CORRESPONDENCE. 85 



once recognized by anyone conversant with the two forms. Dr. 

 Edwards seems to base his opinion on his examination of Moller's 

 Typen Platte and Dr. Woodward's figiu"es ; of the latter I can say 

 nothing as I have not seen them, but as to the former I would observe 

 that in my Moller's Typen Platte, the specimen of this diatom is a 

 three and not a four sided form, and corresponds exactly with Dr. 

 Wallich's figure and description, and is identical with my other speci- 

 mens of Trie, fimhriatum. MoUer is undoubtedly in error in assigning 

 the species to Brightwell instead of to Wallich, but this does not 

 affect the question whether or not it is a distinct species, and what- 

 ever Moller's inaccuracies in his index I feel sui*e everyone must 

 admit the marvellous skill which has produced such a specimen 

 of mounting as his Typen Platte. Trie, fimhriatum can, I contend, 

 be easily known by the convexity of its sides. Of Trie, favus, the 

 original type of the genus, I have examined hundreds of specimens, 

 but never found one of similar outline to Trie, fimhriatum. The sides 

 of Trie, favus are " planis aut leviter convexis " ( ' Kutz. Bacill.,' p. 139), 

 or as Ealfs has it, " straight or slightly convex " (' Prit. Inf.,' 1. c). 

 Those of Trie, fimhriatum are, however, convex, forming, as Dr. Wal- 

 lich, while noting the constant character of the outline as a remark- 

 able feature (' Micr. Journ.,' vi., p. 248), goes on to describe, the arcs 

 of circles, the radius of which is the distance to the opposite angle. 

 Though neither have I seen Dr. Wallich's original specimens of Trie, 

 fimhriatum, I have in my cabinet valves of it from Saint Helena, the 

 habitat mentioned by him, which entirely bear out the above, and 

 would alone, I think, cause Dr. Edwards to modify his opinion. I 

 would observe that Dr. Wallich's figixre (' Micr. Journ.,' vol. vi., 

 PI. 12, /. 5) is a little inaccurate in showing the rows of hexagonal 

 cellules as straight, instead of following the same curve as the sides, 

 a feature which adds much to the beauty of the form. 



A similarity in outline to Trie, fimhriatum as to the convexity of 

 the sides which exists in the figure of Trie, grande (Brightw,, ' Micr. 

 Journ.,' vol. i., PI. 4,/. 8), which apparently ('Micr. Journ.,' vol. iv., 

 p. 276) is the same as Trie, orientale of Harv. and Bail., leads me to 

 notice the double description by Dr. Greville of Trie. Boherlsianmn. 

 In ' Micr. Journ.,' vol. xi., PI. 9, /. 9, he describes and figm-es a 

 diatom from Sydney under this name, and, apparently forgetful of this 

 description, again in ' Micr. Trans.,' vol. xiv., p. 7, PI. 2, /. 22, 

 where he queries it as identical with Trie, grande. Though Dr. Gre- 

 ville's two descriptions and figures of Trie. Bohertsianum differ some- 

 what, yet they relate, I conclude, to the same form. 



Whether they and Trie, grande, Trie, orientale, and Trie, fimhriatum 

 should all be united in one species, I have no means of judging, beyond 

 comparing the descriptions, figures, and habitats above referred to ; but 

 I think it quite probable an examination of the original specimens 

 might lead to that conclusion. However that might be, I do not see 

 my way at present to ranking Trie, fimhriatum under Trie, favus. 



Yours obediently, 



H. Eamsden. 



