KONGL. SV. VET. AKADEMIENS IIANDUNGAU. BAND 26. N:0 2. 1 1 



. ( Valve witli lateral areas iiiutiiig with the central area Nav. lijrat(e {Anomoeoncin partim). 



' ' 1 — without — — — — ■ ... '21. 



^ j I'uiicta arranged in decussating rows Xar. decussatos (A7io))ioeoneis partim). 



" \ — -- transverse strijB 22. 



I 



25. I 



jj^j . StrisB minutely and transversely lineate 23. 



punctata! — - — 24. 



„.- I Central nodule elongated • .... Brehissonia. 



~ \ — not — Nav. lineolatoc. 



„, ) I'uncta arranged in longitudinal, almost straight rows 25. 



~ ( — - — — — undulating rows 28. 



Median line between siliceous ribs 26. 



not — — — Xav. orfhosticJicc (Nav. Jusiforntcs i>artim). 



„,. I Punctation coarse Cistula. 



^•^^ 1 - fine 27. 



f t'entral nodule uniting with the ribs in a very elongated axial costa .... Atnphipleiira. 

 27. I Central nodule not uniting with tlie ribs or uniting for a short way only .... Frustulia 



I {Nar. ortlwstichoe partim). 

 •>c I '^'■'■i* distinctly punctate 29. 



\ — indistinctly or very finely punctate 32. 



^„ ( Puncta coarse Nav. punctatce. 



~'\ — small 30. 



,,„ j Median striae of unequal length Nav. hcterostichw. 



1 — — equal — 31. 



j Valve very convex, and carinated Tropidoneis. 



31. ■! Valve slightly convex not carinated Nav. microstigmaticcB (Nav. mesoleice and 



I Nav. entoleice partim). 



{ 



„„ (Median stri» more distant than the others Nav. decipic7ites (Nav. tnicrostifjmaticce \mrtim). 



'''^- \ - not - - - '. . . . 31 



„, j Axial area more or less lanceolate Nav. entoleia;. ' 



\ — indistinct 35. 



„P I Central area large 30. 



" ' \ — indistinct 37. 



„, j Central area a transverse fascia Sfcnoneis. 



\ — quadrate or rounded Nav. mcsoleia; (Anomoeoneis jiartim). 



Broad membranaceous forms Nav., minuscnla;. 



ow — — Nav. fusi formes (Nav. microstigniaticw partim). 



Valve clavate 39. 



— not — 40. 



) Structure; transverse stria; or rows of puncta Gomplionema. 



'\ — — costa, alternating with double rows of puncta .... Goniphonei.s. 



, I Structure; decussating rows of minute puncta Toxnnidca. 



40. 



,,„ . Terminal nodules incrassate or transversely dilated Nav. bacillarcs. 



^ — not — — ' — 33. 



„_ J Broad 

 \ Narro 



38. I 



\ ■ — transverse striae or rows of puncta 41. 



i Valve not strongl}' asymmetrical Cynibella (Tropidoneis, Trachyneis, 



41. Nav. pundatcB partim). 



I — strongly asymmetrical 42. 



,„ I Median line on an elevated keel Auricula.- 



\ — not — — Amphora. 



Habitat and geographical distribution of diatoms. 



A knowledge of the habitat and the geographical distribution of the diatomacece is of great 

 importance, especially for geological researches. Fossil diatoms occur doubtless more frequently 

 in geological sti'ata than is usually believed, and may furnish the geologist with valuable evidence 

 about the qualities of the water in which the sediments were deposited, whether fresh, brackish or 



* Navicula americana. — ^ Tropidoneis partim and Amphora Schmidtii 



