ARCHER^ ON closti;riua[ aciculare. 33 



distinctiou that could be relied on as of specific impovtauce. 

 In this Closterium, as in a few other species, conjugation 

 takes place immediately after the act of self-division, so that 

 one (the younger) segment is considerably shorter than the 

 other (the older) ; and here in the act of conjugation each of 

 the longer (and of course also each of the shorter) segments 

 are pointed in opposite; directions, the empty segments re- 

 maining for some time attached to the orbicular sporangium, 

 Avhich is surrounded by a conspicuous hyaline mucous invest- 

 ment. In all these respects my specimens agreed with M. de 

 Brebisson's ; and I take the opportunity to draw attention to 

 them here, because I conceive it to be a probability that sucli 

 circumstances attendant on conjugation, as those I above 

 point out, may be eventually found to have perhaps a spe- 

 cific importance, and to be in certain cases specially charac- 

 teristic. 



If I be right, then, in anticipating for C. aciculai'e a lobed 

 sporangium, besides the characteristic difierence in the 

 general external outline, such a further difference, more 

 recondite it is true, but most probably of greater (certainly I 

 should saj- of considerable) importance would, so far as I can 

 see, place them apart. 



It will have been gathered from the foregoing, that it is 

 amongst those species falling under the genus Stanroceras 

 (Kiitz.), that I imagine the nearest allies of C. aclculare are 

 to be found ; but it is precisely the uncertainty in regard to 

 the actual mode of conjugation, and of the sporangial con- 

 dition in a few species, and which of course direct observa- 

 tion alone can remove, that renders the value of that genus 

 doubtful. It may hereafter be found to be a good and 

 natural genus, but C. luceatum, (Ehr.) and C. TLhrenhergii 

 (Menegh.) present remarkable peculiarity also in their conju- 

 gation ; and it seems more advisable, then, to look on those 

 species which would rank themselves under Stanroceras 

 (Kiitz.), for the present at least, as merely a subdivision of 

 Closterium (Nitzsch) . 



Of British Closteria, undoubtedly belonging to that group 

 the most slender is C. setaceum (Ehr.) ; but that species is 

 wholly and unmistakeably distinct from C. aciculare, by its 

 narrow-lanceolate, rather inflated body, and striate frond, 

 as well as by its length being not so great. As to Conti- 

 nental species of an intermediate character, C. elegans (Breb.) 

 is also quite distinct on account of its narrow-lanceolate 

 body, its under margin being somewhat ventricose, nor are 

 the colourless setaceous extremities so much prolonged. It is, 

 however, C. pj'onum (Breb.) that presents any serious diffi- 



VOL. II. NEW SER. C 



