KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 27. NtO 3. 101 



valve in some species with a keel at a longer or shorter distance. from the median liiie, in some 



with a more or less distinct, blank, narrow band across the stritB, in some witliout any keel or 



longitiidinal band. Structnre: usnally rows of coarse puncta or strong, 



transverse costEe crossed by longitiidinal costfe, producing a network of 



more or less regular quadrate alveoli. Ventral part of tbe valve without 



a keel, but in some cases with a narrow blank band across the stricB, 



rarely withont strige, frequently with short, radiate striee. 



The living cell is known in few forms only. Ä. ovalis, contains a 

 single chromatophore-plate along the ventral side of the zone and the 

 inside of the valves. At the end of the ventral side it has a broad and 

 deep sinus. It has also a narrow and deep sinus from the margin to- , „ , 



jA rfotplf^ "witli fpl 1 -flin f pni"^ 



wards the central nodule. Central plasma-mass and nuclens distinct (ventral and dorsal side) 600 

 (Pfitzer Bau and Entw. p. 82 Pl. IV f. 8, 9). A. Proteus has also a t^^^^ magnified. 



single chromatophore-plate along the ventral side of the zone and extending along the valves 

 towards the dorsal side. — On conjugating, two frustnles form two auxospores, the longitndinal axis 

 of which crosses the longitndinal axis of the mothercells (Cärter, Ann. a. Mag. Nat. Hist. 2 ser. 

 XVII 1856 p. 2 Pl. I f. 13 to 20. Borscow Siissw. Bac. p. 111 Pl. 13 f. 2 a to ^ 1873). 



Artificial ket/. 



i Very small forms. h. 0,006 to 0,oi mm A. perpusilla Gbun. 



1. ! Length 0,o2 to 0,04 mm 2. 



I — more than 0,04 mm 4. 



g j Ventral side not striate A. behringensis Cl. 



^1 — — striate 3. 



„ ( Central area distinct A. ovalis var. Pedicuhis. 



' \ — — indistinct A. Pusio Cl. 



Frustnle rather rectangular 5. 



— — elliptical 7. 



^ I Ventral side striate in its whole length 6 



'■{ 



^ i Longitndinal line distinct A. javanica Ä. S. 



I — — indistinct A. arenicola Grun. 



- j Dorsal side longitudinally angularly bent Ä. dubia Å. S. 



■ I — — not — — — 8. 



„ J Median line on an elevated keel A. Schmidtii Gkun. 



I — — not very elevated 9. 



q ) Longitndinal line on the dorsal side distinct 10. 



I - - - - - not - 13. 



.., J Striae (or costse) 4 in 0,oi mm ^4. nodosa Br. 



t - - 6 to 7 - - 11. 



... 1 Central area large A. Oculus A. S. 



' \ — — indistinct 12. 



..„ i Ventral side thronghout striate A. mexicana A. S. 



1 — — striate along the median line and at the ends A. gigantea Gbun. 



.„ I Strise 6 to 7 in 0,oi mm 14. 



1 — 10 to 14 — - 15. 



.., I Ventral side striate A. robusta Grbg. 



' \ — — not — A. valida Per. 



..p. ( Ventral side striate 16. 



■ \ — — not — A. Ovitm Cl. 



..„ I Marine species 17. 



\ Fresh water — ' A. ovalis KtJTZ. 



.._ i Striae on the ventral side crossed by a blank line A. Proteus Greg. 



' \ — - — — — not — — — — A. marina V. H. (A. Proteus v. contigua). 



