BRITISH DIATOMACEiE. 2/ 



moniliform, 27 in -001". Length of frustule -0019" to -0072". 

 Stipes usually clustered, from *0006" to •0192" in length, v.v. 



ft. V. oval or broadly elliptical, v.v. 



y. Frustule deeply geniculate, v.s. 



Ag. Syst. p. 1. Ag. Consp.p. 58. Eng. Bot. 2nd ed. pi. 2560. Grev. B. F. 

 p. 404. Harv. Man. p. 200. Ehr. Inf. xx. 1. Ralls, Ann. vol. 13. 

 pi. xiv. 7. ad specim. authen. in Herb. Jenn. Kiitz. Bacill. xx. 1. 

 Quek. H. C. xii. 8. Conferva stipitata, Eng. Bot. 1st ed. pi. 2488. 

 Achnanthes Carmichaelii, Grev. B. F. p. 404. Harv. Man. p. 200. Kiitz. 

 Bacill. xx. 2. Achnanthes brevipes, Kiitz. Bacill. xx. 9. 



Marine. Parasitic on other Algae. Poole Bay, June, and in conjugation, 

 July 1849. Jersey, July 1852. Larne, Ireland, July 1853. Newhaven, 

 Sussex, Oct. 1853, W.Sm. Southampton, April 1844, Mr. Jenner. South- 

 ampton, July 1812, Miss Hill and Miss Biddulph ; communicated by Mrs. 

 Griffiths. Var. ft. Seaford, Sussex, April and Sept. 1851, and in conjugation, 

 March 1852, W. Sm. Var. y. Newhaven, Sussex, July 1843, Mr. Jenner. 

 (Mediterranean near Marseilles. Salt Pits near Agde, May 1854, W. Sm.) 



I have included under the above both A. Carmichaelii, Grev., and A. brevi- 

 pes, Kiitz., neither species, judging from the figures in the ' Bacillarien,' having 

 any distinctive characters save the greater or less length of the stipes ; while 

 in all my various specimens this feature is of the most variable kind, frustules 

 nearly sessile, and others with a stipes ten times their own length occurring in 

 the same cluster. "With regard to Var. ft. I am in doubt whether it should 

 not be ranked as distinct, the broadly elliptical form of the frustule being 

 tolerably constant, and the habit of growth more diffuse and scattered than in 

 my other specimens. It has also maintained its characters unchanged for 

 several successive seasons, disappearing and being again produced in the same 

 pool without any apparent change in its form or habit ; at the same time, 

 forms intermediate between it and the most linear and clustered specimens of 

 A. longipes have so often presented themselves in the same and other localities, 

 that I do not feel myself warranted in elevating the Seaford plant into a 

 distinct species. 



The presence of costse is alone sufficient to distinguish A. longipes and its 

 varieties from the other species of this genus. These costse appear to be 

 thickenings on the under surface of the siliceous valve, and not, as in others 

 of the Biatomacece, confluent beaded striae ; the latter extending, as is ordi- 

 narily the case, 'over the entire surface of the valve, though the regularity of 

 their arrangement is much obscured in the present species by the interference 

 produced by the underlying costse. 



Plate XXXV. 300. Plate XXXVI. 300. Var. ft. Plate XXXVI. 300 ft. 

 Var. y. Plate XXXVI. 300 y. 



2. Achnanthes brevipes, Ag. Filaments containing from 2 to 

 several hundred frustules ; V. linear or oval, attenuated or acute, 



