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



ends of which appear as puncta along the margins of the front 

 view. Ag. Consp. Diatom, p. 40 ; Kutz. Synop. Diatom, in Lin- 

 naea 1833, p. 558. f. 37 ; Harv. Br. Alg. p. 205. Meridion vernale. 

 Eh. Die Infus. p. 207. t. 16. f . 2 ; Pritch. Infus. p. 223. f. 177- 

 179 ; Bailey, Amer. Bacil. in Amer. Jour. Sci. Jan. 1842, pi. 2. 

 f. 42. Echinella circularis, Grev. Crypt. Fl. t. 35. 

 Limerick, Mr. Harvey. Aberdeen, Dr. Dickie ; Stevenston, Ayr- 

 shire, Rev. D. Landshorough. Tunbridge Wells, Mr. Borrer ; Lewes, 

 Mr. Jenner ; King's ClifFe, Rev. M. J. Berkeley ; Oswestry, Rev. T. 

 Salwey ; Cheshunt, Mr. Hassall ; Penzance, St. Ives, Tavistock, Dol- 

 gelley, Caernarvon. 



This forms a fringe on aquatic plants or a mucous stratum on 

 wet rocks. It is hyaline with a brown tinge and becomes green 

 in drying. In a young state, when the frustules are solitary or 

 binate and attached to a loose mucous base, it is liable to be mis- 

 taken for a species of Styllaria; afterwards however, as its frustules 

 repeatedly divide longitudinally without separating, they are ar- 

 ranged in segments of circles. I have never seen more than half 

 a circle formed in this way, which consisted of from twenty-two 

 to twenty-six frustules. Kutzing figures a complete circle with- 

 out a break, but he is evidently wrong ; for if the regular line of 

 frustules was extended until the ends met they would not unite, 

 but overlap or form a spiral, as figured by Ehrenberg*. 



The frustules vary much in length ; they have in front two con- 

 spicuous puncta at the upper end and from five to twelve along 

 each lateral margin, which produces a beaded appearance. These 

 puncta are largest towards the upper end, and gradually become 

 less evident as they are placed lower down, and generally are not 

 visible near the lower end. The endochrome in drying generally 

 retires to the margins, leaving the centre colourless ; it is at first 

 homogeneous, but finally becomes granular. Lateral surfaces nar- 

 row, clavate, with a few distant, strongly marked, transverse striae, 

 which are most evident near the upper end and wanting near the 

 base. 



Plate XVIII. fig. 1. Meridion circulare. 



2, M. constrictum. Lateral surfaces constricted below the apex, 

 transversely striated ; the ends of the striae forming puncta along 

 the margins of the front view. 



This is one of the additions to our flora, for which I am in- 

 debted to Mr. Jenner, whose discoveries have added so largely to 

 the Sussex Cryptogamia, and who is as indefatigable in his re- 

 searches as he is accurate in his observations. Mr. Jenner finds 

 it rather plentifully in the Cold Bath Spring, Tunbridge Wells, 



• Since the above was written I have gathered specimens at Dolgelley 

 which formed a spiral as figured by Ehrenberg. 



