34 p. T. CLEVE, SYNOPSIS OF THE NAVICULOID DIATOMS. 



^^ I Median oblique strise more distant than the others 17. 



^^ \ - - - not , ^.18. 



,_ J Valve linear-lanceolate P. australe Grun. 



\ — lanceolate P. Normanii Ralf. 



f Transverse and oblique stria! equidistant 19. 



18. < — strise closer than the oblique -. , . 21. 



[ — - more distant — 24. 



J Valve narrow P. delicatulum W. Sm. 



\ — broad 20. 



I StriiE 28 in 0,oi mm P. javanicum Grun 



' I — 18 to 22 — P. angulatum Quek. 



I 



„^ . Oblique strise at an angle of 90° 22. 



about 60^ P. elongatuin W. Sm. 



„ j Ends with a lunate mark P. kcrgnelen.se Grun. 



\ — without — 23. 



„„ J Median line central at the ends P. longum Cl. 



28. i 



J,, j Ends obtuse 25. 



\ — acute 28. 



jj, j Valve large, about 0,3 mm. in length 26. 



"^ ' I — small — 0,1 — or less 27. 



_ J Valve straight P. rigidum W. Sm. 



\ — sigmoid P. pralongum Cl. 



„., I Transverse stria 24 in 0,oi mm P. salinaruni Grun. 



' \ — — 27 — P. minutum Grun. 



29. I 



— lanceolate — ■— — 29. 



Transverse strise 17 in 0,0 1 mm P. Griindleri Grun. 



— — 21 to 24 — P. Stuxbergii Cl. a. Gr. 



I Median line flexuose P. incertu))i Per. (P. falcatum Donk). 



\ — — not 81. 



Median line enclosed between longitudinal lines P. Exul Cl. 



{ 



J Central area large P. umbilicatum Cl. 



(Oblique strise at an angle of 90° 34. 



^^- \ not - - - 32 



^ small or indistinct 



34. I 



^^ \ - — — — less than 90° 37. 



Valve broad, lanceolate 35. 



— • narrow, linear-lanceolate 36. 



„^ I Median oblique strise more obtuse than the others P. majus Grun. 



' \ — — — not — — P. Hero.s Cl. 



. I Frustule arcuate P. Weissfiogii Grun. (P. formonum var. Arcus). 



\ — not P. formosiim W. Sm. 



Valve linear 38. 



lanceolate 40. 



„„ I Valve carinated P. carinatuni Donk. 



^^- i - not 39. 



„„ ) Median line strongly excentric P. ohscurum W. Sm. 



' \ — — excentric in the ends P. speciosicm W. Sm. 



.. i Ends subrostrate P. ^stuarii Br^b. 



^0- i - not 41. 



j Valve rhomboidal 42. 



37. I 



41. » 



narrow lanceolate 43 



.„ I Transverse stri» about 17 in 0,oi mm P. rhomheum Grun. 



' \ — — — 24 — P. latum Cl. 



.., J Strise about 22 in O.oi mm P. acutnm Norm. 



' \ — 20 — P. maroccanum Cl. 



1. P. Nubecula W. Sm. (1853). — V. narrow lanceolate, not, or slightly, sigmoid, with sub- 

 cute ends. L. 0,095 to 0,i6; B. 0,oi6 to 0,02 mm. Median line straight, central. Transverse and 



