458 Mr. J. Ralfs on the British species of Grammonema. 



ent that I am inclined with Agardh to keep them distinct. In 

 Fragilaria the filaments are very fragile^ breaking in pieces at the 

 slightest touch ; the species do not adhere well to paper ; the frus- 

 tules are siliceous and glass-like, and may be subjected to a red 

 heat without any other alteration than the destruction of the 

 colouring matter, and at each end are two more or less evident 

 pellucid puncta. 



In Grajmnonema there is scarcely any silica, in which import- 

 ant character it differs from most of the Diatomacea ; the fila- 

 ments are not fragile and are highly mucous, adhering firmly to 

 paper or glass, and when di'ied appearing like a mere stain ; the 

 application of nitric acid or a red heat destroys their form, and I 

 can perceive no puncta at the ends of the frustules. 



The filaments are elongated, ribbon-like, and composed of nu- 

 merous frustules which are longer than broad. 



1. G. Jurgensii, Ag. Filaments attenuated, yellowish-brown; frus- 

 tules three to eight times longer than broad, slightly separated at 

 the angles. Ag. Consp. Diatom, p. 63. Fragilaria Jurgensii, Ktz. 

 Synop. Diatom, in Linnsea 1833, p. 587. Fragilaria aurea, Carm. 

 in Hook. Br. Fl. vol. ii. p. 403 ! Harv. Br. Alg. p. 198. Conferva 

 striatula, Jurgens, Dec. 19, no. 6 ! (not Conf. striatula, Dec. 11, 

 no. 7.). 



/3. diatomoides. Filaments turning green when dried. Fragilaria 

 diatomoides, Grev. in Hook. Br. Fl. p. 403 ; Harv. Br. Alg. p. 198 ; 

 Wyatt, Alg. Damn. no. 233 ! 

 On marine algae : spring. 



a. Appin, Capt. Carmichael ; Antrim, Mr. D. Moore ; Land's End 

 and Penzance, 



/3. Kilkee, Mr. Harvey ; Torquay, Mrs. Griffiths ; Mount's Bay. 



In a mass both are dark brown, but much paler if separated 

 in the water. In a the colom' is but little altered in drying, but 

 in /3 it becomes green. 



Filaments elongated, giving a feathery appearance to the plant 

 to which they are attached, very mucous, flexible, gradually 

 attenuated ; frustules under the microscope nearly colourless, 

 three to eight times longer than broad, plane, slightly attenuated 

 at both ends, and hence disconnected at their angles, and as the 

 ends are also often somewhat rounded, the margins of the fila- 

 ment have a crenate appearance. 



Mr. Harvey, to whose liberality I am indebted for specimens 

 of many of Capt. CarmichaeFs plants, has given me a portion 

 of a specimen of ' Fragilaria aurea ' gathered by Carmichael him- 

 self, and also Irish specimens both of that plant and of ' Fragi- 

 laiia diatomoides ' of GrcAdlle. These I have attentively examined, 

 as well as specimens gathered at Torquay and Penzance, and I 



