DESCRIPTION 



OF 



GENERA AND SPECIES. 



DlATOMACEzE. 



Unicellular algae consisting of a frustule or silicious bivalve 

 box, pseudo-unicellular, externally covered with a more or less 

 apparent mucous envelope (called coleoderm), containing in 

 the interior of the valves a cellular membrane enclosing a 

 brownish yellow colouring matter (called endochrome). a 

 nucleus, some oil globules and colourless protoplasm. 



Diatoms multiply by gemmiparous self-division and are 

 reproduced by conjugation. 



The family of Diatomaceads divided into three sub-families: 



i. Raphidieae having a true raphe on at least one of the 

 two valves. 



2. Pseudo-Raphidieae having, on at least one of the 

 valves, a blank space, simulating a raphe, and never furnished 

 with either teeth, awns, spines, or processes. 



3. Crypto-Raphidiese never possessing either a true 

 raphe or a pseudo-raphe on the valves ; generally circular, 

 sub-circular or angular in form, and frequently furnished with 

 processes, teeth, spines, or awns. 



