BRITISH DIATOMACE.E. 25 



5. Eupodiscus sculptus, n. sp. V. striated^the central striae form- 

 ing a quatrefoil ; processes two. Diam. '0013" to '0025". v.s. 



Marine. Poole Bay, Sept. 1851, W. Sm. 

 Plate IV. 42. 



Genus 8. ACTINOCYCLUS, Ehr. 



Frustules free or adherent, disciform; valves cellular, undulated; 

 pseudo-nodule central, conspicuous. 



The undulations on the surface of the valves appear on the side 

 view as radiating bands ; on the front view their true character is 

 easily seen, and they at once distinguish this genus from its allies. 

 It may also be noticed that the cellular structure of the disc is absent 

 from a small portion (pseudo-nodule) in the centre of the valve. 



1. Actinocyclus undulatus, Kiltz. Valve with six rays. Diam. 

 •0009" to -0040". v.v. 



Kiitz. Bacill. i. 24. 



Marine or brackish water : frequent. Poole Bay, Sept. 1849. Near Lewes, 

 Sept. 1850, W. Sm. Near Ipswich, Mr. Hodgson. (Peruvian Guano; Rich- 

 mond, Virginia.) 



Plate V. 43. 



Genus 9. ARACHNOIDISCUS, Bail. 



Frustules adherent, disciform ; valves plane or slightly convex, cel- 

 lular, marked with concentric and radiating lines j pseudo-nodule 

 central, conspicuous. 



This beautiful genus was, I believe, established by Professor Bailey 

 of New York, and has been found in abundance upon Algae collected 

 in Japan, California and South Africa. The discovery of its British 

 habitat is due to M. De Brebisson of Falaise, who detected a single 

 frustule of the species described below on Sphaceluria olivacea, Ag., 

 collected by Mr. Ralfs at Ilfracombe in North Devon. A minute 

 description of this species with carefully executed figures has been 



