BRITISH DIATOMACE/E. 43 



Ceratoneis Closterium, Kiitz. Bacill. iv. 11. Elir. in Prit. Anim. xv, 59. 

 Marine and brackish water. Hove, Sussex, May 1851, W. Sm. 

 Plate XV. 120. 



21. Nitzschia reversa, n. sp. F. V. lanceolate ; extremities produced 

 into beaks which are bent in contrary directions; striae 48 in 

 •OOl"; puncta obsolete, v.v. 



Brackish water. Near Lewes, Nov. 1851, W. Sm. 

 Plate XV. 121. 



22. KTitzschia acicularis, TV. Sm. F. V. lanceolate, extremities 

 produced, beaks straight ; V. faintly striated ; striee 98 in '001". 

 v.v. 



Synedra acicularis, Kiitz. Bacill. iv. 3. 



Fresh water. Near Lewes, May 1852, W. Sm. 

 Plate XV. 122. 



23. Nitzschia T^nia, W. Sm. F. V. linear-lanceolate, occasionally 

 sigmoid, extremities produced ; beaks direct or curved ; V. striated, 

 striae 72 in "001" ; endochrome in dry frustule apparently arranged 

 in a spiral manner, v.v. 



Ceratoneis gracilis, Breb. in Kiitz. Sp. Alg. p. 89. ad specim. quae communi- 

 cavit cl. De Brebisson, Oct. 1852. 



Brackish water. Near Lewes, Sept. 1851, W. Sm. Braunton, Devonshire, 

 Mr. Ralfs, Oct. 1849. 



Plate XV. 123. 



Genus 17. AMPHIPRORA, Ehr. 



Frustules free, elliptical, constricted ; valves convex, keeled ; keel 

 central, with a longitudinal line, and nodules at centre and ex- 

 tremities. 



The very peculiar frustules of this genus cannot be confounded 

 with any others, save with those of the fifth section of the last genus, 

 and from these they are usually distinguished without much difficulty. 



