42 BRITISH DIATOMACEiE. 



Genus 43. GRAMMATOPHORA, Ehr. 



Frustules oblong, adhering by their opposite and alternate, or more 

 rarely by their adjacent angles into a zigzag chain, annulate and 

 septate, definite ; septa opposite, usually more or less curved ; 

 valves linear or elliptical. 



The curvatures of the septa, which are very conspicuous in most 

 species, appear like lines of written characters on the F. V. of the 

 frustule, and justify the very significant name given to the present 

 genus. 



In some species these flexures are, however, very slightly marked ; 

 in others entirely absent ; so that the distinctive character of the 

 genus must be sought for in its zigzag filament, definite frustule, and 

 opposite septa. One or other of these features distinguish it from 

 Rhabdonema, Striatella, and Tetracyclus on the one hand, and Tabel- 

 laria on the other ; while the annulate character of the frustule sepa- 

 rates it from any other form. Thirteen species of Grammatophora 

 are described in the ( Species Algarum ' ; but many of these differ 

 only in their relative size and the outline of the valve. Looking at 

 the great diversity that may be found in G. marina and G. serpentina 

 in these respects, I am disposed to believe that most of the above 

 forms may be reduced to these very common species, 



1. Grammatophora marina, R'titz. Septa with a single curvature 

 near the margin of the frustule; valve elliptical or linear-lanceo- 

 late, occasionally linear, with slightly attenuate and capitate extre- 

 mities, striated ; striae 44 in -001". Length of frustule "0005" to 

 •0051". Breadth of valve -0002" to -0005". v.v. 



Kiitz. Bacill. xvii. 24 ; Sp. Alg. p. 120. Diatoma marinum, Lyng. Tent, 

 lxii. A. Ag. Consp. p. 53. Ralfs, Ann. vol. 11. pi. ix. 5. Grev. B. F. 

 p. 405. Harv. Man. p. 201. Conferva tceniceformis, Eng.Bot. tab. 1883. 

 Ag. Consp. p. 54. Diatoma brachygonum, Grev. B. F. p. 406. Harv. 

 Man. p. 202. 



Marine: very frequent. Torbay, July 1846 ; Poole Bay, July 1 848 ; Coast 

 of Sussex, Aug. 1850 ; Cork Harbour, June 1855, &c., W. Sin. (Mediterra- 

 nean Sea near Marseilles, May 1854, W. Sm. Mauritius, Dr. Arnott.) 



Plate XLII. 314. 



