it has been detected elsewhere. The Alga on which it grows is 

 so very widely scattered that our ElacMstea ought, probably, to 

 have a place in many distant floras, but its minute size has 

 hitherto been its protection. It looks so much like the fructi- 

 fication of the Dictyota, when carelessly examined with the 

 naked eye, or with a lens of small power, that it may often be 

 passed over as such ; and I was once disposed to think that it 

 might be merely a diseased proliferous state of that fructification. 

 This opinion I have long abandoned, and recognised this produc- 

 tion as a parasite, and true member of the genus ElacMstea. 

 In this latter point, however, I am at issue with my friend 

 Professor J. Agardh, who places E. stellulata in the genus Myrio- 

 nema. As far as size and outward characters go, such a position 

 seems natural, but it will be found on closer inspection, that the 

 filaments here are of two kinds, exactly as in ElacMstea, and that 

 they spring not from decumbent, adnate filaments, as in Myrio- 

 nema, but from erect, radiating ones, compacted into a little 

 tubercle. 



Fig. 1. Part of a frond of Dictyota dichotoma, infested with the Elachistea : — 

 of the natural size. 2. Some of the tufts on a portion of the membrane : — 

 magnified. 3 . Vertical section of a part of tuft, most of the filaments 

 removed : — highly magnified. 



