BRITISH DIATOMACEiE. 85 



valve regularly convex ; margin of basal segment slightly concave ; 

 strife 24 in -001". Length -0013". Breadth of valve '00025". v.s. 



W. Sm. in Grev. Ann. 2nd ser. vol. 15. pi. ix. 5. 

 Freshwater. Braemar, Aug. 1854, Dr. Balfour. 



9. Cymbella Arcus, Greg. Dorsal segment of valve much larger 

 than basal, convex, with a slight central elevation ; margin of basal 

 segment plane ; nodule submarginal, extremities produced, capi- 

 tate ; striae 40 in -001". Length -0014". Breadth of V. -0002". 

 v.s. 



Greg. Mic. Journ. vol. iv. pi. 1. 21. 



Fresh water. Near Hamilton, Br. Gregory ; communicated by Br. Arnott. 



10. Amphora affinis, W. Sm. 



Var. /3. Extremities produced, v.s. 



Amphora Arcus, Greg. Mic. Journ. vol. 3. pi. iv. 4. v.s. 



Brackish water. Lough of Skaill, Orkney, Aug. 1855, Rev. J. Pollexfen ; 

 communicated by Br. Greville. 



11. Coscinodiscus concinnus, n. sp. Cellules arranged in radi- 

 ating lines, equal except in centre of valve, where there occur three 

 to eight larger cellules ; cellules 24 in •001". Diameter -0025" to 

 •0056". v.v. 



Marine. Stomach of Pecten, Coast of Sussex, Feb. 1854, and Kinsale Bay, 

 April 1855, W. Sm. Frith of Clyde, Nov. 1854, Mr. Hennedy. Cumbrae, 

 Feb. 1855, Br. Arnott. 



This may be C. centralis, Ehr. in Kiitz. Sp. Alg. p. 123; but the figure 

 of that species in Microg. xviii. 39 has a distinct marginal ring, which is 

 wanting in my specimens ; moreover, the cellules in C. coneinnus are too 

 minute to have been detected by the instrument used by Ehrenberg. 



12. Coscinodiscus perforatus, Ehr. Cellules in radiating lines, 

 equal, centre smooth; 9 cellules in *001". Diameter up to - 01" 

 {Roper, in lit.), v.s. 



Marine. Thames mud, Aug. 1854, Mr. Roper. Medway, March 1854, 

 Mr. B alias. 



I need hardly say that there is no perforation in the centre of the valve, as 

 the name would imply. 



