EUASTRUM. 6 



/3. Cells of medium size (length 26 135 /u), polar lobe 

 distinctly elongate ; cell- wall smooth or scrobicu- 

 late ; external angles of polar lobe rounded. 



17. E, insigne. 



18. E. intermedium. 



19. E. Webbianum. 



y. Cells generally small (length 10 79^); cell-wall 

 smooth, granulate, or spinous ; external angles of 

 polar lobe usually furnished with a spine. 



* Lateral margins creuate, lobed, or sinuate. 



t Margins crenate. 



20. E. Sendtnerianum. 

 ft Margins lobed or sinuate. 



21. E. rostratum. 



22. E. Turnerii. 



23. E. spinosum. 



24. E. bidentatum. 



25. E. pictum. 



26. E. divaricatum. 



27. E. dubium. 



28. E. erosum. 

 ** Lateral margins usually without lobes. 



29. E. pulcliellmn. 



30. E. elegans. 



31. E. Unale. 



32. E. denticulatum. 



33. E. minutiasimum. 



34. E. incavatum. 



35. E. montanum. 



SECTION B. Polar lobe entire, generally somewhat retuse in the 

 middle. 



a. Cells large, 48 114 /u in length. 



* Margin distinctly lobed. 



f Cell-wall smooth. 



36. E. pectinaium. 

 tt Cell- wall granulate. 



37. E. gemmatum. 



38. E. verrucosum. 

 ** Margin not lobed ; cell- wall granulate. 



39. E. occidental, 

 p. Cells small, 17'5 48 ^ in length. 



* Seinicells distinctly three-lobed. 



40. E. insulare. 



41. E. crassangulatum . 



42. E. Cornubiense. 

 ** Seinicells not distinctly three-lobed. 



43. E. crassicolle. 



44. E. crispulum. 



45. E. snblobatum. 



46. E. validum. 



