ZOOLOGICAL AND BOTANICAL ASSOCIATION. 1 1 1 



the form of the joints in each species. In Spharozosma vertebratum it is 

 more apparent, because the constricted form of the joints renders it in- 

 evitable that the growing segments should be at first smaller and nar- 

 rower than the older ones ; in the form under consideration, however, 

 the nascent segment has only to grow longitudinally to form a continuous 

 cylinder with the opposite older segment. Having thus (at least to my 

 own satisfaction), even without this last conclusive evidence, proved 

 the form, of which I hope I have succeeded in conveying a satisfactory 

 conception, to be a true Desmidian, of which group there can be no 

 doubt it is a new species, I will now assume both these points conceded, 

 when the next question becomes — to what genus of DesmidiacesB does 

 this plant belong ? Confining our attention for a moment to a single 

 joint, it might seem to possess as good a right to a place in the genus 

 Docidium as Docidium asperum (Br 4b.), as described in Ralfs, but I shall 

 presently give, I believe, valid reasons, why I think neither of these or- 

 ganisms would be rightly placed in Docidium, and, if not in that genus, 

 certainly not in any other known. 



On a former occasion, when I had the honour to lay before the As- 

 sociation the first part of a Catalogue of Dublin Desmidiaceae, I appended 

 to the mention of Docidium asperum {Br 4b.) a note of my having met 

 that species forming short filaments. Now, I have since, on several 

 occasions during last summer, met with it, and always forming fila- 

 ments of indefinite length, but being usually mixed with other Algae, 

 never in very large quantity; frequently, however, detached cells occur, 

 more especially when kept some time in the house. In addition to the 

 fact of this species forming filaments, which is not alluded to in Ralfs, I 

 have met specimens possessing, when fresh, in nearly every joint, a pale 

 central space or division of the endochrome into two equal portions, and 

 contracted in an irregular manner enclosing a single central series of cor- 

 puscles, somewhat like the side or edge view of the endochrome of the 

 form to which I first directed attention, and sometimes disposed in a 

 zigzag or subspiral manner, while possessing all the other characteristics, 

 as described in Ralfs : I allude to the roughness, owing to minute scat- 

 tered granules, and to the dilated extremities (Fig. 5). There can be no 

 doubt whatever that it is the same plant. When a joint is fractured, it 

 breaks at the middle, but not with so smooth a line of fracture as the before 

 described form. There has also occurred to me another form nearly allied 

 to Docidium atperum, but I believe a distinct species, being altogether a 



