82 DUBLIN NATURAL HISTORY SOCIETY. 



this species to him, he quaintly added, that his only objection was that 

 he thought his name too long, — I do not assent to this ; but, even if it 

 were, I might reply, that his services in the cause of microscopy have 

 indeed been long, and far more than deserving of this inadequate com- 

 pliment. 



Measurements : — Length of frond, -^j to ^L j breadth, j^q to g-jo'; 

 diameter of sporangium, ^^ of an inch. 



Plate II., Fig. 25, frond with endochrome ; Tig. 26, empty frond ; 

 Fig. 27, conjugating fronds with sporangium, — all magnified 200 dia- 

 meters. 



Affinities and Differences : — To me it seems that there are only four 

 species with which there is any likelihood of this Closterium being con- 

 founded, and those are: — Closterium turgidum (Ehr.), C. attenuatum 

 (Ehr.) (opposed as may seem the specific names of those species), C. 

 acerosum (Ehr.), and C. lanceolatum (Kg.). Closterium Pritchardi- 

 anum agrees with C. turgidum, in its gently curved but slighty taper- 

 ing frond, in its lower margin being curved upwards towards the red- 

 dish apices, in its endochrome possessing longitudinal fillets and a single 

 series of large granules, and in its empty frond being finely striate ; 

 but the former differs from the latter in its less stout and less curved 

 frond, in its conical and truncate, not broadly rounded ends, and in the 

 striae seen on the empty frond being far more fine and close. C. Pritch- 

 ardianum agrees with C. attenuatum in the size and general curvature of 

 the frond ; but the former differs from the latter in its conically-tapered 

 truncate ends, not suddenly contracted (more or less like the handle to an 

 oar) into a conical point, and in the striae on the empty frond being far 

 finer. The lower margin being curved upwards near the extremities 

 seems to give this new species some resemblance to C. acerosum (Ehr.) 

 and to C. lanceolatum (Kg.) ; but I believe the somewhat reddish triin- 

 cate apices and longitudinal striae will readily distinguish it from both. 

 It is less slender in proportion to its length than C acerosum, more so 

 than C. lanceolatum, 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 accurately 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 



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

 sary to compare my Closterium Fritchardianum with C. Ralfsii, 1 have been not a little 

 puzzled to find, in a collection of dried Desmidians which I lately had the pleasure to re- 

 ceive from M. de Brcbisson, certain specimens marked " Closterium Balfiii," which 

 upon examination I cannot perceive to be distinguishable from my C. Fritchardianum. I 

 have not mj'self met with living specimens I could by any means refer to C. Ralfsii, relying 

 of course on the description and figures in "The British Dcsmidiese," and from which, 

 beyond any question, my plant differs completely. Indeed, the prolonged beak-like ex- 

 tremities, as described for C Ralfsii, would at once justify an assumption that the spo- 

 rangium would be cruciately lobed, not orbicular — that is (supposing the genus to be 



