Mr. J. Ralfs on the Nostochinex. 325 
the employment of old names, or, renouncing the task as hopeless, 
to invent new ones. In the present group all these difficulties 
have been experienced, and unless authentic specimens, in a fit 
state for examination, exist in the collections of Linnzus and 
other early botanists, it must in some instances be impossible to 
affix their names with any certainty. I cannot flatter myself that 
my nomenclature will be free from error ; but I venture to hope 
that by pointing out the essential peculiarities of these plants, 
and by more detailed descriptions of the species, I shall facilitate 
the labour of those who can find opportunity for inspecting the 
herbaria of original authorities. 
Should I succeed in my endeavours to elucidate the British 
species, the success will be due in a great measure to the kind 
assistance of my fellow-students. Mr. Thwaites, who in Harvey’s 
* Phycologia Britannica’ was the first to recognize three kinds of 
cells, has supplied descriptions of some species which I have not 
met with. Other friends, especially Professor Allman, Mr. An- 
drews, Mr. Jenner, Mr. Moore, the Rev. T. Salwey, and Mr. W. 
Thompson, have aided me by specimens accompanied with re- 
marks ; whilst Mr. Borrer has enabled me, by means of his rich 
botanical library, to clear up poimts on which I must otherwise 
have remained in doubt*. 
* The following synoptical table will, it is hoped, convey a clear idea of 
the characters distinguishing respectively the various genera proposed to be 
described. The genus Nostoc is not included in the present paper on ac- 
count of the necessity which exists of a further exammation and study of 
its several species, some of which have been stated by Professor Kiitzing 
and M. Fries to be merely a condition of species of Codlema. 
Synoptical Table of Genera. 
I. Filaments not included in a membranous sheath. 
a. Frond definite. 
1. Monormia, Berkeley. 
6. Frond indefinite. 
2. Trichormus, Allman. Vesicular cells interstitial and terminal. Spo- 
rangia formed first from the cells at the greatest distance from the 
vesicular cells. 
3. Spherozyga, Ag. Vesicular cells interstitial. Sporangia formed 
first from the cells nearest the vesicular cells. 
4. Cylindrospermum, Kiitzing. Vesicular cells terminal. Sporangia 
as in Spherozyga. 
5. Dolichospermum, n. gen. Vesicular cells interstitial. Sporangia 
without any definite arrangement, and of unequal length. 
II. Filaments included in a membranous sheath. 
6. Aphanizomenon, Morren. Vesicular cells none? Sporangia usually 
single and of unequal length. 
7. Spermosira, Kiitz. Vesicular cells interstitial, single or sometimes 
two together. Sporangia as in Trichormus. 
