74 BRITISH DIATOMACEjE. 



what setaceous and robust ; and the second including those species 

 whose frustules are imperfectly siliceous, and whose fronds are flaccid 

 and delicate in character ; and while I give the size and form of the 

 frond, generally characteristic of each species, I rely mainly for their 

 discrimination upon the shape, size and striation of the individual 

 frustules. 



In the nomenclature of my species, I have mainly followed Harvey's 

 ' Manual of the British Algae/ because the genus is there more fully 

 described than in any other English work, and because I have been 

 enabled by the kindness of Mrs. Griffiths to examine authentic speci- 

 mens of most of the species adopted by Dr. Harvey. To attempt to 

 reduce these species to those of Kiitzing's, without specimens of the 

 latter, and guided alone by the descriptions and figures in the ' Species 

 Algarum ' and ' Bacillarien,' would be to introduce further perplexity 

 into a synonymy already sufficiently confused. 



Sect. I. Frustules firmly siliceous : frond usually setaceous. 



1. Schizonema cruciger, n. sp. Frond filiform; filaments impli- 

 cate below, free above, much divided ; frustules crowded ; valves 

 with a distinct stauros, lanceolate, acute; striae distinct, 40 in 

 •001". Length of frond -l" to 1-2". Length of frustule -0033" to 

 •0051". v.v. 



Marine: on larger Algse. Hove, Sussex, March 1851; Hastings, May 

 1852, &c, W.Sm. Hull, Mr. R.Harrison. Cumbrae, Feb. 1854, Mr. R. 

 Hennedy. 



Plate LVI. 354. Plate LVII. 356. 



2. Schizonema helmintosum, Chauv. Frond filiform, or by cohe- 

 sion irregularly submembranous, much and irregularly divided; 

 ultimate divisions short, abrupt ; frustules in single files or crowded ; 

 valves elliptical ; striae 48 in *00l". Length of frond *5" to 2". 

 Length of frustule -0014" to -0019". v.v. 



Ag. Consp. Crit. p. 20. Grev. B. F. p. 412. Harv. Man. p. 210. ad specim. 

 authen. 



Marine : on rocks. Torbay, Mrs. Griffiths. Aberdeen, Dr. Dickie. Poole 

 Bay, Sept. 1851 ; Coast of Sussex, frequent, TV. Sm. Isle of Arran, Aug. 

 1853; Frith of Clyde, March 1854, Dr. Arnott. Exmouth, Miss Cutler. 



