VI PREFACE. 



Falaise by M. de Brebisson, but most of them have also 

 American habitats. 



It has been mj' desire throughout to write impartially, and 

 I am not aware that I have, in a single instance, neglected 

 the claim of priority, or appropriated to myself the disco- 

 veries of others. Should any blemishes of this kind appear, 

 they will, I trust, be attributed to the circumstance that this 

 work has been composed at a distance from the metropolis, 

 and without access to many works which it would have been 

 desirable to consult. Amongst these I have more especially 

 to regret that I have not seen some valuable papers on the 

 Desmidiese by Ehrenberg, Corda, and Morren, which have 

 been published in various foreign periodicals. 



In these pages the name appended to a species merely in- 

 dicates the author of the specific name, and has no reference 

 to its genus. This departure from the usual custom seems 

 to me to require no vindication ; for it is surely unjust that 

 the credit due to the discoverer or first describer of a plant 

 should be ascribed to one whose sole merit in regard to it 

 has been to transfer it from one genus to another. To those 

 who prefer the common method, the synonyms will afford 

 the requisite information. 



I consider Merismopedia and Trochiscia to belong to the 

 Palmelleae, and have therefore omitted them, although Kiit- 

 zing and Meneghini include them in this family. I am also 

 unacquainted with any species of Sphcerastrum which can 

 rank with the Desmidiese. 



Penium Digitus, and, except in a few cases which are pointed 

 out, the species of Closterium, Docidium and Micrasterias, are, 

 on account of their comparatively large size, magnified only 

 200 diameters, but all the others are magnified 400 diameters. 



