86 BRITISH DIATOMACE^E. 



13. Eupodiscus Ralfsii, W. Sm. Cellules in radiate series, forming 

 distinct zones; process (?) single, submarginal; valve iridescent; 

 cellules 18 in -001". Diameter -0018" to -0042". v.v. 



Marine. Ilfracombe, June 1853, Mr. Ralfs. Cumbrae, Frith of Clyde, 

 Feb. 1854, Mr. Hennedy. (Cherbourg, 31. De Brebisson.) 



This species, together with E. fulvus and E. crassus of the present work, 

 probably belong to the genus Actinocyclus, Ehr. ; but as I have limited that 

 genus to frustules with undulated valves, I am obliged to place these apart. 

 Their position in Eupodiscus is, however, doubtful, as the process in all is 

 rather a pseudo-nodule than a projection from the surface of the valve. 



The lines of cellules in the present species diminish in number at distinct 

 intervals from the margin towards the centre of the valve, giving a zoned ap- 

 pearance to its surface when seen under a low power, the lines that reach the 

 centre dividing the area of the valve into apparent rays of cellules. 



The colour under a low power is a rich iridescent purple of various hues. 



I have carefully examined various Guanos containing discs of Ehrenberg's 

 multitudinous species of Actinocyclus, but cannot satisfy myself that the pre- 

 sent is precisely identical with any figured in the ' Microgeologie ' : in no case 

 does Ehrenberg notice the pseudo-nodule, which he could hardly have over- 

 looked. 



14. Actinocyclus duodenarius, W. Sm. Valve with twelve rays. 

 Diameter -0037", &c. v.s. 



Actinoptycus duodenarius, Ehr. in Kxitz. Sp. Alg. p. 131 ; Microg. xviii. 24. 

 Marine. Medway, March 1854, Mr. Dallas. 



15. Actinocyclus sedenarius, Roper. Valve with sixteen rays. 

 Diameter -0048", &c. v.s. 



Roper, Mic. Trans, vol. 2. pi. vi. 2. Actinoptycus sedenarius, Ehr. in Kutz. 

 Sp. Alg. p. 131 ; Microg. xviii. 26. Kutz. Bacill. i. 23. 



Marine. Medway, Mr. Dallas. Thames, Mr. Roper. Near Caermarthen, 

 Aug. 1854, Mr. Okeden. 



1 6. Actinocyclus octodenarius, W. Sm. Valve with eighteen rays. 

 Diameter *0054", &c. v.s. 



Actinoptycus octodenarius, Ehr. in Kxitz. Sp. Alg. p. 131. 



Marine. Medway, Mr. Dallas. 



The last three forms are probably the same species in different stages of 

 growth. I have placed them all in Actinocyclus, for in all the surface of the 



