. A. Mans Flogel? (Grun.). 



Marine: Swansea Docks, Schleswig (Grun.). 



To a. Icevis seems to belong A. excisa Greg. (D. of Clyde p. 521 PI. XIII f. 86, 1857) and 

 A. S. Atl. XXXIX f. 3. 



17. A. quadrata Br^b. (1889). — Frustule very thin and membranaceous, rectangular, with 

 broad, truncate ends. L. 0,09; B. 0,03 mm. Stauros narrow. Zone with numerous, strongly 

 marked divisions, about 6 in 0,oi mm. Strife exceedingly fine. — Kutz Sp. Alg. p. 94? V. H. 

 Syn. p. 56 PI. I f. 24. A. parallela Flogel Pommerania Exp. p. 88 f. 8 (1873)? A. polysonata 

 Castr. D. of Challenger Exp. p. 8 PI. XXVII f. 18 (1856)? 



Marine: Belgium (V. H.), Sweden, Fiskebackskil ! 



This species is remarkable for its cell-contents, the chromatophores being numerous rounded 

 discs, as in the coccochromatic diatoms. It differs from A. ostrearia in its rectangular outline 

 and exceedingly fine structure, and from A. Icevis in its strongly marked divisions. 



Subgenus Amblyamphora. 



Frustule more or less rectangular. Connecting zone complex. Valves linear to lunate, with 

 obtuse, usually broad ends. Components of the median line divergent towards the dorsal margin. 

 Axial and central areas indistinct. Structure: fine puncta arranged in transverser striae, which 

 on the ventral side usually diverge towards the median line. No longitudinal lines. 



