DUBLIN NATUEAL HISTORY SOCIETY. 83 



less degree of curvature, more or less rapidity or slowness of tapering, 

 more or less acute or more or less broadly rounded or truncate apices, 

 and, in the striate species, on more or less fineness or coarseness of, or 

 distance between, the stria?. But I believe such distractions to be here 

 equal in value, and quite as reliable, as more striking characters in other 

 genera — different allied species of Closterium possessing such in different 

 and constant degrees of combination ; and I cannot admit, because the 

 distinctions between certain neighbouring species, as compared with each 

 other, may sometimes depend on a ' more or lees' as regards certain com- 

 mon characters, that therefore good and quite distinguishable species do 

 not exist in this genus. Difficult as it may be (to me at least) to define 

 those distinctions, there is at least always a tout ensemhle, a general 

 contour, a certain definite combination of characteristics in the same spe- 

 cies whenever met with, which, when they impress themselves on the 

 eye and memory, render the identification by no means difficult. I have 

 never seen even a solitary instance of conjugation except of like admitted 

 species with like. I therefore imagine, on the whole, it may be quite 

 possible that certain of the Closteria described by Continental writers, 

 which (if erring, at least I apprehend erriag on the right side) I have 

 been disposed to think are identical with previously described forms, 

 may be really quite distinct, could one but see the actual specimens. 

 But be this as it may, however I may fail to convey by my description 

 the valid distinctions which I conceive to exist between the foregoing 

 Closteria and the nearest allies of each, I have no doubt of them myself, 

 from a careful examination of the living specimens; and I am glad to 

 say, that having had the honour to submit specimens to M. de Brebisson, 

 that my own opinion is coincided in by that high authority. 



Genus — Spihot^nia {Br eh.) 

 Spirotcenia truncata (sp. nov.) 



Specific Characters : — Frond cylindrical, but tapering near the trun- 

 cate ends, endochrome a single, rather closely- won nd spiral band, leav- 

 ing a minute clear space at each end, often containing one or more free 

 granules. 



Locality : — Featherbed Mountain, Co. Dublin ; in small pools. 



General Description : — Frond minute, five to eight times longer 

 than broad; cylindrical, but tapering towards the extremities, ends 



admitted), it would fall under Stauroceras (Kiitz), whereas my plant is perfectly distinct 

 as regards the form of the sporangium, besides differing in that of the frond. But in 

 order to more completely satisfy myself, I requested Mr. Ralfs to allow me to see some 

 of his specimens of C. Ealfsii, and I have to thank him for his kind compliance. Having 

 then compared Mr. Ralfs specimens, and the description and beautiful figure in " British 

 Desmidiese" with my plant, I think there cannot be a shadow of doubt but that C. Pritch- 

 ardianum is wholly distinct in every respect from C. Ralfiii, and I feel satisfied the former 

 has not been before described. There must therefore be some mistake in regard to M. de 

 Brebisson's specimens, but which I have not yet had an opportunity to clear up, and 

 under the circumstances I have thought it advisable to append this note. — W. A. 



