25. {'' 



KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 26. N:0 2. 11 



q. I Valve with lateral areas unitiug witli tbe central area Nav. lyratcc (Anomoeoneis partim). 



■" ■ i ^ without — — — — . , . ; ■ ... 21. 



Q.. I Pancta arranged in decussating rows Nav. deciissatw (Anomoeoneis partim). 



"1 — — transverse striae 22. 



Q„ I StrifB minately and transverselj' lineate 23. 



" ' I — punctatse — - — 24. 



„„ ) Central nodule elongated ■ .... Brebissonia. 



\ — not — Nav. lineolatm. 



g, ) Puncta an'anged in longitudinal, almost straight rows 25. 



\ — — — — undulatlng rows 28. 



Median line between siliceous ribs 26. 



not — — — Nav. orthostichce (Nav. fusiformes partim). 



„„ I Punctation coarse Cistula. 



^^- \ - tine 27. 



f Central nodule uniting with the ribs in a very elongated axial costa .... Amphipleiira. 

 27. 1 f'eutral nodule not uniting with the ribs or uniting for a short way ouly .... Frustulia 



( (Nav. ortho.stichoe partim). 

 ^„ ) Strije distinctly punctate 29. 



\ — indistinctly or very finely punetate 32. 



„„ j Puncta coarse Nav. pnnctatce. 



t — small 30. 



„„ j Median striae of unequal length Nav. heterostichce. 



y — — equal — •. . 31. 



( Valve very convex, and carinated Tropidoneis. 



31. •! Valve slightly convex not carinated Nav. nncrostigmaticas (Nav. mesoleice and 



I Nav. entoleicB partim). 

 „ J Terminal nodules incrassate or träns versely dilated Nav. bacillares. 



\ — not — — — 33. 



„„ ( Median striae more distant than the others Nav. decipientes (Nav. microstigmaticcB partim). 



''•^- t - Dot - - - 34. 



„ , ) Axial area more or less lanceolate N^av. entoleia: ' 



1 — indistinct 35. 



I Central area large 36. 



' ' \ — indistinct _ 37. 



„„ ( Central area a transverse fascia Stcnoneis. 



öfa. 



= r 



quadrate or rounded Nav. niesoleim (Anomoeoneis partim). 



, Broad niembranaceous forms Nav. niinwsculce. 



3i. 



- I B 



' u 



arrow — — Nav. fusiformes (Nav. microstigmaticoe partim). 



„„ ) Valve clavate 39. 



*• 1 — not - 40. 



„„ ( Structure: transverse striae or rows of puncta Gomphonema. 



\ — — costae, alternating with double rows of puncta .... Gornpiwneis. 



I Structure: decussating rows of minute puncta Toxonidea. 



\ — transverse stria or rows of puncta 41. 



[ Valve not strongly asyrametrical Cynibella (Tropidoneis, Trachyneis, 



41. I Nav. punctatm partim). 



( — strongly asymmetrical 42. 



, Median line on an elevated keel Auricida. ^ 



not — — Amphora. 



J Median 



Habitat and geographical distribution of diatoms. 



A kiiowledge of the liabitat and the geographical distribution of the diatomacece is of great 

 importance, especially for geologieal researches. Fossil diatoms occur dottbtless more freqitently 

 in geologieal strata than is usually believed, and may furiiish the geologist with valuable evidence 

 aboiit the qnalities of the water in which the sediments were deposited, whether fresh, brackish or 



Navicula americana. — ' Tropidoneis partim and Amphora Schmidtii 



