96 



TERMINOLOGY AND CLASSIFICATION OF DIATOMS. 



FAMILY (III.) NAVICULACE^E. 



Frustules with similar f Valves elliptic with a projecting keel . 

 valves, asymmetrical - ..... , , , 



about both axes I Valves sigmoid, without keels or alas 



Fiustules with similar f 

 valves, symmetrical -l Valves naviculoid, without keels or a.\x. 

 about both axes . L 



Frustules with similar f Valves elliptic, with marginal aloe and 

 valves, symmetrical i robust costaa .... 

 about the major axis . j^ Valves linear, without alas or keels 



Frustules with similar f 

 valves, symmetrical 4 Valves arcuate .... 



about the minor axis . (.. 



Tribes. 



5. Amphiprorese. 



6. Pleurosigmeae. 



7. Naviculese. 



8. Surirellese. 



9. Synedrese. 



10. Eunotieae. 



Sub-Order (B.) COCCOCHROME^E. 

 Family (IV.) TABELLARIACE/E. 



Frustules rectangular f Frustules rectangular. Valve view gener- 

 or cuneate, furnished | a n y elliptic, never cuneate 

 with diaphragms or A , 



semi-diaphragms par- Frustules and valves cuneate, valve view 

 allel to' the valves . I cuneate ..... 



Frustules cylindrical, consisting of plates united by their margins and 

 terminating in conical or pointed valves .... 



11. Tatoellarieae. 



12. Licmophoreae. 



13. Rhizosoleniese. 



Family (V.) FRAGILARIACLE. 



Valves linear, elliptic, constricted or sometimes cuneate; striate' 

 transversely, without nodules or raphe .... 



Valves elliptic, punctated with coarse puncta, often quadrate with 

 hyaline spaces at the centre and apices .... 



Valves always cuneate with coarse puncta, often quadrate or with slits 

 like buttonholes. No hyaline space at the centre . 



14. Fragilariese. 



il. Plagiogrammeae. 



16. Trachysphenieae. 



Family (VI.) CH.ETGvRACE/E. 

 Valves rounded or elliptic, furnished with long filaments 



17. Chsetocerese. 



Family (VII.) BIDDULPHIACE.E. 



Valves polymorphous, triangular, quadrate, polygonal, sometimes 

 elliptic, never discoid, often furnished with spines . 



18. Biddulphiese. 



Family (VIII.) COSCINODISCACE^E 



Valves discoid, sometimes elliptic, furnished with one or more marginal 

 ocelli or projecting tubercular processes .... 



Valves discoid, divided (following the course of the radii) into sections 

 alternately light and dark ...... 



Valves discoid with a central hyaline area connected by hyaline furrows 

 to marginal ornate compartments ..... 



Valves discoid, sometimes elliptic, with surface covered with areoles of 

 beads arranged in lines radiate, transverse or vertical, or well 

 divided in concentric zones with different markings 



19. Eupodiscese. 



20. Heliopeltese. 



21. Asterolamprese. 



22. Coscinodiscese. 



Family (IX.) MELOSI RACEME. 



Valves discoid, very convex, furnished with marginal spines. Frustules 

 globose ........ 



Valves discoid, flat or slightly convex, sometimes furnished with small 

 spines on the surface. Frustules cylindrical, often united into 

 cylindrical filaments . ..... 



23. Xanttaopyxideae. 



24. Melosirese. 



