230 



DISCOVERY REPORTS 



12. 



12. 



J 3- 



13. 



14. 



14. 



IS- 

 15- 



16. 

 16. 



i7- 

 i7- 

 18. 

 18. 

 19. 

 19. 

 20. 

 20. 

 21. 



21. 



22. 

 22. 



23- 

 23- 

 24. 

 24. 



25- 



25- 

 26. 

 26. 

 27. 

 27. 

 28. 

 28. 

 29. 

 29. 



3°- 

 3°- 



3 1 - 

 3 1 - 



32- 

 32- 



33- 

 33' 



Spines minute 



Spines not shorter than half the pervalvar axis 



Valves with central spine 



Central spine absent 



Valve surface coarsely areolate ... 



Valve surface hyaline 



Valves punctate, radially furrowed 



Valves hyaline 



Valves with a corona of marginal spinulae 



Marginal processes one or two only 



Marginal process one only, reduced to an apicule 



Marginal processes two, each bearing a small mucro... 



Cells with extra-valvar radial extensions 



Cells without radial extensions ... 



Valve surface areolate, extensions loculate 



Valve surface hyaline, extensions spinous 



Valves of each cell differing from one another 



Cells with similar valves... 



Valve surface punctate, irregularly fasciculate . . . 



J 3 



H 



.. Schroderella (241) 



Detonula (*) 



Stephanopyxis (236) 



. . Skeletonema (236) 



Melosira (234) 



16 



Bacteriosira (*) 



17 



Lauderia (240) 

 .. Cerataulina (279) 



19 



20 



Planktoniella (257) 



Gossleriella (258) 



... 21 



... 22 



Schimperiella (256) 



Valve with 6-10 punctate radial lines in each quadrant; other radial lines fine and 



Charcotia (256) 

 Actinocyclus (259) 



23 



Hyalodiscus (235) 



24 



numerous ... 



Valves each with a small marginal ocellus 



Valves without a marginal ocellus 



Valves differentiated into two concentric zones by the scar of abscission 



Valve surface not divided into zones 



Pervalvar axis less than the diameter of the valve, areolation usually coarse... Coscinodiscus (242) 

 Pervalvar axis greater than the diameter of the valve, areolation extremely fine 



Ethmodiscus (255) 



Cells cuneate in girdle view, segmental in valve view, valve surface punctate 



Hemidiscus (264) 

 Cells not cuneate in girdle view, or segmental in valve view 



Cells tubular 



Cells gonioid, angles produced, or differentiated 



Cells with conical valves... 



Cells with flat or weakly convex valves 



Valves with marginal corona of bristles 

 Valves without corona of bristles 



Bristles bifurcate ... 



Bristles not bifurcate 



Intercalary bands of connective zone spirally arranged 



Intercalary bands of zone not spirally arranged 



Valves with marginal corona of small spines ... 



Valves without corona of spines... 



Valves flat with marginal spur 



Valves convex, marginal spur absent 



Cells with two angles in valve view 



Cells with more than two angles 



* See note on page 229. 



26 



27 



33 



Rhizosolenia (309) 

 ' 28 



29 



3° 



Barter iastrum (306) 



Corethron (325) 

 . Dactyliosolen (322) 



3 1 



. Schroderella (241) 

 32 



Guinardia (321) 

 Leptocylindrus (322) 



34 



39 



