2o2 ARCHER^ ON A NEW SPECIES OF COSMARIUM. 



contracted (more or less like the handle to an oar) into 

 a conical pointy and in the stripe on the empty frond beinj; 

 far finer. The lower margin being curved upwards near the 

 extremities, seems to give this new species some resemblance 

 to C. acerosum, War., and to C lanceolutum, Kg. ; but I 

 believe the somewhat reddish, truncate apices and longitu- 

 dinal striae will readily distinguish it from both. It is less 

 slender in proportion to its length than C. acerosum, more so 

 than C. lanceolatu7n, .and the upturned conico -truncate ends 

 seem to me very characteristic. There appears to me no 

 danger of mistaking this form for C. Ralfsii, so decidedly 

 distinguished by its turgid, ventricose body, and prolonged, 

 beak-like extremities."^ 



Closterium is a genus in which it is difficult always accu- 

 rately to define in words the specific distinctions, resting in 

 allied species, as they frequently do, on more or less stoutness 

 or slenderness of frond, more or 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 coarse- 

 ness of, or distance between, the striae. But I believe such 

 distinctions 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 con- 

 stant degrees of combination ; and I cannot admit, because 



* Notwithstanding that, when reading this paper, I had almost thought it 

 unnecessary to compare my Closterium Pritchardianum witli C, Ralfsii, I 

 have been not a little puzzled to find, in a collection of dried Desmidiaus 

 which I lately had the pleasure to receive from M. de Brebisson, certain 

 specimens marked " Closterium Ralfsii,''' which, upon examination, I cannot 

 perceive to be distinguishable from my C. Pritchardianum. I have not myself 

 met with living specimens I could by any means refer to C. Ralfsii, relying, 

 of course, on the description and figures in ' The British Uesmidese,' and 

 from which, beyond any question, my plant differs completely. Indeed, the 

 prolonged, beak-like extremities, as described for C. Ralfsii, would at once 

 justify an assumption that the sporangium would be cruciately lobed, not 

 orbicular, that is (supposing the genus to be 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. Ealfs to allow me to see 

 some of his specimens of C. Ralfsii, and I have to thank him for his kind 

 compliance. Having, then, compared Mr. B.alfs' specimens, and the descrip- 

 tion and beautiful figure in 'British Desmidiese' with my plant, I think 

 there cannot be a shadow of doubt but that C. Pritchardianum is wholly dis- 

 tinct in every respect from C. Ralfsii, 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. 



