KONGL. SV. VliT. AKADEMIENS HANDLINGAK. BAND 27. N:0 3. 101 



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



with a more or less distinct, blank, narrow band across the striae, in some without any keel or 



longitudinal band. Structure: usually rows of coarse puncta or strong, 



transverse costae crossed by longitudinal costse, producing a network of 



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



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



rarely without striae, frequently with short, radiate striae. 



The living cell is known in few forms only. A. 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- . _ . . , „ , , 

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

 (Pfitzbr Ban and Entw. p. 82 PI. IV f. 8, 9). A. Proteus has also a **"«« magnified, 



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

 towards the dorsal side. — On conjugating, two frustules form two auxospores, the longitudinal axis 

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

 XVII 1856 p. 2 PI. I f. 13 to 20. Borscow Sttssw. Bac. p. Ill PL 13 f. 2 a to ^ 1873). 



Artificial Icei/. 



I Very small forms. L. 0,006 to 0,oi mm. . . . . A. perpusilla Grun. 

 1. < Length 0,02 to 0,04 mm 2. 



[ — more than 0,04 mm ... 4. 



a j Ventral side not striate . . . . . . ■ A. hehringensis Cl. 



' \ — — striate 3. 



( Central area distinct A. ovalis var. Pediculus. 



■ \ — — indistinct A. Pusio Cl. 



. ( Prnstule rather rectangular 5. 



' \ — — elliptical 7. 



_ ( Ventral side striate in its whole length 6, 



\ — — — at the ends only -A. Weinekii Jan. 



I Longitudinal line distinct . . A. javanica A. S. 



( — — indistinct A. arenicola Geun. 



_ j Dorsal side longitudinally angularly bent A. dubia A. S. 



7- _ _ not - - - 8- 



Median line on an elevated keel . A. Schmidtii Geun. 



„ j Medii 



■ I — — not very elevated 9- 



( Longitudinal line on the dorsal side distinct 10. 



^- \ - - - _ _ not - 13. 



,. ( Striffi (or costs) 4 in 0,oi mm, . . . A. nodosa Br. 



10- ■} _ _ 6 to 7 - - 11. 



J Central area large A. Oculus A. S. 



' \ — — indistinct 12- 



I Ventral side throughout striate . . ... ... .A. mexicana A. S. 



■^'^' \ _ — striate along the median line and at the ends ... -A. gigantea Grun. 



I Stria 6 to 7 in 0,oi mm 14. 



'"*■ 1 - 10 to 14 - - . . 15- 



J Ventral side striate . . A. robusta Gkbg. 



14- S jjot ... ^- valida Pee. 



., , ( Ventral side striate l"- 



15- i _ —not — 4- Ovum Cl. 



17 

 ( Marine species ^'■ 



\ Fresh water — ^- ovalis KiJTZ. 



( Strise on the ventral side crossed by a blank line . . . . -A. Proteus Geeg. 



I _ _ _ _ not — — — — ^. marina V. H. {A. Proteus v. contigua). 



17 



