BRITISH DIATOMACE/E. 53 



32. Navicula tumida, n. sp. V. elliptical, contracted at the ex- 

 tremities, which are rounded and produced ; striae very distinct, 

 24 in '001", reaching central line, punctate and radiate, v.s. 



Fresh water. Bramley near Guildford, Mr. Capron, Nov, 1850. 

 Plate XVII. 146. 



33. NavicTxla dicephala, Kiitz. V. linear, constricted towards the 

 rounded extremities ; striae distinct, 26 in "001", radiate, v.s. 



Kiitz. Bacill. xxviii. 60 ? 



Fresh water. Guildford, Mr. Capron. Lough Mourne Deposit. 

 Plate XVII. 157. 



34. Navicula cryptocephala, Kiitz. V. minute, constricted to- 

 wards the obtuse extremities; striae faint, 56 in 'OOl". v. v. 



Kiitz. Bacill. iii. 20 & 26. 



Freshwater streams. Corfe Castle, Dec. 1849, W. Sm. Belfast, Dr. Dickie. 

 Plate XVII. 155. 



Sect. VI. Valves with a central constriction. 



35. Navicula didyma, KUtz. V. elliptical, more or less deeply con- 

 stricted in the centre; striae interrupted, distinct, 24 in 'OOl". 

 Length -0014" to -0032". v.v. 



Kiitz. Bacill. iv. 7. xxviii. 7o. Navicula interrupta, Kiitz. Bacill. xxix. 93. 

 Pinnularia Apis, Ehr. in Kiitz. Bacill. xxviii. 7^. 



Marine: very common. Sussex, July 1850, W. Sm. (New Zealand.) 



Plate XVII. 154. a. and a', ordinary forms ; b. outline of ditto in S. D. ; 

 a*, var. (Sporangial ?) from Skye, Prof. Williamson. Frustule with endo- 

 chrome. Frontispiece, fig. CLIV. 



36. Navicula binodis, Ehr. V. constricted in the centre, extremities 

 slightly produced ; striae obscure, v.s. 



Kiitz. Bacill. iii. 35. 



Fresh water. Lewes, Aug. 1850, W. Sm. 

 Plate XVII. 159. 



