342 



BOTANY. 



Fossil Zygosporese.— Comparatively few species of Zygosporeae 

 occur in a fossil state. Tlie oldest known is a Jurassic species of 0(m- 

 feroites, a genus which is also represented by a few species in the Ter- 

 tiary. Fossil Diatoms of many species have been found in the Tertiary ; 

 at Richmond, Va., they form a vast bed, nearly ten metres thick, and 

 one at Monterey, California, is sixteen metres in thickness. 



Akrangbment of the Classes and Orders of Zygospores. 



S 



a 



o 



•a 

 a 

 a 



Conjugate. 



Z00SF0BE.S^ 



