RRITISII DIATOMACE.'R. 45 



transverse line ; striae faint, 68 in -001", Length -0024" to -0054". 

 v.v. 



Kiitz. Bacill. xxix. 34. Prit. Anim. xvi, 6? 



Marine and brackish water. Coast of Sussex, April 1850, JV. Stn. 

 Plate XV. 126. 



Genus 18. AMPHIPLEURA, KUt::. 

 Frustules free, linear ; V. with longitudinal ridges. 



The structure of the present genus is somewhat obscure. I have 

 not been able to detect the nature of the ridges so conspicuous on 

 the front view, nor to determine the parts of the valve from which 

 they project. Ehrenberg, in his great work Infusionstliierchen, taf. xiii. 

 fig. iii. 7, gives an ideal section of the frustule, which represents the 

 ridges as springing from the surface of a convex valve, having between 

 them a depression which corresponds in position with the ordinary 

 median hue of the Naviculce. I am unable to confirm this description, 

 although I have on frequent occasions examined the Hving and dry 

 valves. 



1. Amphipleura pellucida, K'dtz. Frustules linear-lanceolate. 

 Length -0033" to -0054". v.v. 



Kiitz. Bacill. iii. 52. Aulacocystis pellucida, Hass. Alg. cii. 8. Nav. jjellu- 

 cida, Ehr. Inf. xiii. 3. Prit. Anim. iii. 140. xvi. 1. 



Fresh water. Lewes, Nov. 1850, W. Sm. Katefield, Lancashire, Jan. 

 1851, Mr. G. Smith. 



Plate XV. 127. 



2. Amphipleura sigmoidea, TV. Sm. Frustules sigmoid. Length 

 •0058" to -0138". v.v. 



Amphipleura rigida, 'Kiitz. Bacill. iv. 30. ad specim. authen. quae communi- 

 cavit cl. De Brcbisson. 



Marine and brackish water : forms a distinct pellicle or stratum. Bexhill, 

 Sussex, Sept. 1850, W. Sm. Lancing, Nov. 19, 1852. 



Plate XV. 128. 



