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



J Median oblique stria more distant than the others • • • 17. 



\ _ _ _ not 18. 



I Valve linear-lanceolate . . ■ • ■ • -P- austraU Grun. 



\ — lanceolate P. Normanii Half. 



{Transverse and oblique striai equidistant . ... 19- 

 — striffl closer than the oblique 21. 

 — — more distant — 24. 



I Valve narrow P. delicatulum W. Sm. 



\ — broad 20. 



f Strise 28 in 0,oi mm P. javaniewm Gbun. 



16. 

 17, 



19, 



' ) — 18 to 22 — P. angulatwm Qubk. 



„,. j Oblique striae at an angle of 90° 22. 



■ \ — — — about 60° P. elongatvim W. Sm. 



„- I Ends with a lunate mark P. IcergvMense' Gbtjn. 



\ — without — 23. 



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



' \ — — excentric P. subrigidum, Gbun. 



„. fEnds obtuse 25. 



' \ — acute 28. 



np. ) Valve large, about 0,3 mm. in length 26. 



\ — small — 0,1 — or less 27. 



„„ I Valve straight P. rigidum W. Sm. 



\ — sigmoid P. prcdongum Cl. 



„_ ( Transverse strise 24 in 0,oi mm P. salinarum Grttn. 



■ \ — — 27 — P. minwtum Grun. 



„„ / Valve linear, strongly sigmoid at the ends P. Brunii Cl. 



\ — lanceolate — — — 29. 



„. J Transverse strise 17 in 0,0 1 mm P. Grundleri Grun. 



t — — 21 to 24 — P. Stuxbergii Cl. «,. Gb. 



„. f Median line ilexuose P. incertum Per. (P. falcatum Done). 



<*»• \ _ _ not 31. 



„ I Median line enclosed between longitudinal lines P. Exul Cl. 



^^- ^ - not - - - 32. 



32. 



34. {^^1- 



Central area large P. umbilicatum Cl. 



small or indistinct ■ 33. 



„„ (Oblique strise at an angle of 90° 34. 



■ t — _ — _ less than 90° 37. 



: Valve broad, lanceolate 35. 



narrow, linear-lanceolate 36. 



„. ( Median oblique striae more obtuse than the others P. majus Gbun. 



' I — — — not — — P. Reros Cl. 



.,„ ( Frustule arcuate P. Weissflogii Gbun. (P. formosum var. Arcus). 



\ — not P. formosum W. Sm. 



„„ j Valve linear 38. 



' ■ \ — lanceolate 40. 



„„ f Valve carinated P. carinatum Done. 



^"- i - not 39. 



/ Median line strongly excentric P. obscurum W. Sm. 



„ / Median line 



f Ends subrostrate P. JBstuarii BrSb. 



^- \ - not 41. 



... f Valve rhomboidal 43. 



\ — narrow lanceolate 43, 



.g ) Transverse strise about 17 in 0,oi mm p, rhombeum Grun. 



■ I — — — 24 — P. latum Cl. 



^g f Striae about 22 in O.oi mm p. acutum Nobm. 



I — 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. O.oie to 0,02 mm. Median line straight, ,central. Transverse and 



