242 



BOTANY. 



Fossil ZygOSporeae. Comparatively few species of Zygosporeae 

 occur in a fossil state. Tlie oldest known is a Jurassic species of Con- 

 fervites, 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. 



ARRANGEMENT OF THE CLASSES AND ORDERS OF ZYQOSPORE^B. 



CONJUGATE. 



ZOOSPORB^C. 



