NAVICULA. 431 



Hah. Cheshunt : A. 11. H. Aberdeen : Dr. Dickie. 

 A very well marked species. 



4. Navicula plattstoma Ehr. 

 Plate CII. Fig. 6. 



Char. Frustules elongated, quadrangular, ivith straight sides, 

 rostrated at each end. 

 Hab. Cheshunt: A. H. H. 

 Die Infus. p. 178. t. xiii. fig. 8. 

 A distinct and not uncommon species. 



b. Frustules striated. 



5. Navicula nodosa Ehr. 



Plate CII. Fig. 7. 



Char. Frustules small, in side vieio thrice undulated, ros- 

 trated at each extremity. 



Die lufus. t. xiii. fig. 9. Frustulia nodosa ? Jenner, in 

 Fl. of Tunbridge Wells, p. 204. 



Hah. On Ashdown Forest, near Forest Kow, between 

 Gardener Street and Hailsham, &c. : Mr. Jenner. 



Mr. Jenner remarks that his specimens agree with Ehren- 

 berg's description and figures in every respect save that the 

 frustules were striated. It is probable that Ehrcnberg 

 overlooked the strias, and that these are always present. 



6. Navicula injlqualis Ehr. 



Plate CII. Fig. 13. 



Char. Frustules in front view attenuated, toicards each end 

 truncate ; in side aspect unequal. 

 Navicula inaqualis, Bcricht. dcr Akademic d. Wisscnsch. 

 zu Berlin, 1836, p. 53. ; Die Infus. p. 184. t. xiii. f. 18. 



