KONGL. 8V. VKT. AKADEMIKNS HANDLINGAlt. BANJ) 27. N:<» 3. 101 



valve in some species with a keel at a l()iif>'('i' or shorter distance from the median line, in some 



with a more oi' less distinct, blank, narrow l)atHl across the stria", in some without any keel or 



longitudinal hand. Structure: usually rows of coarse j)Uiicta or strong, 



transverse costjie crossed by longitudinal costrc, 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 strife, 



rarely without striee, frequently with short, radiate striaj. 



The living cell is known in few forms only. A. oiHiiis, contains a 



single chromatophore-plate along the venti'al 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- , ^, , . , ,, ^ , 



' 111 /-I 11 !• • •'^- "^'ofeus with rell-content.s 



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



(Pfitzer Ban and Entw. p. 82 PI. IV f. 8, 9). A. Frofeus 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 185(5 p. 2 PI. I f. 13 to 20. EoRSCOW Slissw. Bac. p. Ill PI. 13 f. 2 « to ^ 1873). 



Artificial kei/. 



[ Very small forms. L. 0,006 to 0,<m mm .-1. jx^rpiisilla Grcn. 



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



— more than 0,04 mm 4. 



^ . Ventral side not striate A. behringensis Cl. 



— striate 3. 



) Central area distinct A. ovalis var. Pediculus. 



' \ — — indistinct A. Pusio Cl. 



, j Prustule rather rectangular 5. 



1 — — elliptical 7. 



, j Ventral side striate in its whole length (3. 



" ' \ — — — at the ends only A. Weinekii Jan. 



. ( Longitudinal line distinct A. javanica A. S. 



'■ I — — indistinct A. arenicola Grun. 



„ ( Dorsal side longitudinallj' angularly bent A. dubia A. S. 



' \ — — not — — — 8. 



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



( — — not very elevated 9. 



j Longitudinal line on the dorsal side distinct 10. 



■'• ) - - - - - not - 13. 



j Striae (or costa;) 4 in 0,oi mm A. nodosa Br. 



^"- \ - _ 6 to 7 - - 11. 



. I Central area large A. Ocnlus A. S. 



' \ — — indistinct 12. 



J Ventral side throughout striate A. mexicana A S. 



\ — — striate along the median line and at the ends A. gigantea Grun. 



,„ J Strise 6 to 7 in 0,oi mm 14. 



'^- 1 - 10 to 14 - - 15. 



f Ventral side striate ^4. robusta Greg. 



■ \ — — not — A. valida Per. 



... ( Ventral side striate I*''- 



■'■^- \ _ _ not — A. Ovum Cl. 



^„ j Marine species 17- 



\ Fresh water — ^ ovalis KtJTZ. 



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



\ _ -^ — ^ not — — — • — A. marina V. H. (.4. Proteus v. contigua). 



