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



16, 

 17. 

 18. 

 19. 



J Costae inorassate ai, the margin D. Adonis Brun. 



\ — not — — 17. 



J Segments almost orbicular D. interrupta Kutz. 



\ — elongate-elliptical . . . D. Guinardiana Brun. 



( Valve not constricted 19. 



\ — pandnriform 23. 



{Valve very convex and thick . . . . D. circumnodosa Brdn. 

 — not — — 20. 



„., I Valve elliptical D. Cynthia A. S. 



) — linear 21. 



„.. I Furrows decreasing in breadth from the middle '. D. nmnda Jan. 



' I — of equal breadth throughout 22. 



„, J Central nodule small ,., ,. D. mediterranea Geun. 



( — — large . D. contigua A. S. 



„„ J Furrow crossed by costse D. Letourneiirnii Cl. 



I — without or with rudimentary costse 24. 



f Costse 4 to 7 in 0,oi mm. . . . . .' , . . D. muscce/ormis Grun. 



24. ■! — 7 to 8 — .... jD. constricta Geun. 



[ — 11 to 12. — D. incurvata Greg. 



f CostsB crossed by a single longitudinal rib 26. 



25. •! — — several — ribs 35. 



[ — alternating with double rows of alveoli 61. 



I Valve nut constricted ... . . .... . 27. 



\ — constricted . 29. 



J L. 0,02 to 0,03 mm . . 28. 



\ L. 0,04 to 0,08 mm D. lineata Donk. 



{Furrows broad D. discrepans A. S. 

 — narrow . . . D. Papula A. S. 



{Valve gently constricted . . . 30. 

 — deeply — . . . 34. 



{Furrows decreasing in breadth irom the middle . . . . . D. Vetula A. S. 



— • of almost equal breadth . . . . ... .... 31. 



j Furrows very broad .... . . D. binaria A. S. 



\ — not — . .... 32. 



I Longitudinal rib in the middle of the striae 33. 



\ — — marginal . . D. siibcineta A. S. 



I Rib narrow ... . . . D. exemta A. S. 



\ — broad . D. demta A. S. 



{L. about 0,03 mm D. bombiformis Cl. 

 L. 0,07 to 0,1 mm .... D. coarctata A. S. 



I Valve constricted , 36. 



I — not - 50. 



,,„ I Valve with ocelli . . . . D. areolata Cl. 



t — without 37. 



„, j Valve strongly constricted , 38, 



I — slightly — 45. 



qo ( Segments orbicular D. Clepsydra Cl. 



\ — elliptical or deltoid 39. 



„„ I CostsB alternating with faint alveoli D. Prcestes A. S. 



\ — — — distinct — 40. 



26 

 27, 

 28, 

 29 

 30 

 31 

 32, 

 33, 

 34, 

 35, 



40. 

 41. 

 42. 

 43. 



44. 



{Ribs forming undulating rows D. splendida Greg. 

 — — straight or curved ... 41. 



( L. 0,04 or less D. Griindleri A. S. 



\ L. larger .... 42. 



( Furrows indistinct D. Weissjtogii A. S. 



( — distinct 43. 



{Ribs two to Ave on each side of the median line 44. 



— eight to ten . . . . D. Kiitzingii Grck. 



( Transverse costae 5 to 8 in 0,oi ram. . . £>. Bombus Ehb. 



I — — 8 to 13 — . . D. chersonensis Grun. 



