Mr. J. Ralls on the Diatomacew. 351 



Not imfrequently this species has the joints here and there di- 

 lated into a globular form as described by Kutzing ; in this state 

 it much resembles a species of Vesiculifei^a, Hassall ; and indeed 

 Mr. Hassall, whose researches have so much extended om- know- 

 ledge of the freshwater Alg?e, was induced by this resemblance 

 to refer it to a subdinsion of that genus, in one of his valuable 

 and interesting papers on the British freshwater Confervre ; but 

 since his paper was published he has agreed with me in opinion 

 that his V. composita is undoubtedly the Mehseira varians of 

 Agardh, and not a species of Vesiculifera. "N^lien the joints are 

 thus dilated, the central furrow gives the appearance of two 

 joints combining in the formation of the inflated cells. 



Plate IX. fig. 5. Mehseira varians. 



6. M. orichalcea, Kutz. Filaments slender ; frustules two to three 

 times longer than broad, marked with two central lines ; junction- 

 surfaces striated, closely united. Kutz. in Linnaea 1833, p. 71. 

 fig. 68. fialUonella aurichnlcea, Eh. Die Infus. p. 168. t. 10. fig. 6; 

 Pritch. Infus. p. 200; Bailey, Amer. Bacil. part 2. p. 5. pi. 2. 

 fig. 4 b. 



In freshwater ditches and slow streams. Cheshunt, Mr. Hassall; 

 Stevenston, Ayrshire, Rev. D. Landshorough ; DolgeUey. 



Bro^ATiish when recent ; it becomes paler in di-jdng. 



Tlie filaments are liner than in M. varians ; joints Iavo to three 

 times longer than broad, with two lines near the centre ; ends 

 closely united in the same manner as in 31. arenaria, but the den- 

 tated appearance of the ends of the stri?e is less evident ; junc- 

 tion-sm'faces flat with radiated stria?, which are often veiy obsciu'c 

 in the centre, but generally plainly developed round the margin. 



This species is likely to be mistaken for M. varians; but its 

 filaments are more slender and more uniform in size, the joints 

 are longer, more closely united, and especially it difi'ers in ha^'ing 

 two central lines and striated junction-sm-faces, and in not tm'n- 

 ing green in drjdng. 



Kutzing figm*es this species vn.t\\ joints occasionally enlarged 

 in the same manner as in M. varians. 



Mr. Hassall first detected it in this country. 



Plate IX. fig. 6. Meloseira orichalcea. 



*** Filaments very slender ; joints obscure. 



7 . M. ochracea. Frustules very slender, convex at each end, ovate, 

 not striated, ferruginous ; filaments often connected together in a 

 subramose manner. Gallionella ferruginea. Eh. Die Infus. p. 169. 

 t.. 10. fig. 8. and t. 21. fig. 3 ; Pritch. Infus. p. 200. figs. 129, 130. 

 Conferva ochracea, Dill. t. 62 ! Oscillatoria ochracea, Grev. Fl. 

 Edin. p. 304; Harv. Br. Alg. p. 167. 



Pools and slow running streams, especially in boggy soils. 



