400 DIATOMACE2E. 



Hab. Everywhere common in ditches and rivulets. 



" In a stream below Penmaen Pool, near Dolgelly ; and 

 within the influence of the tides, I have gathered a tufted 

 state of this species of a bluish colour, not unlike the iridescent 

 tints of Cystoseira ericoides. It was growing with Ectocarpus 

 littoralis. I have also for several years observed it in the 

 same state in a cave by the sea side at Penzance ; in both 

 instances it afterwards became brownish, and finally green." 

 Ralfs. 



It is on this species that the inflated vesicles usually occur, 

 and which formerly induced me to refer it to a section of the 

 genus Vesiculifera, 



4. MELOSEIRA OCHRACEA Ralfs. 



Char. " Frustules very slender, convex at each end, ovate, not 

 striated, ferruginous. Filaments often connected together 

 in a subramose manner." 



Gallionella ferruginea Ehr., Die Infus. p. 169. t. 10. fig. 8., 

 and t. 21. fig. 3. Conf. ochracea Dillw., t. 62. Oscil- 

 latoria ochracea Grev., Flor. Edin. p. 304. ; Harv. Br. 

 Alg. p. 167. M. ochracea Kalfs, in Annals, vol. xii. 

 p. 35. 



Hab. Pools and slow streams in boggy soils. 



" This plant occurs in delicate ochraceous or ferruginous 

 masses, falling into powder on the slightest touch. The fila- 

 ments are so slender, and the joints so obscure, that I have 

 been unable to determine the form of the frustules, and have 

 therefore taken the specific character from Ehrenberg : I am 

 also unable to ascertain whether the joints are marked by any 

 central line. Having received from Mr. Dillwyn a specimen 

 of his Conf. ochracea, which I am able confidently to refer to 

 this species, I have restored the original specific name. 

 Ehrenberg is no doubt correct in placing the plant in this 

 genus, as the filaments are cylindrical and silicious. 



" When submitted to a red heat it acquires a reddish tinge, 



