THE MICROSCOPE IN HISTOLOGY AND BOTANY. 143 



angles so as to form a zigzag chain; striae continuous; 

 aquatic and marine. 



8. Asterionella. Fr. adherent by adjacent angles into 

 a star-like filament; v. inflated at one or both ends; 

 aquatic. 



9. Fragillaria. Fr. linear, united into a straight, close 

 filament ; striae granular, faint ; aquatic and marine. 



10. Denticula. Fr. linear, simple, or binate, rarely more 

 united; striae continuous; aquatic. 



11. Odontidium. As Denticula, but fr. forming a close 

 filament ; aquatic and marine. 



COHORT 4. MELOSIRE^:. Fr. cylindrical, disk-shaped or 

 globose; v. punctate, or often with radiate continuous 

 or granular striae. 



12. Cydotdla. Fr. disk-shaped, mostly solitary; v. 

 with radiate marginal striae ; aquatic. 



13. Melosira. Fr. cylindrical or spherical, united into 

 a filament; v. punctate, or with marginal radiate granu- 

 lar striae ; aquatic and marine. 



14. Podosim. Fr. united in small numbers, cylindrical 

 or spherical, fixed by a terminal stalk; v. hemispherical, 

 punctate; marine. 



15. Mastogonia. Fr. single; v. unequal, angular, mam- 

 miform, circular at base, without umbilical processes ; 

 angles radiating; fossil. 



16. Pododiscus. Fr. single or united, with a marginal 

 stalk ; v. circular, convex. 



17. Pyxidicula. Fr. single or binate, free or sessile ; 

 v. convex ; aquatic and marine. 



18. Stephanodiscus. Fr. single, disk-shaped; v. circu- 

 lar, equal, punctate, or striate, with a fringe of minute 

 marginal teeth ; aquatic. 



19. Stephanogonia. Fr. as in Mastogonia, but ends of 

 valves truncate, angular, and spinous; fossil. 



20. Hercotheca. Fr. single, turgid laterally ; v. with 

 marginal free setae. 



