KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 



27. 



n:o 



3. 



125 



Subgenus Oxyamphora. 



Frustiile usually broadly elliptical, with truncate ends and complex corniecting zone. Valves 

 lunate, acute. Median line approximate to the ventral margin. Central nodule transversely dilated 

 to a stauros or not. Axial and central areas usually indistinct. No longitudinal lines or keels 

 on the dorsal side of the val ve. Structure of the dorsal side: usually fine puncta, arranged in 

 parallel, or slightly radiate, transverse stripe, and in undulating, longitudinal lines. Ventral side 

 with, usually, much closer strise than the dorsal side. 



I\ 



A. hyalina with cell-contents, frustnle 

 in zonal view, in state of division, and 

 in valvular view; 600 times magnified. 



Hi: 



A. ostrearia with cell-contents ; 

 600 times magnified. 



Cell-contents. I have examined living specimens of A. hyalina, A. ostrearia and A. quadrata. 

 In A. hyalina there is, along the ventral side of the connecting zone, a flat chromatophore-plate, 

 the extremities of which are deeply indented and at the ends of which 

 a single eleeoplast constantly occurs. On the dorsal side of the plate 

 and on its centre the nucleus occurs enclosed in a plasma-mass, from 

 which radiate fine threads towards the wall of the frustule. On divid- 

 ing, the plate and terminal elseoplasts are longitudinally cloven. If the 

 living frustule be stained with methylene-blue, numerous, intensely 

 coloured granules make their appearance in the primordial stratum of 

 the plasma. A. ostrearia has two chromatophore-plates, one along the 

 dorsal wall of the connecting zone. Both are deeply constricted in the 

 middle. A. quadrata has instead of chromatophore-plates a large number 

 of small, rounded discs, gathered below the central plasma-mass and at 

 the extremities. It is thus, as to its cell-contents, a coccochromatic 

 diatom. 



This subgenus comprises a number of forms with or without 

 stauros, which in other respects are too closely connected to be piaced 

 in difPerent sections. From the subgenus Amhlyamphora they differ by the very narrow ventral 

 side and by the acute, frequently apiculate, ends of the valve. In the genus Navicula they cor- 

 respond to Stauroneis and Libellus. 



quadrata with cell-contents; 

 6tK) times magnified. 



Artificial hey. 



. ) Zone with some few inordinate stigmas A. magnifica Geev. 



) — without — — — 2. 



, j Withont stauros 3. 



^- t With - 10. 



„ j Thin and memhranaceons 4. 



I Silicions 6. 



