MERIDION. 419 



2. MEKIDION CONSTRICTUM Rolfs. 

 Plate XCVI. Figs. 7, 8, 9. 



Char. Articulating surfaces constricted at the broader end, 



striated ; the striae forming puncta in the front view. 

 Meridion constrictum Ralfs, in Annals, voL xiii. p. 458. 

 pi. xiii. fig. 2. ; Jenner, in Flora of Tunbridge Wells, 

 p. 206. 



" This is one of the additions to our Flora, for which I 

 am indebted to Mr. Jenner, whose discoveries have added so 

 largely to the Sussex Cryptogamia, and who is as indefatigable 

 in his researches as he is accurate in his observations. Mr. 

 Jenner finds it rather plentifully in the Cold Bath Spring, 

 Tunbridge Wells, growing on Fragilaria virescens. I have 

 received from him both dried and recent specimens. In the 

 latter I find the frustules solitary or binate, the circles being 

 entirely broken up before the specimens reached me ; but 

 Mr. Jenner informs me, that when gathered, they are united 

 together so as nearly to form a circle. As, however, they 

 are not arranged on a plane as in Meridion circulare, but 

 stand nearly erect, somewhat like the staves of a tub which 

 is broader above than below, when they are dry and fall 

 down they necessarily separate, and gaps are produced in the 

 circular outline. In the dried specimens I find some of the 

 frustules arranged in a circle, which, however, exhibits the 

 gaps already noticed, whilst others seem to be fasciculated. 



" The front view cannot be distinguished from a frustule 

 of Meridion circulare, with which it agrees in size and form, 

 and also in having two conspicuous terminal puncta, and a 

 series along the lateral margins. As in Meridion circulare, 

 the lateral surfaces have a few distinct, strongly marked 

 transverse striae ; but they differ from it most remarkably in 

 the constriction below the apex." Rolfs. 



In the very deep frustules the constriction is almost lost. 



EE 2 



