KONGL. SV. VET. AKADEMIENS IIANDLINGAU. 



HANI) 



27. 



n:o 



3. 



125 



Subgenus Oxyamphora. 



Frustule usually broadly elliptical, with truiu-ate ends and complex connecting 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 valve. Structure of the dorsal side: nsually fine puncta, arranged in 

 parallel, or slightly radiate, transverse strire, and in undulating, longitudiiuil lines. Ventral side 

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



A. hyaJina with cell-contents, frustule 

 in zonal view, in state of division, and 

 in valvular view; (iOO times magnified. 



A. ostrearia with cell-contents ; 

 600 times magnified. 



\ 



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

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

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

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

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

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

 ing, the plate and terminal elaeoplasts 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. qnudrata 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. 



Tliis subgenus comprises a number of forms with or without ^^- V^drata with cell-contents; 



y ^ bOO times magnified. 



stauros, which m other respects are too closely connected to be placed 



in different sections. From the subgenus Ambhjaniphora they differ by the very narrow ventral 

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

 respond to Stauroneis and Libellus. 



Artificial key. 



j Zone with some few inordinate stigmas A. magnifica Grev. 



\ — without — — — 2. 



j Without stauros 3. 



\ With — 10. 



j Thin and membranaceous 4. 



I Silicious 6. 



