350 Mr. J. Ralfs on the Diatomacese. 



In drawing up the above description I have availed myself of 

 Mr. Moore^s notes. 



Ehrenberg appears to have confounded this very beautiful and 

 distinct species with Meloseira varians, which I am the more sur- 

 prised at, because he has given very good figures of both plants. 



The characters by which this species is distinguished from 

 Meloseira varians have been so clearly pointed out by Mr. Dal- 

 rymple, that I shall use an extract from his letter instead of 

 making any observations of my own. 



'' Meloseira varians, Ag._, is as clearly Gallionella varians of Eh- 

 renberg, 1. 10. fig. 4, as Meloseira arenaria, Moore, is Gall, variant 

 oft. 21. fig. 2. Still no tyro in natural history could presume 

 that the two were the same species. The characteristic difference 

 exists in the well-marked feature of the strise at the junction-lines 

 of the corpuscles, and which, combined with their discoid form, 

 bears a strong resemblance to the milled heads of many of the ad- 

 justing screws of om' microscope. Added to this is the appear- 

 ance of radiating lines seen when the flat sm'face of the disc is 

 viewed.^' 



Plate IX. fig. 4. Meloseira arenaria. 



5. M. varians, Ag. Frustules once and a half to twice as long 



as broad, with a single central line, the ends slightly rounded ; 



junction-surfaces without striae. Ag. Consp. Diatom, p. 64 ! ; 



Kutz. in Linn^a 1833, p. 71. fig. 69; Harv. Br. Alg. p. 195! 



M. lineata, A^. Syst. p. 8 ; Harv. Br. Alg. p. 195 ! Gallionella 



varians, Eh. Die Infus. t. 10. fig. 4. G. aurichalcea, Bailey, Amer. 



Bacil. part 2. pi. 2. fig. 4 c. Conf. lineata, Dill. p. 44. t. B ; Jurg. 



Dec. 5. no. 10 ! Conf. hyemalis, Jurg. Dec. 17. no. 6 ! Vesiculifera 



composita, Hassall in Annals of Nat. Hist. vol. x. p. 394 ! 



In freshwater rivulets and ditches. King's Cliff", Northampton- 

 shire, Rev. M. J. Berkeley ; frequent in Sussex, Mr. Borrer ; Lewes, 

 Mr. Jenner ; Cheshunt, Mr. Hassall ; Shrewsbury, Mr. Leighton ; 

 Oswestry, Rev. T. Salwey. — Aberdeen, Dr. Dickie -, Stevenston, Ayr- 

 shire, Rev. D. Landshorough. — Antrim and Limerick, Mr. W. H. Har- 

 vey ; Ballycastle and near Belfast, Mr. D. Moore. Tavistock, Ilfra- 

 combe, Penzance, Dolgelley, Caernarvon. 



It is brownish when recent and becomes green in drying *. 



Filaments very slender, but varying much in thickness, fragile ; 

 joints from once and a half to twice as long as broad, with a single 

 central stria, the ends rounded so that the joints are not so 

 closely united as in M. arenaria and M. orichalcea. 



• In a stream below Penmaen Pool near Dolgelley, and within the influ- 

 ence 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 grow- 

 ing 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. 



