BRITISH DIATOMACE^. 39 



3. Nitzschia Sigma, TV. Sm. F. on F. V. linear, gradually tapering 

 towards the truncated extremities ; V. linear on F. V., somewhat 

 lanceolate, acute ; striae 56 in -OOl" ; puncta of keel in a double 

 row. Length -0050" to -0116". v.v. 



Synedra Sigma, Kiitz. Bacill. xxx. 14. 



Marine or brackish water. Pevensey Bay, Sept. 1850, W. Sm. 

 Plate XIII. 108. 



4. Nitzschia obtusa, n. sp. F. on F. V. linear, with rounded ex- 

 tremities; V. linear, obtuse ; puncta double; striae 56 in -OOl". 

 Length -0042" to -0121". v.v. 



Brackish water. Shagalieu Marsh, Poole Bay, June 1849, TF. Sm. 

 Plate XIII. 109. 



5. Nitzschia spectabilis, n. sp. F. on F. V. linear, sigmoid, trun- 

 cate ; keel nearly central ; puncta in 4 rows, the more distant on 

 each side larger ; V. striated, v.s. 



Brackish water. Near Ipswich, Mr. Hodgson, Aug. 1851. 

 Plate XIV. 116. 



Sect. IL Valves linear, straight. 



6. Nitzschia scalaris, JV. Sm. F. V. linear, inflated towards the 

 truncated extremities ; V. linear, slightly tapering towards the ex- 

 tremities, which are somewhat acute ; keel eccentric ; puncta 

 double, alternately produced into shorter and longer striae ; surface 

 of valve distinctly striated ; striae 24 in •OOl". Length '0125" to 

 •0172". v.v. 



Synedra scalaris, Kiitz. Bacill. xxviii. 32. 



Brackish water. Shagalieu Marsh, Poole Bay, June 1849, W. Sm. 

 Plate XIV. 115. Ideal section of frustule, fig. 115 s. 



7. Nitzschia linearis, TF. Sm. F. V. linear, with rounded or trun- 

 cated extremities, occasionally with a slight central constriction ; 

 V. linear, with acuminate extremities ; keel nearly central ; puncta 

 in a single row ; striae obscure. Length '0023" to "OOJS". 



Frusfulia linearis, Ag. ex sj). authen. quae misit cl. Dr. GrcviUi*. 



