162 



NAVICULA. 



GENUS 7. NAVICULA BORY, 1822. 

 Frustules free or enclosed in tubes, rarely united in a chain. Valve 

 with three nodules in a straight line ; raphe straight. 



. Endochrome divided into two layers, resting on each of the sides 

 of the zone, with two lines of separation on the valves. 



^,J\ 



-JEE 



Fig. 32. Navicula 

 Lyra Ehr 



Fig. 31. Navicula 



nobilis Ehr. 



The figures here given are two type forms of Navicula : the N. nobilis and 

 the N. lyra. In the Monograph, in course of publication by Prof. 

 Cleve, descriptions of all known forms of this immense genus will be found. 

 Mr. Cleve has subdivided it into various sub-genera. As the groups which we 

 proposed in our Synopsis are very convenient for determination, and have also 

 been adopted in some important works, including the Sylloge of Prof. De 

 Toni, we prefer to retain them here. 



